HIV-1 Protease Inhibitors

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HIV-1 Protease Inhibitors

Joseph J. Eron, Jr. From the Infectious Diseases Division,University of North Carolina at Chapel Hill

Treatment of human immunodeficiency virus type 1 (HIV-1) infection with regimens thatinclude protease inhibitors (PIs) has contributed to marked improvements in HIV-relateddisease progression and mortality. Five PIs are approved by the US Food and Drug Admin-istration and have potent activity in vitro. PIs with 2 nucleoside analogue reverse transcriptaseinhibitors have demonstrated prolonged suppression of HIV-1 replication in treated patientsand improvements in disease progression and mortality. PIs combined with nonnucleosidereverse transcriptase inhibitors or other PIs produce marked antiretroviral effects. Althoughnot all patients have prolonged responses to PIs, and salvage treatment has had mixed resultsfor patients who have not responded to initial PI therapy or whose HIV RNA levels haverelapsed during such therapy, newer PIs currently being developed hold promise. Most patientscan successfully tolerate PI-including regimens; however, long-term side effects, such as bodyfat redistribution, insulin resistance, and increased serum lipids, are now being observed insome patients receiving PI-including therapy.

The treatment of HIV-1–infected patients has changed dra-matically over the past 5 years. Multiple observations in a va-riety of settings have demonstrated a decrease in mortality dueto HIV-related illnesses, and the incidence of HIV-1–relatedopportunistic infections has decreased [1]. Much of the im-provement in HIV-1–related clinical outcomes has been attrib-uted to the use of protease inhibitors (PIs) in combination an-tiretroviral therapy [2].

In HIV-1, as in all retroviruses, the production of infectiousvirus invariably requires an active viral protease. The protease isa viral-encoded enzyme that consists of a 99-amino-acid proteinthat forms a homodimer. In the replication cycle of HIV-1, aprecursor protein or polyprotein is synthesized. This polyproteinis composed of structural proteins (Gag proteins) and viral-en-coded enzymes, including the reverse transcriptase, integrase, andthe protease itself (reviewed in [3]). Cleavage of the Gag poly-protein is required for the formation of infectious particles. Cellscontaining HIV-1 proviral DNA that does not produce a func-tional protease do produce viral particles, but these particles areimmature and are noninfectious [4].

Knowledge of the protease substrate and protease inhibitorstructures led to a “structure-informed” strategy of drug de-velopment. This strategy led to the design of an initial set ofinhibitors that proved that inhibition of HIV-1 protease wouldresult in inhibition of HIV replication [5]. This knowledge hasultimately led to successful drug discovery by a number ofdifferent research groups [6–8]. These inhibitors are highly po-

Reprints or correspondence: Dr. Joseph J. Eron, Jr., Infectious DiseasesDivision, CB #7030, 547 Burnett-Womack, Univ. of North Carolina atChapel Hill, Chapel Hill, NC 27599-7030 ([email protected]).

Clinical Infectious Diseases 2000;30(Suppl 2):S160–70q 2000 by the Infectious Diseases Society of America. All rights reserved.1058-4838/2000/3006S2-0009$03.00

tent in cell culture assays and highly specific for the HIV-1protease.

Clinical Studies of PIs

The in vitro antiretroviral activity of HIV-1 PIs was quicklyput to the test in clinical trials. In initial studies, the PIs weregiven as single agents in single- or multiple-dose studies, todefine pharmacokinetic parameters of each of the agents andto establish initial in vivo antiretroviral activity. The clinicaldevelopment of PIs coincided with the development of quan-titative amplification assays to measure the amount or copynumber of HIV RNA in blood plasma [9, 10]. Unlike previoustechniques that had been used to measure HIV replication, suchas p24 antigen assays or culture of virus from peripheral bloodmononuclear cells or plasma, which were positive in a minorityof infected patients, these newer techniques enabled the mea-surement of most patients’ HIV-1 RNA levels. These assaysproved to be sensitive measures of both ongoing HIV repli-cation in an infected patient and the inhibition of HIV repli-cation by antiretroviral agents [11, 12]. The measurement ofHIV RNA levels in blood plasma became an essential toolfor assessing antiretroviral activity of new antiretroviral com-pounds and an indicator of the clinical benefits of a treatmentregimen [13].

PIs that were developed initially had poor oral bioavailabilityand were administered through iv infusion. Improvements inthe solubility of these agents enhanced oral bioavailabilityto allow for larger-scale clinical development. Five com-pounds—ritonavir, saquinavir, indinavir, nelfinavir, and am-prenavir [6–8, 14]—have been approved by the US Food andDrug Administration (FDA) for the treatment of HIV-1 infec-tion (table 1). Saquinavir is currently available in 2 formula-

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CID 2000;30 (Suppl 2) HIV-1 Protease Inhibitors S161

Table 1. Currently available protease inhibitors.

Agent Trade name Dosing requirement(s) Dosage Common side effects

Indinavir Crixivan (Merck, West Point, PA) Empty stomach, or with avery light meal

800 mg every 8 h Nephrolithiasis

Nelfinavir Viracept (Agouron, La Jolla, CA) With meals 750 mg 3 times daily;1250 mg twice daily

Diarrhea

Ritonavir Norvir (Abbott Laboratories,Abbott Park, IL)

With or without food, thoughmay be better tolerated withfood

600 mg twice daily;400 mg twice dailyin combination withother protease inhibitor

Nausea, diarrhea, andperioral paresthesias

Saquinavir-HGC Invirase (Roche Labs, Nutley, NJ) With high-fat meals 600 mg 3 times daily GastrointestinalSaquinavir-SGC Fortovase (Roche Labs, Nutley, NJ) With meals (high fat

increases absorption)1200 mg 3 times daily Gastrointestinal

Amprenavir Agnerase (GlaxoWellcome,Research Triangle Park, NC;Vertex Pharmaceuticals,Cambridge, MA)

With or without food 1200 mg twice daily Gastrointestinal,predominantlynausea

NOTE. HGC, hard-gel capsule; SGC, soft-gel capsule.

tions, a hard-gel capsule (HGC; Invirase; Roche Labs, Nutley,NJ) and a soft-gel capsule (SGC; Fortovase; Roche Labs). Thesoft-gel formulation was developed to improve the oral bio-availability of saquinavir. The oral bioavailability of the cur-rently available PIs ranges from 4% for saquinavir-HGC to170% for ritonavir and nelfinavir [3].

The protein binding of PIs to plasma proteins offered anotherobstacle to clinical development. Plasma protein binding, whichoccurs to predominantly 2 proteins, albumin and a1-acid gly-coprotein, ranges from 60% with indinavir to 198% withritonavir, nelfinavir, amprenavir, and saquinavir [3, 15, 16]. Theextent and avidity of protein binding influences the amount offree drug that is available for entry into cells and for clearanceby metabolic pathways. One HIV PI, SC52151, which showedsubstantial antiretroviral activity in vitro, had limited anti-retroviral activity when given orally to HIV-infected patients,at least in part because of tight protein binding [17].

Ritonavir. Initial studies of ritonavir (ABT-538; Norvir;Abbott Laboratories, Abbott Park, IL) demonstrated that thecompound had antiretroviral activity over a range of doseswhen administered as a single agent [18, 19]. A clear dose-response relationship was observed, with the highest dose level(600 mg twice daily) associated with the most durable anti-retroviral response. Doses of ritonavir higher than this provedintolerable [20], and the dosage of 600 mg twice daily waschosen for further development. Ritonavir has a relatively high(198%) degree of protein binding but remains active in vitro inthe presence of human plasma proteins [3].

In the first demonstration of the clinical benefit of PIs, alarge-scale clinical (phase III) trial was undertaken in whichritonavir or placebo was added to the antiretroviral therapy forinfected patients in a blinded fashion. Study patients had ad-vanced HIV disease with CD4 cell counts !100 cells/mL. Onceritonavir was added to their treatment regimens, patients whowere receiving >1 reverse transcriptase inhibitor were also re-ceiving a combination of antiretrovirals; however, because of

the sequential administration of the ritonavir, these patientswere functionally receiving ritonavir monotherapy. Despite thefact that patients had very advanced HIV disease, the additionof ritonavir had a remarkable effect on both mortality andprogression to AIDS-defining complications [21]. Over a me-dian follow-up of 29 weeks, the addition of ritonavir resultedin a 47% reduction in occurrences of AIDS-defining events ordeath.

Indinavir. Initial clinical studies of indinavir sulfate (MK-639; Crixivan; Merck, West Point, PA) demonstrated thatplasma concentrations that exceeded the 95% inhibitory con-centration (IC95) for HIV-1 in cell culture were achievable [22].The agent is not tightly bound by human plasma [8], and, inHIV-1–infected patients given 600 mg of indinavir 3 times aday, mean peak concentrations and mean trough concentra-tions of approximately 50 and 3 times the in vitro IC95, re-spectively, for clinical isolates were achieved [23]. Indinavirdemonstrated a dose-response effect [24, 25] with the mostpotent antiretroviral activity at 2400 mg/d, as measured bychanges in HIV-1 RNA levels [23, 26]. Daily doses 12400mg/d did not appear to increase the antiretroviral effect [26].

Multiple larger studies included an indinavir monotherapyarm [27–30]. All showed similar findings for indinavir mono-therapy, which was uniformly potent, with decreases in HIV-1RNA ranging from 1.5 log10 copies/mL to 3.1 log10 copies/mLover 12–24 weeks, when a lower limit of quantification of400–500 copies/mL was used. However, sustained responses(i.e., HIV-1 RNA level below quantifiable limits for 6 months)were seen in only ∼40% of patients in each study. Although useof PI monotherapy is neither logical nor recommended [31],this degree of success with indinavir as a single agent speaksto the overall potency of this agent. Another potentially im-portant characteristic of indinavir is its penetration into theCNS and CSF.

Saquinavir. Saquinavir (Invirase; saquinavir-HGC) in itsoriginal formulation has a bioavailability of ∼4% when given

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with a high-fat meal. Concentrations are decreased ∼5-fold ifsaquinavir is given in the fasting state. The low bioavailabilityis, in part, due to extensive first-pass metabolism in the intestinalwall and the liver by the cytochrome p450 enzyme system. Sa-quinavir-HGC was studied as monotherapy in HIV-1–infectedmen who had minimal symptoms related to their disease, hadCD4 cell counts !500 cells/mL, and had received no previousantiretroviral therapy [32]. In this trial, patients received 25, 75,200, or 600 mg 3 times a day for 16 weeks. The highest dose,600 mg 3 times a day, produced a peak median decrease in HIV-1 RNA of 80% (or ∼0.7 log10 copies/mL).

Higher doses of saquinavir-HGC have been tested. A dosageof 3600 mg/d resulted in a maximal mean decrease in plasmaHIV RNA level of 1.06-log RNA copies/mL, and, at week 24,the plasma HIV RNA level remained at 0.48-log RNAcopies/mL lower than baseline. A higher dose of saquinavir(7200 mg/d) produced a mean maximal decrease in the plasmaHIV RNA level of 1.34-log RNA copies/mL, and, at week 24,the plasma HIV RNA level remained 0.85-log RNA copies/mLlower than at baseline. Higher plasma drug concentrations inindividual patients correlated with greater reductions in plasmaHIV RNA levels over the 2 doses [33]. However, the higherdose (7200 mg/d) requires the ingestion of 36 capsules per day.

Saquinavir-SCG (Fortovase) is a more bioavailable formu-lation of saquinavir. This formulation has been tested only incombination with other agents, although the potency of sa-quinavir-SGC would be expected to be greater than that of thehard-gel formulation because of improved bioavailability. Sa-quinavir-SGC has a greater bioavailability than saquinavir-HGC, but the recommended dose is twice as high (1200 mg3 times daily), which results in substantially higher plasma con-centrations with the newer formulation.

Nelfinavir. Nelfinavir mesylate (Viracept; Agouron, LaJolla, CA) has an oral bioavailability 175% and high proteinbinding [3]. Nelfinavir has a half-life of ∼4 h and, when givenat a dosage of 750 or 1000 mg 3 times a day, trough concen-trations remain above the IC95 of nelfinavir for wild-type HIVin the presence of a1-acid glycoprotein. There is a dose responsewith respect to effects of nelfinavir on HIV-1 RNA and CD4cell counts at dosages from 500 mg twice daily to 1000 mg 3times daily. Doses of 750 mg twice daily or less resulted in adecline in antiviral activity over 28 days, following a peak effectat 14 days [34]. Patients treated with 750 or 1000 mg 3 timesdaily had an antiviral effect >1.5 log10 over 28 days, and 60%of patients had RNA levels fall below the detection limit of500 copies/mL. However, in contrast to indinavir recipients,virtually all patients who continued nelfinavir monotherapyafter 28 days had HIV RNA levels return to or surpass theirpretherapy HIV-1 RNA levels [34].

Amprenavir. Amprenavir is the most recently approvedPI in the United States. Amprenavir (GW-141, Vertex-478;GlaxoWellcome, Research Triangle Park, NC; Vertex Phar-maceuticals, Cambridge, MA) has high potency in vitro [35],

a long half-life of 7–9.5 h, and an oral bioavailability that isunaffected by food [36]. The protein binding of this compound,when these proteins are present in physiological concentrations,has not been great [15, 16]. However, higher concentrations ofa1-acid glycoprotein may have a substantial effect on the ac-tivity of amprenavir [15].

Amprenavir has been administered as monotherapy in 2 clin-ical trials. In 1 trial, amprenavir therapy resulted in an ∼2-log10

decrease in HIV-1 RNA plasma levels over 28 days of therapy,with use of a limit of quantification of 400 copies/mL [37].However, in a larger trial that compared amprenavir mono-therapy with amprenavir/lamivudine/zidovudine combinationtherapy, the antiretroviral effect of amprenavir monotherapydiminished quickly in a substantial minority of patients. Aftera median follow-up of 88 days, the HIV RNA levels in morethan one-third of patients returned to baseline or were 110-foldhigher than the nadir values [14]. Only 26% of patients whoreached 12 weeks of amprenavir monotherapy had HIV-1 RNAlevels below the limit of quantification, at 500 copies/mL.

PIs in Combination Therapy

The use of combinations of nucleoside analogues and theuse of PIs as monotherapy or added to a failing regimen havebeen shown to have substantial antiretroviral activity and clin-ical benefit [21, 38–41]. Each of the PIs currently available hasbeen shown to have potent antiretroviral activity when givenas a single agent and, as is the case with ritonavir, to haveclinical benefit [21]. However, PI monotherapy would be ex-pected to result in evolution of resistant virus and loss ofantiretroviral effect in most patients. Currently, the goal ofantiretroviral therapy is to suppress HIV-1 replication to thegreatest extent possible, that is, below the detectable limits ofthe most sensitive assays available [31, 42]. Suppression of rep-lication below the limits of detection is associated with moredurable suppression of plasma HIV-1 RNA levels. The initia-tion of therapy with multiple agents is now the recommendedstandard for achieving this result [31, 43].

PIs in combination with nucleoside reverse transcriptase in-hibitors (NRTIs). The use of a potent PI in combinationwith 2 nucleoside agents has become one of the recommendedstandard therapy for previously treatment-naive HIV-infectedpatients [31, 43]. A substantial body of information exists onthe effects of PI combination regimens on HIV viral load andon clinical improvement and survival [2]. Each of the currentlyapproved PIs has been tested in combination with nucleosideanalogues in >1 clinical trials.

One of the first studies to demonstrate the profound effectsof a PI plus 2 NRTIs on HIV-1 RNA levels compared indinavir/lamivudine/zidovudine with indinavir alone and with zidovu-dine/lamivudine [29, 44, 45]. In this study, the triple-drug com-bination resulted in a decrease in HIV RNA levels to belowthe limit of quantification of 500 copies/mL in 180% of patients

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at 6 months of treatment. This level of effectiveness has per-sisted in the patients initially treated with triple-drug therapyfor 1148 weeks [44, 45]. This study used an intent-to-treat anal-ysis, in which all patients were included unless they left thestudy for nontreatment-related reasons, in which case they werethen excluded from the analysis (2 of 32 patients over 148weeks).

Two-thirds of patients who received indinavir/lamivudine/zi-dovudine from the outset had HIV RNA levels !50 copies/mLafter 148 weeks. Indinavir, lamivudine, and zidovudine have alsobeen shown to have potent effects on HIV-1 RNA levels andCD4 cell counts in patients with very advanced HIV diseasewhose CD4 cell counts were !50 cells/mL [30]. Similar potentresults were seen with indinavir combined with didanosine andzidovudine [28]. Indinavir has been combined with lamivudineand stavudine [46] and with didanosine and stavudine [47] inclinical trials. In each of these studies, the triple-drugcombinationwas compared with indinavir/lamivudine/zidovudine. The effectson HIV RNA plasma levels of the combination of indinavir withlamivudine/stavudine and with didanosine/stavudine were almostidentical to those of indinavir/lamivudine/zidovudine. The pro-portions of patients whose HIV RNA levels decreased to !500copies/mL at 48 weeks in an intent-to-treat analysis, in whichany missing data are considered a treatment failure, were alsovery similar with each of the 3 indinavir-including triple-drugcombinations.

The triple combination of indinavir with 2 nucleoside ana-logues has also been shown to improve survival and to delayHIV-1 disease progression [48]. In the AIDS Clinical TrialsGroup (ACTG) Study 320, patients with CD4 cell counts !200cells/mL who had received zidovudine and other nucleosidesbut not lamivudine or PIs were randomized to receive eitherzidovuine plus lamivudine or the triple-drug combination ofzidovudine, lamivudine, and indinavir. The addition of lami-vudine to zidovudine-including regimens had been shownto improve survival rates and to delay disease progressionin a recently completed trial [41]. Despite this fact, the triple-drug regimen of zidovudine/lamivudine/indinavir resulted in amarked improvement in survival rates and a significant delayin HIV-1 disease progression, compared with zidovudine/lamivudine. The relative risks of death and disease progressionwere both improved by 150% [48].

When the virologic data from this trial were examined, theantiretroviral effectiveness of the triple combination was lessthan that seen in previous studies [49]. Demeter et al. [49] dem-onstrated that only about half of the patients in this trial treatedwith indinavir/lamivudine and zidovudine had HIV RNA levelsdecrease and remain below detectable limits after 48 weeks. Inthe subgroup of patients who had CD4 cell count !50 cells/mLat the time of enrollment, the proportion of patients with HIVRNA levels below quantifiable limits (500 copies/mL) at 48weeks was !40%. For approximately half of those patients,HIV-1 could still be cultured from their peripheral blood mon-

onuclear cells by use of a simple coculture assay. These resultssuggest that triple-drug therapy with a PI and 2 nucleosideanalogues may not produce the desired antiviral result for amajority of patients with low CD4 cell counts.

The use of nelfinavir in combination with zidovudine andlamivudine in treatment-naive patients also resulted in sup-pression of HIV RNA to !500 copies/mL in 75% of the patientsover 6 months [50]; this activity also seemed to persist overtime. Two dosages of nelfinavir were used in this study. Nel-finavir at a dosage of 750 mg 3 times daily had the more pro-found and durable effect on HIV-1 RNA levels in plasma, com-pared with the effect of 500 mg 3 times daily. Nelfinaviradministered at a dose of 1250 mg twice daily has been com-pared with a 3-times-daily dose of 750 mg, each combined withlamivudine and stavudine, and was shown to have similar an-tiretroviral activity [51]. Twice-daily nelfinavir is now commonlyused.

Saquinavir-SGC appears to be more potent that saquinavir-HGC [52] and to have potency and antiretroviral efficacy sim-ilar to those of indinavir when either drug is combined withzidovudine and lamivudine [53]. Saquinavir-SGC given as 1600mg twice a day has now been compared with the 1200-mg3-times-daily dose, both combined with 2 nucleoside analogues[54]. These 2 dosing strategies appear similarly effective; in∼60% of patients, an HIV-1 RNA level !400 copies/mL wasachieved in an intent-to-treat analysis. However, the final anal-ysis of this study, which will occur when all patients reach week48, is not complete.

Amprenavir has also been studied in combination with nu-cleoside analogues. Amprenavir in combination with lamivu-dine and zidovudine was compared with amprenavir mono-therapy [14]. The triple-therapy arm was found to be superiorto monotherapy. At 24 weeks, 63% of patients who were stillreceiving therapy and could be evaluated (an as-treated anal-ysis) were found to have !500 copies/mL. These results aresimilar to those of a second comparative trial, in which am-prenavir/lamivudine/zidovudine was compared with lamivudineand zidovudine [55]. The triple-drug regimen was superior tothe dual-nucleoside regimen.

In an intent-to-treat analysis of the proportion of patientswith HIV RNA levels !400 copies/mL, in which any missingvalue is considered to be 1400 copies/mL, 41% of patientstreated with amprenavir/lamivudine/zidovudine were observedto have !400 copies/mL [55]. Amprenavir has also been com-bined with a single nucleoside, abacavir. This combination hasbeen shown to have potent activity in patients with early stageHIV disease (1400 CD4 cells/mm3), with 40% having HIV RNAlevels !5 copies/mL at 48 weeks in an intent-to-treat analysis[56].

>2 PIs in combination. Each of the currently available PIshas limitations that decrease the usefulness of these agents or,at best, make long-term adherence to them challenging. Someof these limitations include low bioavailability, short half-lives,

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toxicity, food requirements for administration, and potentiallylimited potency. In addition, single PIs with 2 NRTIs may nothave adequate potency in all circumstances, as outlined above.Some of the limitations of PI potency may be due to inadequateexposure of HIV to the inhibitor.

The best example of this concept is the PI saquinavir, witha bioavailability of 4%–20%, depending on the drug formu-lation. Optimal exposure to saquinavir—indeed, probably toany of the currently available PIs—is limited by bioavailability,protein binding, drug half-life, formulation (i.e., pill number,size, and dose frequency), and/or toxicity. The use of 2 PIs incombination has been proposed as a way to overcome some ofthese limitations. Combining PIs may improve bioavailabilityand reduce dosing frequency through pharmacokinetic inter-actions. Even if there are no pharmacokinetic interactions, theuse of 2 PIs may increase overall exposure to PI concentrations,if full doses of the 2 PIs are administered and if they do nothave substantial overlapping toxicity. However, if there is nosubstantial pharmacokinetic interaction between the 2 agents,the number of doses of medications and the number of pillsconsumed may be quite high. The cost of such regimens mightalso be prohibitively high.

Multiple-PI combinations are under active study in clinicalresearch trials. Ritonavir-including dual-PI combinations ap-pear to have the most favorable pharmacokinetic interactions.The combination of ritonavir and saquinavir has been the mostextensively studied. Ritonavir dramatically enhances the phar-macokinetic profile of saquinavir by inhibiting the P450-mediated metabolism of saquinavir in the gut and liver. Inaddition, 400 mg of ritonavir coadministered with saquinavirincreases saquinavir levels by 20- to 50-fold [57].

The combination of ritonavir and saquinavir has been stud-ied in a randomized trial that involved PI-naive patients [58].Several different doses of ritonavir and saquinavir were used.At 48 weeks, 60% of all patients had HIV RNA levels !200copies/mL in an intent-to-treat analysis. Approximately one-quarter of these patients had nucleoside analogues added totheir regimens after 12 weeks of administration of ritonavir/saquinavir alone. Ritonavir (400 mg) and saquinavir (400 mg),both administered twice daily, were the most tolerable doses.

Liver function abnormalities occurred more commonly inpatients who had underlying hepatitis B or C. Diarrhea, as-thenia, perioral paresthesias, and nausea were the most com-mon adverse events at these doses. The potential for limitedpenetration of these 2 agents into other tissue compartments,such as the male genital tract and the CNS, has been increasedas a concern with regard to this treatment combination [59,60].

Ritonavir has also been studied in combination with nelfi-navir and indinavir. When 400 mg of ritonavir twice daily wasgiven in combination with nelfinavir at doses of either 500 or750 mg twice daily, the area-under-the-curve (AUC) concen-tration for nelfinavir was similar to that seen with the approved

dose of nelfinavir (750 mg 3 times daily). With the higher dosesof nelfinavir, the AUC concentration of M8 (the active metab-olite of nelfinavir) are raised even further [61]. The antiretroviraleffect of this combination was substantial in the small numberof patients studied [62]. Moderate to severe diarrhea wasa common side effect, seen in almost half of the 20 patientstreated.

Indinavir, although potent, has practical limitations. The rec-ommended dosing is 800 mg every 8 h on an empty or near-empty stomach. However, when 400 mg of indinavir is givenwith 400 mg of ritonavir, both twice daily, AUC measurementsare almost identical, and higher trough concentrations andlower peak concentrations occur than with indinavir alone,given at 800 mg every 8 h. These results are seen even whenthe ritonavir/indinavir combination is administered with a meal[63].

The antiretroviral effect of this combination has only beenstudied in a small number of patients, but 18 of 18 treatment-naive patients receiving ritonavir/indinavir plus lamivudine andstavudine had HIV RNA levels !400 copies/mL after 12 weeksof therapy [64]. The duration of study has so far precluded adetailed examination of adverse events. Indinavir has now beenstudied with ritonavir in several different dose combinations[65, 66]. Each combination increased indinavir trough levels15- to 35-fold. Combinations of indinavir (800 mg) with either100 mg or 200 mg of ritonavir and indinavir (400 mg) withritonavir (400 mg) are all undergoing additional study.

Indinavir has also been studied with nelfinavir in a smallphase I/II pharmacokinetic trial. Indinavir (1000 mg) and nel-finavir (750 or 1000 mg) given every 12 h resulted in steady-state indinavir levels similar to those with every-8-h dosing, butthe trough concentrations of nelfinavir were low, and diarrheawas a common side effect [67]. The combination of indinavir(1200 mg) with nelfinavir (1250 mg), both given twice daily,yields the most favorable trough levels and appears to havepotent antiretroviral activity [68].

Nelfinavir combined with saquinavir has been studied in smallpharmacokinetic trials and in a larger antiretroviral-efficacy trial.Single-dose studies suggested that nelfinavir would increase sa-quinavir levels by ∼5-fold [69], although the effect in differentpatients was quite variable. However, the effects of nelfinavir onsaquinavir concentrations over the long term may be less marked.In a larger study, patients randomized to receive saquinavir-SGC(800 mg 3 times daily) and nelfinavir (750 mg 3 times daily) hada relatively modest antiretroviral response [70]. The proportionof patients with HIV-1 RNA levels !50 copies/mL over time wassimilar or less than the proportion seen with either a PI aloneor a PI with 2 nucleosides.

This dual-PI combination given with 2 NRTIs had the mostpotent antiretroviral effect in this study. Twice-daily dosing withthe nelfinavir/saquinavir combination may be possible, but thepill number is high and a large majority of patients have somediarrhea. Nelfinavir (1250 mg) with saquinavir-SGC (1200 mg)

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twice daily, combined with 1 nucleoside analogue, has activitysimilar to saquinavir-SGC with 2 nucleoside analogues [54].

Amprenavir has been studied in combination with indinavir,nelfinavir, or saquinavir, to obtain pharmacokinetic and pre-liminary antiretroviral activity data [71]. Each compound wasadministered 3 times daily. Indinavir and nelfinavir were givenat their approved dosages, and saquinavir-SGC was adminis-tered at a dosage of 800 mg 3 times daily, as was amprenavir.Preliminary results show potent activity for each of the com-binations, although patient numbers were small [71]. Nomarked pharmacokinetic interactions were seen. Only 1 patienthas withdrawn from this study, because of an adverse eventthat occurred during the first 24 weeks of study.

The pharmacokinetic interaction of amprenavir with rito-navir has recently been studied, and 200 mg of ritonavir wasfound to increase amprenavir trough levels significantly.

Overall, combinations of 2 PIs appear to increase potencyover single-PI therapy, although head-to-head comparisons of2-PI regimens with single-PI regimens have yet to show dra-matic differences [70, 72]. However, many of these combina-tions require large numbers of pills each day, and the side-effectprofile and cost of some regimens may become significant con-siderations. Ritonavir-based dual-PI combinations seem tohave the most favorable pharmacokinetics, allowing for de-creased pill numbers and cost without reducing potency.

PIs in combination with nonnucleoside reverse transcriptase in-hibitors (NNRTIs). PIs have been combined with NNRTIs,both with and without coadministration of NRTIs. To date, moststudies of PI/NNRTI/NRTI combinations have been as salvageregimens for NRTI or NRTI/PI treatment failures (see below).When given without NRTIs, the combination of indinavir andefavirenz resulted in HIV RNA levels !400 copies/mL in a sub-stantial proportion (80%) of patients who continued receivingtherapy (as-treated analysis) in 2 relatively large clinical trials [73,74]. Nelfinavir has also been combined with efavirenz, producingsimilar results after 16 weeks [75]. The use of combination PI/NNRTI regimens with or without NRTIs as initial therapy maylimit subsequent treatment options for patients who do not re-spond completely to therapy or who relapse during therapy.

Treatment of Patients Whose Initial PI Therapy Fails

PIs are clearly an important component of effective salvagetherapy for patients who have not responded to nucleosideanalogue therapy. Indinavir in combination with lamivudineand zidovudine has been shown to be highly effective for pa-tients who have had extensive zidovudine treatment [29, 44]and for patients who have had experience with multiple nucle-oside analogues, as long as they are lamivudine-naive [48]. Thecombination of PI with NNRTIs and nucleosides has also beenused successfully as salvage therapy for patients who have hadextensive NRTI treatment [76, 77].

For patients who have persistent or recurrent evidence of

HIV replication during therapy with NNRTIs in combinationwith nucleoside analogues, the use of a combination includinga PI also seems to be effective as salvage therapy, althoughstudies have had only short follow-up periods [78, 79]. A goodresponse to PI-based therapy after therapy directed only at thereverse transcriptase enzyme is theoretically plausible.

Successful treatment options are needed for patients whoseHIV-1 RNA levels have not fallen below detection limits orhave rebounded to above these limits during initial therapy withPI-including regimens. The use of indinavir or ritonavir afterprolonged saquinavir therapy had only modest antiretroviraleffect [80, 81]. The use of saquinavir in an incompletely sup-pressive regimen appears to predispose to indinavir resistance,even if resistance mutations cannot be documented when ther-apy is changed. The failure of single-PI therapy after failure oftherapy with another PI is not surprising, given the substantialdegree of cross-resistance between PIs [82, 83]. Cross-resistanceseems greatest if the virus has a high level of resistance to 1inhibitor.

Dual-PI therapy with >1 agent to which virus from the pa-tient would be expected to be susceptible is commonly used assalvage therapy after PI failure. The combination of ritonavirand saquinavir has been used with variable success to treatpatients whose single-PI–including regimens have failed[84–86]. Following nelfinavir-including regimens, treatmentwith ritonavir/saquinavir in combination with lamivudine andstavudine resulted in HIV RNA levels !400 copies/mL in 65%of patients after 6 months of therapy, in an intent-to-treat anal-ysis [87].

Initial resistance to nelfinavir may result predominantly froma single-point mutation that conveys limited cross-resistance toother PIs [7, 34, 88, 89]. Ritonavir plus saquinavir-based reg-imens appear to be less successful after initial failure of anindinavir- or ritonavir-including regimen, in part because of theoccurrence of resistance at the time of the switch [84, 86]. How-ever, changing from the initial therapy early after the detectionof HIV-1 RNA in plasma (i.e., early virologic failure) mayenhance the response to subsequent dual-PI regimens.

In a retrospective study, an early switch from an indinavir-including regimen to a ritonavir/saquinavir–based regimen re-sulted in 56% of patients having sustained HIV RNA levels!400 copies/mL [90]. Earlier switching from an indinavir-including regimen to a salvage regimen may limit the degree ofcross-resistance between the initial PI regimen and the salvageregimen [82, 91]. Adding an NRTI to a dual PI salvage regimenmay be another way to improve response rates to PI salvageregimens in those patients who are naive to NNRTI therapy[92, 93].

PIs in Development

PIs that are approved by the FDA have demonstrated potentantiretroviral activity and/or clinical benefits. However, they

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have limitations collectively and individually, involving (forsome or all of the currently available PIs) bioavailability, largepill numbers, dosing frequency, dosing schedule with meals, andtoxicity. Potential cross-resistance among available PIs is animportant issue, and the success of salvage treatment of patientswhose treatment with a PI has failed is by no means guaranteed.Development of additional PIs that address some or all of theseissues is essential.

ABT-378. ABT-378 is a peptidomimetic PI that is ∼10 timesmore active than ritonavir in vitro [94] and has in vitro activityagainst HIV variants that have decreased susceptibility to rito-navir [95, 96]. This agent is extensively metabolized by the P4503A4 system, and its catabolism is substantially inhibited by ri-tonavir. When ABT-378 is administered with ritonavir to rats,the AUC is increased 13-fold and the half-life is increased sub-stantially [97]. In HIV-1–seronegative volunteers, ABT-378 giventwice daily with as little as 50 mg or 100 mg of ritonavir resultedin trough drug concentrations 20- to 80-fold greater than the IC50

of ABT-378 when tested against wild-type HIV-1 in vitro in thepresence of plasma proteins [98]. ABT-378 is 198% protein-boundat protein concentrations in the physiological range [98].

This inhibitor combined with either 100 mg or 200 mg ofritonavir (ABT-378/r) has been studied with lamivudine and sta-vudine in 100 antiretroviral-naive patients. In an intent-to-treatanalysis, 79% of patients had HIV RNA levels !50 copies/mLafter 36 weeks of therapy. No patient discontinued therapy be-cause of an adverse event related to the drug [99]. ABT-378,because of its activity against ritonavir-resistant isolates [96], isalso being tested as a component of salvage therapy for cases inwhich virologic failure occurs during treatment with a PI. Patientswho had HIV-1 RNA levels 11000 copies/mL after at least 3months of treatment with a single-PI–including regimen weregiven the combination of ABT-378/r with nevirapine and a least1 new nucleoside agent [99]. In an intent-to-treat analysis, 67%of these patients had an HIV RNA level !400 copies/mL at 36weeks of therapy. Phase III studies of ABT-378/r that involvetreatment-naive and PI-experienced patients are ongoing.

Tipranavir. Tipranavir (PNU-140690) is the first nonpep-tidic HIV PI to reach clinical development. This agent has beengiven to HIV-seronegative patients at doses ranging from 300mg to 2000 mg as a single dose and then 3 times a day. Dosesof 900 mg 3 times daily or greater produced trough concen-trations 11 mmol, the IC90 for wild-type HIV-1 to PNU-140690in vitro [100]. This agent has good activity in vitro, is synergisticwith NRTIs and NNRTIs, and appears to be active in vitroagainst HIV-1 variants that have decreased susceptibility to thecurrently approved PIs [101]. Tipranavir also shows additiveto synergistic activity with ritonavir in vitro, even against ri-tonavir-resistant isolates [102].

Preliminary data from patients who had never received a PIshowed single-agent tipranavir activity, with decreases in HIV-1plasma RNA ranging from 1.0 to 1.5 log10 over an 11-day period,as revealed by an HIV-1 RNA assay with a lower limit of quan-

tification of 400 copies/mL. A dose response was seen, with thehighest dose (1500 mg 3 times daily) yielding the greatest activity.No serious adverse events were seen in this early phase I/II study.An analysis after 12 weeks revealed no distinct mutationalpatternsuggestive of resistance development.

This agent appears to require dosing 3 times a day, and, withthe current formulation, the 1500-mg dose requires 10 capsules3 times daily. Therefore, if tipranavir is active against protease-resistant HIV-1, this agent may be reserved for PI-experiencedpatients.

Additional PIs are in development. Two promising com-pounds are BMS-232632 and AG-1776. BMS-232632 is an aza-peptide PI with potent in vitro activity, even in the presence ofhuman serum proteins. This drug retains activity in vitro againstHIV-1 variants resistant to other PIs [103]. The pharmacoki-netics of this compound may also allow for once-daily dosing[104]. AG-1776 is also highly active in vitro. Clinical isolatesof HIV-1 from patients whose treatment with regimens thatinclude indinavir, nelfinavir, ritonavir, or saquinavir have failedto retain susceptibility to AG-1776 [105]. Recombinant viralstrains with multiple mutations in the protease gene that arehighly resistant to currently available PIs were also inhibitedin vitro by AG-1776 [105]. Initial pharmacokinetic studies ofthis compound are under way.

Adverse Effects

Each of the approved PIs has a relatively distinct side-effectprofile, which may limit therapy (table 1). Ritonavir causesnausea, vomiting, diarrhea, and perioral paresthesias. Indinavirincreases serum bilirubin levels predominantly by increasing theindirect fraction. Indinavir administration also leads to ne-phrolithiasis or urinary tract sludging in 5%–15% of treatedpatients. Saquinavir is associated with gastrointestinal com-plaints, and nelfinavir causes diarrhea in a substantial propor-tion of patients, although the diarrhea is commonly self-limited.Amprenavir is also associated with nausea and perioral par-esthesias and can cause rash. Frequently, each of these sideeffects can be managed with supportive therapy or occasionallyby the exchange of 1 PI for another.

Recently, however, more pervasive side effects that may beclass-specific have been observed. PI therapy is associated withelevated triglyceride levels and, occasionally, increased choles-terol levels. Diabetes has developed in patients treated with PIs,and although this event is uncommon, insulin resistance ap-pears to occur more frequently [106]. Finally, redistribution offatty tissue from subcutaneous to visceral locations, termedlipodystrophy or fat redistribution syndrome, has been reportedto occur in patients receiving PIs [106, 107]. Although this phe-nomenon occurred before the introduction of PI into anti-retroviral therapy, its frequency appears to be greater with theseagents.

A specific interaction of PIs with human proteins involved

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in lipid metabolism has been hypothesized as a mechanism forthis dysregulation [108]. However, clear definition(s) for thissyndrome or syndromes are only now being developed, and thecontribution of long-term nucleoside analogue therapy tochanges in body fat is under investigation [109].

Conclusions

PI therapy for HIV-1–infected patients has radically changedthe expectations for antiretroviral therapy. Clinical improve-ment is now the rule, and the goal of antiretroviral therapy isto attain HIV RNA levels in plasma that are below measurablelimits. Currently, 5 PIs are widely available in North Americaand Europe. These agents are commonly coupled with 2 nu-cleoside analogues, although alternative combinations are fre-quently being used. The combination of 2 PIs also frequentlyresults in potent therapy and, because of pharmacokinetic in-teractions, may enable the dosing frequency to be reduced andtolerability to increase.

Unfortunately, the plasticity of the HIV genome, coupledwith the high failure rate of HIV reverse transcriptase and thepotential for high levels of replication, has led to the emergenceof HIV-1 variants resistant to PIs. The consequences of resis-tance to PIs (and other antiretrovirals) are not yet fully ex-plored, but loss of treatment effects and progression of clinicaldisease have been noted.

Potent antiretroviral regimens are needed for use after in-adequate viral suppression or relapsing viral replication duringuse of PI-including combinations. New PIs in development mayhave better activity against variants resistant to the first gen-eration of PIs, and some may have favorable formulations andpharmacokinetics.

Finally, the newly recognized side effects of PI therapy, suchas hypertriglyceridemia, insulin resistance, and lipodystrophy,must be better characterized. Whether these side effects arecommon to the class or occur more commonly with 1 PI versusanother is not yet clearly known. Despite these caveats, PIsremain one of the backbones of potent antiretroviral therapy.

References

1. Hogg RS, Heath KV, Yip B, et al. Improved survival among HIV-infectedindividuals following initiation of antiretroviral therapy. JAMA 1998;279:450–4.

2. Palella FJ Jr, Delaney KM, Moorman AC, et al. Declining morbidity andmortality among patients with advanced human immunodeficiency virusinfection. HIV Outpatient Study Investigators. N Engl J Med 1998;338:853–60.

3. Flexner C. HIV-protease inhibitors. N Engl J Med 1998;338:1281–92.4. Kohl NE, Emini EA, Schleif WA, et al. Active human immunodeficiency

virus protease is required for viral infectivity. Proc Natl Acad Sci USA1988;85:4686–90.

5. Erickson J, Neidhart DJ, VanDrie J, et al. Design, activity, and 2.8 A crystalstructure of a C2 symmetric inhibitor complexed to HIV-1 protease.Science 1990;249:527–33.

6. Kempf DJ, Marsh KC, Denissen JF, et al. ABT-538 is a potent inhibitor

of human immunodeficiency virus protease and has high oral bioavail-ability in humans. Proc Natl Acad Sci USA 1995;92:2484–8.

7. Patick A, Mo H, Markowitz M, et al. Antiviral and resistance studies ofAG1343, an orally bioavailable inhibitor of human immunodeficiencyvirus protease. Antimicrob Agent Chemother 1996;40:292–7.

8. Vacca JP, Dorsey BD, Schleif WA, et al. L-735,524: an orally bioavailablehuman immunodeficiency virus type 1 protease inhibitor. Proc Natl AcadSci USA 1994;91:4096–100.

9. Mellors JW, Kingsley LA, Rinaldo CR Jr, et al. Quantitation of HIV-1RNA in plasma predicts outcome after seroconversion. Ann Intern Med1995;122:573–9.

10. Mellors J, Rinaldo C, Gupta P, White R, Todd J, Kingsley L. Prognosis inHIV-1 infection predicted by the quantity of virus in plasma. Science1996;272:1167–70.

11. Ho DD, Neumann AU, Perelson AS, Chen W, Leonard JM, MarkowitzM. Rapid turnover of plasma virions and CD4 lymphocytes in HIV-1infection. Nature 1995;373:123–6.

12. Wei X, Ghosh SK, Taylor ME, et al. Viral dynamics in human im-munodeficiency virus type 1 infection. Nature 1995;373:117–22.

13. Saag M, Holodniy M, Kuritzkes D, et al. HIV viral load markers in clinicalpractice. Nature Med 1996;2:625–9.

14. Murphy RL, Gulick RM, DeGruttola V, et al. Treatment with amprenaviralone or amprenavir with zidovudine and lamivudine in adults withhuman immunodeficiency virus infection. AIDS Clinical Trials Group347 Study Team. J Infect Dis 1999;179:808–16.

15. Lazdins JK, Mestan J, Goutte G, et al. In vitro effect of a1-acid glycoproteinon the anti–human immunodeficiency virus (HIV) activity of the proteaseinhibitor CGP 61755: a comparative study with other relevant HIV pro-tease inhibitors. J Infect Dis 1997;175:1063–70.

16. Livington DJ, Pazhanisamy S, Porter DJ, Partaledis JA, Tung RD, PainterGR. Weak binding of VX-478 to human plasma proteins and implica-tions for anti–human immunodeficiency virus therapy. J Infect Dis 1995;172:1238–45.

17. Fischl MA, Richman DD, Flexner C, et al. Phase I/II study of the toxicity,pharmacokinetics, and activity of the HIV protease inhibitor SC-52151.J Acquir Immune Defic Syndr Hum Retrovirol 1997;15:28–34.

18. Markowitz M, Saag M, Powderly WG, et al. A preliminary study of rito-navir, an inhibitor of HIV-1 protease, to treat HIV-1 infection. N EnglJ Med 1995;333:1534–9.

19. Danner SA, Carr A, Leonard JM, et al. A short-term study of the safety,pharmacokinetics, and efficacy of ritonavir, an inhibitor of HIV-1 pro-tease. European-Australian Collaborative Ritonavir Study Group.N Engl J Med 1995;333:1528–33.

20. Hicks CB, Lehman L, Eron JJ Jr, et al. Safety and efficacy of ritonaviradministered at two potentially maximum tolerated doses [abstract 415].In: Proceedings of the 11th International Conference on AIDS (Van-couver), 1996.

21. Cameron DW, Heath-Chiozzi M, Danner S, et al. Randomised placebo-controlled trial of ritonavir in advanced HIV-1 disease. Advanced HIVDisease Ritonavir Study Group. Lancet 1998;351:543–9.

22. Teppler H, Pomerantz R, Bjornsson T, et al. Pharmacokinetics and toler-ability studies of L-735,524, a new HIV protease inhibitor [abstract 152].In: Proceedings of the 1st National Conference on Human Retrovirusesand Related Infections. Alexandria, VA: Foundation for Retrovirologyand Human Health, 1993.

23. Stein DS, Fish DG, Bilello JA, Preston SL, Martineau GL, Drusano GL.A 24-week open-label phase I/II evaluation of the HIV protease inhibitorMK-639 (indinavir). AIDS 1996;10:485–92.

24. Deutsch P, Teppler H, Squires K, et al. Antiviral activity of L-735,524, anHIV protease inhibitor, in infected patients [abstract 60]. In: Programand abstracts of the 34th International Conference on AntimicrobialAgents and Chemotherapy. Washington, DC: American Society for Mi-crobiology, 1994.

25. Mellors J, Steigbigel R, Gulick R, et al. A randomized double blind study

Dow





of the oral 4 HIV protease inhibitor, L-735,524 vs. zidovudine (ZDV)in p24 antigenemic, HIV-1–infected patients with less than 500 CD4 cells/mm3 [abstract 88]. In: Program and abstracts of the National Conferenceon Human Retroviruses and Related Infections. Alexandria, VA: Foun-dation for Retrovirology and Human Health, 1995.

26. Steigbigel RT, Berry P, Mellors J, et al. Efficacy and safety of the HIVprotease inhibitor indinavir sulfate (MK 639) at escalating doses [abstract80]. In: Program and abstracts of the 3d Conference on Retrovirusesand Opportunistic Infections. Alexandria, VA: Foundation for Retro-virology and Human Health, 1996.

27. Massari F, Staszewski S, Berry P, et al. A double-blind, randomized trialof indinavir (MK-639) alone or with zidovudine vs. zidovudine alone inzidovudine-naive patients [abstract LB-6]. In: Program and abstracts ofthe 35th International Conference on Antimicrobial Agents and Che-motherapy. Washington, DC: American Society for Microbiology, 1995.

28. Massari F, Conant M, Mellors J, et al. A phase II open-label, randomizedstudy of the triple combination of indinavir, zidovudine (ZDV) and di-danosine (ddI) versus indinavir alone and zidovudine/didanosine in an-tiretroviral naive patients [abstract 90]. In: Program and abstracts of the3d Conference on Retroviruses and Opportunistic Infections (Washing-ton, DC). Alexandria, VA: Foundation for Retrovirology and HumanHealth, 1996.

29. Gulick RM, Mellors JW, Havlir D, et al. Treatment with a combination ofindinavir, zidovudine and lamivudine in HIV-1–infected adults with priorantiretroviral use. N Engl J Med 1997;337:734–9.

30. Hirsch M, Steigbigel R, Staszewski S, et al. A randomized, controlled trialof indinavir, zidovudine, and lamivudine in adults with advanced humanimmunodeficiency virus type 1 infection and prior antiretroviral therapy.J InfectDis 1999;180:659–65.

31. Carpenter C, Cooper DA, Fischl M, et al. Antiretroviral therapy in adults:

updated recommendations of the International AIDS Society–USA

Panel. JAMA 2000;283:381–90.

32. Kitchen VS, Skinner C, Ariyoshi K, et al. Safety and activity of saquinavir

in HIV infection. Lancet 1995;345:952–5.

33. Schapiro JM, Winters MA, Stewart F, et al. The effect of high-dose sa-

quinavir on viral load and CD41 T-cell counts in HIV-infected patients.

Ann Intern Med 1996;124:1039–50.

34. Markowitz M, Conant M, Hurley A, et al. A preliminary evaluation of

nelfinavir mesylate, an inhibitor of human immunodeficiency virus

(HIV)–1 protease, to treat HIV infection. J Infect Dis 1998;177:1533–40.

35. St. Clair M, Millard J, Rooney J, et al. In vitro antiviral activity of 141W94

(VX-478) in combination with other antiretroviral agents. Antiviral Res

1996;29:53–6.

36. Painter GR, St. Clair MH, Demiranda P, et al. An overview of the preclinical

development of the HIV protease inhibitor VX-478 (141W94) [abstract

167]. In: Program and abstracts of the National Conference on Human

Retroviruses and Related Infections. Alexandria, VA: Foundation for

Retrovirology and Human Health, 1995.

37. Schooley R. Preliminary data from a phase I/II study on the safety and

antiviral efficacy of the combination of 141W94 plus 1592U89 in HIV-

infected patients with 150–400 CD41 cells/mm3 [abstract 206]. In: Pro-

gram and abstracts of the 4th Conference on Retroviruses and Oppor-

tunistic Infections. Alexandria, VA: Foundation for Retrovirology and

Human Health, 1997.

38. Eron J, Benoit S, Jemsek J, et al. Treatment with lamivudine, zidovudine

or both in HIV-positive patients with 200–500 CD41 cells per cubic

millimeter. N Engl J Med 1995;333:1662–9.

39. Hammer S, Katzenstein D, Hughes M, et al. A trial comparing nucleoside

monotherapy with combination therapy in HIV-infected adults with CD4

cell counts from 200 to 500 per cubic millimeter. N Engl J Med 1996;

335:1081–90.

40. Katzenstein D, Hammer S, Hughes M, et al. The relation of virologic and

immunologic markers to clinical outcomes after nucleoside therapy in

HIV-infected adults with 200–500 CD4 cells per cubic millimeter. N EnglJ Med 1996;335:1091–8.

41. Anonymous. Randomized trial of addition of lamivudine or lamivudineplus loviride to zidovudine-containing regimens for patients with HIV-1 infection: the CAESAR trial. Lancet 1997;349:1413–21.

42. Centers for Disease Control and Prevention. Report of the NIH panel todefine principles of therapy of HIV infection. MMWR Morb MortalWkly Rep 1998;47(RR-5):1–41.

43. Centers for Disease Control and Prevention. Guidelines for the use of an-tiretroviral therapy in HIV-infected adults and adolescents. MMWRMorb Mortal Wkly Rep 1998;47(RR-5):43–82.

44. Gulick R, Mellors J, Havlir D, et al. Simultaneous vs. sequential initiationof therapy with indinavir, zidovudine, and lamivudine for HIV-1 infec-tion: 100 week follow-up. JAMA 1998;280:35–41.

45. Gulick R, Mellors J, Havlir D, et al. Treatment with indinavir (IDV), zi-dovudine (ZDV) and lamivudine (3TC): three-year follow-up [abstract388]. In: Program and abstracts of the 6th Conference on Retrovirusesand Opportunistic Infections (Chicago). Alexandria, VA: Foundationfor Retrovirology and Human Health, 1999.

46. Gulick R, Squires K, Powderly W, et al. An open-label, randomized, com-parative study of d4T 1 3TC 1 IDV versus ZDV 1 3TC 1 IDV intreatment-naive HIV-infected patients (START I) [abstract 12223]. In:Program and abstracts of the 5th Conference on Retroviruses and Op-portunistic Infections (Chicago). Alexandria, VA: Foundation for Re-trovirology and Human Health, 1998.

47. Eron J, Peterson D, Murphy R, et al. An open-label, randomized, com-parative study of d4T 1 ddI 1 IDV versus ZDV 1 3TC 1 IDV intreatment-naive HIV-infected patients. In: Program and abstracts of the5th Conference on Retroviruses and Opportunistic Infections (Chicago).Alexandria, VA: Foundation for Retrovirology and Human Health,1998.

48. Hammer SM, Squires K, Hughes M, et al. A randomized, placebo-controlledtrial of indinavir in combination with two nucleoside analogues in humanimmunodeficiency virus–infected persons with CD4 cell counts <200 percubic millimeter. N Engl J Med 1997;337:725–33.

49. Demeter L, Hughes M, Fischl M, et al. Predictors of virologic and clinicalresponses to indinavir (IDV)1 ZDV1 3TC or ZDV 1 3TC [abstract409]. In: Program and abstracts of the 5th Conference on Retrovirusesand Opportunistic Infections (Chicago). Alexandria, VA: Foundationfor Retrovirology and Human Health, 1998.

50. Saag M, Knowles M, Chang Y, Chapman S, Clendeninn N, for the ViraceptCooperative Study Group. Durable effect of VIRACEPT (nelfinavir me-sylate, NFV) in triple combination therapy [abstract I-101]. In: Programand abstracts of the 37th Interscience Conference on AntimicrobialAgents and Chemotherapy (Toronto). Washington, DC: American So-ciety for Microbiology, 1997.

51. Petersen A, Johnson M. Long-term comparison of BID and TID dosingViracept (nelfinavir) in combination with stavudine (d4T) and lamivu-dine (3TC) in HIV patients [abstract 12224]. In: Program and abstractsof the 12th Worlds AIDS Conference (Geneva). Geneva: Marathon Mul-timedia, 1998.

52. Thompson M. Activity of soft-gelatin capsule formulation of saquinavir incombination with two nucleosides in treatment-naive HIV-1–seropositivepersons [abstract 12145]. In: Program and abstracts of the 12th WorldAIDS Conference (Geneva). Geneva: Marathon Multimedia, 1998.

53. Boucher C, Borleffs J. Long-term evaluation of saquinavir–soft-gel-capsuleor indinavir as part of combination triple therapy (CHEESE study). In:Program and abstracts of the 12th World AIDS Conference (Geneva).Geneva: Marathon Multimedia, 1998.

54. Cohen C, Mogyoros M, Sands M, et al. TIDBID study: Fortovase (FTV)TID regimen compared to FTV BID or FTV 1 BID regiments in HIV-1–infected patients [abstract 508]. In: Program and abstracts of the 39thInterscience Conference on Antimicrobial Agents and Chemotherapy (SanFrancisco). Washington, DC: American Society for Microbiology 1999.

Dow





55. Goodgame J, Hanson C, Vafidis I, et al. Amprenavir (141W94, APV)/3TC/ZDV exerts durable antiviral acitivity in HIV-1–infected antiretroviraltherapy–naive subjects through 48 weeks of therapy [abstract 509]. In:Program and abstracts of the 39th Interscience Conference on Antimi-crobial Agents and Chemotherapy (San Francisco). Washington, DC:American Society for Microbiology 1999.

56. Bart PA, Rizzardi GP, Gallant S, et al. Combination of I592/141W94 therapyin HIV-1–infected antiretroviral therapy–naive subjects with CD41

counts greater than 400 cells/microliter and viral load greater than 5000copies/mL [abstract 365]. In: Program and abstracts of the 5th Confer-ence on Retroviruses and Opportunistic Infections (Chicago). Alexan-dria, VA: Foundation for Retrovirology and Human Health, 1999.

57. Kempf D, Marsh K, Denissen J, et al. Coadministration with ritonavir en-hances the plasma levels of HIV protease inhibitors by inhibition of cy-tochrome P450 [abstract 79]. In: Program and abstracts of the 3d Con-ference on Retroviruses and Opportunistic Infections (Washington, DC).Alexandria, VA: Foundation for Retrovirology and Human Health, 1996.

58. Cameron DW, Japour AJ, Xu Y, et al. Ritonavir and saquinavir combinationtherapy for the treatment of HIV infection. AIDS 1999;13:213–24.

59. Kravcik S, Gallicano K, Roth V, et al. Cerebrospinal fluid HIV RNA anddrug levels with combination ritonavir and saquinavir. J Acquir ImmuneDefic Syndr 1999;21:371–5.

60. Taylor S, Back D, Workman J, et al. Poor penetration of the male genitaltract by HIV-1 protease inhibitors. AIDS 1999;13:859–60.

61. Flexner C, Hsu A, Kerr B, et al. Steady-state pharmacokinetic interactionsbetween ritonavir (RTV), nelfinavir (NFV), and the nelfinavir activemetabolite M8 (AG1402) [abstract 42265]. In: Program and abstracts ofthe 12th World AIDS Conference (Geneva). Geneva: Marathon Mul-timedia, 1998.

62. Gallant J, Health-Chiozzi M, Anderson R, Fields C, Flexner C. Phase IIstudy of ritonavir-nelfinavir combination therapy: an update [abstract12207]. In: Program and abstracts of the 12th World AIDS Conference(Geneva). Geneva: Marathon Multimedia, 1998.

63. Hsu A, Granneman R, Heath-Chiozzi M, et al. Indinavir can be taken withregular meals when administered with ritonavir. In: Program and ab-stracts of the 12th World AIDS Conference (Geneva). Geneva: MarathonMultimedia, 1998.

64. Workman C, Musson R, Dyer W, Sullivan J. Novel double protease com-binations combining indinavir (IDV) with ritonavir (RTV): results fromfirst study [abstract 22372]. In: Conference record of the 12th WorldAIDS Conference (Geneva). Geneva: Marathon Multimedia, 1998.

65. Saah A, Riddler S, Havlir D, et al. Co-administration of indinavir and nel-finavir: pharmacokinetics, tolerability, antiviral activity, and preliminaryviral resistance [abstract 362]. In: Program and abstracts of the 12th WorldAIDS Conference (Geneva). Geneva: Marathon Multimedia, 1998.

66. Burger DM, Hugen PWH, Prins JM, Van De Ende Me, Reiss P, and LangeJMA. Pharmacokinetics of an indinavir/ritonavir 800/100 mg BID reg-iment [abstract 363]. In: Program and abstracts of the 6th Conferenceon Retroviruses and Opportunistic Infections (Chicago). Alexandria,VA:Foundation for Retrovirology and Human Health, 1999.

67. Saah A, Riddler S, Havlir D, et al. Co-administration of indinavir and nel-finavir: pharmocokinetics, tolerability, anti-viral activity, and preliminaryresistance [abstract 22352]. In: Program and abstracts of the 12th WorldAIDS Conference (Geneva). Geneva: Marathon Multimedia, 1998.

68. Squires K, Riddler S, Havlier D, et al. Co-administration of indinavir (IDV)1200 mg with nelfinavir (NFV) 1250 mg in a twice daily regiment: pre-liminary safety, PK activity [abstract 364]. In: Program and abstracts ofthe 6th Conference on Retroviruses and Opportunistic Infections (Chi-cago). Alexandria, VA: Foundation for Retrovirology and HumanHealth, 1999.

69. Merry C, Barry MG, Mulcahy F, Halifax KL, Back DJ. Saquinavir phar-macokinetics alone and in combination with nelfinavir in HIV-infectedpatients. AIDS 1997;11:F117–20.

70. Moyle G. Study of protease inhibitor combination in Europe (SPICE): sa-

quinavir soft gelatin capsule (SQV-SGC) plus nelfinavir (NFV) in HIV-infected individuals [abstract 12222]. In: Program and abstracts of the 12thWorld AIDS Conference (Geneva). Geneva: Marathon Multimedia, 1998.

71. Eron J, Haubrich R, Richman D, et al. Preliminary assessment of 141W94in combination with other protease inhibitors [abstract 6]. In: Programand abstracts of the 5th Conference on Retroviruses and OpportunisticInfections (Chicago). Alexandria, VA: Foundation for Retrovirology andHuman Health, 1998.

72. Pedersen C, Gerstoft J, Lunnogren J, et al. Saquinavir/ritonavir may havebetter antiviral efficacy than either ritonavir or indinavir in HIV-infectedantiretroviral naive patients [abstract 12221]. In: Program and abstractsof the 12th World AIDS Conference (Geneva). Geneva: Marathon Mul-timedia, 1998.

73. Riddler S, Kahn J, Hicks C, et al. Durable clinical anti–HIV-1 activity (72weeks) and tolerability for efavirenz (DMP 266) in combination withindinavir (IDV) [DMP 266-003, cohort IV] [abstract 12359]. In: Programand abstracts of the 12th World AIDS Conference (Geneva). Geneva:Marathon Multimedia, 1998.

74. Staszewski S, Morales-Ramirez J, Flanigan T, et al. A phase II, multicenter,randomized, open-label study to compare the antiretroviral activity andtolerability of efavirenz (EFV) 1 indinavir (IDV), versus EFV 1 zi-dovudine (ZDV) 1 lamivudine (3TC), versus IDV 1 ZDV 1 3TC at24 weeks [DMP 266-006] [abstract 22336]. In: Program and abstracts ofthe 12th World AIDS Conference (Geneva). Geneva: Marathon Mul-timedia, 1998.

75. Eyster E, Jemsek J, Kagan S, et al. Initial effectiveness and tolerability ofnelfinavir (NFV) in combination with efavirenz (EFV, SUSTIVA, DMP266) in antiretroviral therapy–naive or nucleoside analogue–experiencedHIV-1–infected patients: characterization in a phase II, open-label, mul-ticenter study at 24 weeks [DMP 266-024] [abstract 22386]. In: Programand abstracts of the 12th World AIDS Conference (Geneva). Geneva:Marathon Multimedia, 1998.

76. Harris M, Durakovic C, Conway B, Fransen S, Shillington A, MontanerJS. A pilot study of indinavir, nevirapine, and 3TC in patients withadvanced HIV disease [abstract 475]. In: Program and abstracts of the4th Conference on Retroviruses and Opportunistic Infections (Washing-ton, DC). Alexandria, VA: Foundation for Retrovirology and HumanHealth, 1997.

77. Albrecht M, Katzenstein D, Bosch R, Liou S, Hammer S. ACTG 364:virologic efficacy of nelfinavir (NFV) and/or efavirenz (EFV) in com-bination with new nucleoside analogues in nucleoside-experienced sub-jects [abstract 12203]. In: Program and abstracts of the 12th World AIDSConference (Geneva). Geneva: Marathon Multimedia, 1998.

78. Para M, Weinstock M. Retrospective analysis of protease inhibitor efficacyamong patients failing a delavirdine regimen [abstract 12236]. In: Pro-gram and abstracts of the 12th World AIDS Conference (Geneva). Ge-neva: Marathon Multimedia, 1998.

79. Curry R, Robinson P, Hussain S, Myers M, Robingson P. Retained effec-tiveness of protease inhibitor (PI) therapy (Rx) following “protease spar-ing” nevirapine/nucleoside (NVP/nuc) combination therapy [abstract12231]. In: Program and abstracts of the 12th World AIDS Conference(Geneva). Geneva: Marathon Multimedia, 1998.

80. Para MF, Coombs R, Collier A, et al. Relationship of baseline genotype toRNA response in ACTG 333 after switching from long-term saquinavir(SQVhc) to indinavir (IDV) or saquinavir soft gelatin capsule (SQVsgc)[abstract 511]. In: Program and abstracts of the 5th Conference on Re-troviruses and Opportunistic Infections (Chicago). Alexandria, VA:Foundation for Retrovirology and Human Health, 1998.

81. Mayers DL, Neaton JD, Perez G, et al. Prior saquinavir therapy leads to amodest decrease in subsequent responses to drug regimens containing in-dinavir or ritonavir [abstract 400]. In: Program and abstracts of the 5thConference on Retroviruses and Opportunistic Infections (Chicago). Al-exandria, VA: Foundation for Retrovirology and Human Health, 1998.

82. Condra JH, Schleif WA, Blahy OM, et al. In vivo emergence of HIV-1

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variants resistant to multiple protease inhibitors. Nature 1995;374:569–71.

83. Condra JH, Holder DJ, Schleif WA, et al. Genetic correlates of in vivo viralresistance to indinavir, a human immunodeficiency virus type 1 proteaseinhibitor. J Virol 1996;70:8270–6.

84. Cassano P, Hermans P, Sommereijns B, et al. Combined quadruple therapywith ritonavir-saquinavir (RTV-SQV) 1 nucleosides in patients (p) whofailed in triple therapy with RTV, SQV or indinavir (IDV) [abstract 423].In: Program and abstracts of the 5th Conference on Retroviruses andOpportunistic Infections (Chicago). Alexandria, VA: Foundation for Re-trovirology and Human Health, 1998.

85. de Truchis P, Force G, Zucman D, et al. Effects of a “salvage” combinationtherapy with ritonavir 1 saquinavir in HIV-infected patients previouslytreated with protease-inhibitors (PI) [abstract 425]. In: Program and ab-stracts of the 5th Conference on Retroviruses and Opportunistic Infec-tions (Chicago). Alexandria, VA: Foundation for Retrovirology and Hu-man Health, 1998.

86. Deeks SG, Grant RM, Beatty GW, Horton C, Detmer J, Eastman S. Activityof a ritonavir plus saquinavir–containing regimen in patients with vi-rologic evidence of indinavir or ritonavir failure. AIDS 1998;12:F97–102.

87. Tebas P, Patick AK, Kane EM, et al. Virologic responses to a ritonavir-saquinavir–containing regimen in patients who had previously failednelfinavir. AIDS 1999;13:F23–8.

88. Patick A, Duran M, Cao Y, et al. Genotypic and phenotypic characterizationof HIV-1 variants isolated from in vitro selection studies and frompatients treated with the protease inhibitor, nelfinavir [abstract 29]. In:Program and abstracts of the 5th Workshop on HIV Drug Resistance(Whistler, BC), 1996.

89. Patick AK, Duran M, Cao Y, et al. HIV-1 variants isolated from patientstreated with the protease inhibitor nelfinavir are not cross-resistant toother protease inhibitors. AIDS 1996;10:S18.

90. Hall CS, Raines CP, Barnett SH, Moore RD, Gallant JE. Efficacy of salvagetherapy containing ritonavir and saquinavir after failure of single pro-tease inhibitor–containing regimens. AIDS 1999;13:1207–12.

91. Molla A, Korneyeva M, Gao Q, et al. Ordered accumulation of mutationsin HIV protease confers resistance to ritonavir. Nat Med 1996;2:760–6.

92. Deeks SG, Hellmann NS, Grant RM, et al. Novel four-drug salvage treat-ment regimens after failure of a human immunodeficiency virus type 1protease inhibitor–containing regimen: antiviral activity and correlationof baseline phenotypic drug susceptibility with virologic outcome. J In-fect Dis 1999;179:1375–81.

93. Farthing C, Mess T, Ried C, Radhakrishna S, Wallace M. Ritonavir, sa-quinavir, and nevirapine as a salvage regiment for indinavir or ritonavirresistance [abstract 22356]. In: Program and abstracts of the 12th WorldAIDS Conference (Geneva). Geneva: Marathon Multimedia, 1998.

94. Stewart K, Park C, Nienaber V, et al. Molecular modeling and x-ray crystal-lographic studies of ritonavir, ABT-378, and their analogues bound toprotease [abstract 464]. In: Program and abstracts of the 4th Conferenceon Retroviruses and Opportunistic Infections (Washington, DC). Alex-andria, VA: Foundation for Retrovirology and Human Health, 1997.

95. Chen C, Niu P, Kati W, et al. Acitivity of ABT-378 against HIV protease–containing mutations conferring resistance to ritonavir [abstract 399].In: Program and abstracts of the 4th Conference on Retroviruses andOpportunistic Infections (Washington, DC). Alexandria, VA: Founda-tion for Retrovirology and Human Health, 1997.

96. Korneyeva M, Chernyvskiy T, Norbeck D, et al. Virological evaluation ofritonavir-resistant HIV to the HIV protease inhibitor ABT-378 [abstract447]. In: Program and abstracts of the 4th Conference on Retroviruses

and Opportunistic Infections (Washington, DC). Alexandria, VA: Foun-dation for Retrovirology and Human Health, 1997.

97. Kumar GN, Jayanti V, Johnson MK, Denissen JF. Increased bioavailabilityand plasma levels of the HIV-1 protease inhibitor ABT-378 in rats dueto inhibition of the in vivo metabolism by ritonavir [abstract 465]. In:Program and abstracts of the 4th Conference on Retroviruses and Op-portunistic Infections (Washington, DC). Alexandria, VA: Foundationfor Retrovirology and Human Health, 1997.

98. Lal R, Hsu A, Granneman GR, et al. Multiple dose safety, tolerability andpharmacokinetics of ABT-378 in combination with ritonavir [abstract647]. In: Program and abstracts of the 5th Conference on Retrovirusesand Opportunistic Infections (Chicago). Alexandria, VA: Foundationfor Retrovirology and Human Health, 1998.

99. Eron J, King M, Xu Y, et al. ABT-378/ritonavir (ABT-387/r) suppressesHIV RNA to !400 copies/mL in 95% of treatment-naive patients andin 78% of PI-experienced patients at 36 weeks [abstract LB20]. In: Pro-gram and abstracts of the 39th Interscience Conference on AntimicrobialAgents and Chemotherapy (San Francisco). Washington, DC: AmericanSociety for Microbiology, 1999.

100. Borin MT, Wang Y, Schneck DW, Li H, Brewer JE, Daenzer CL. Multiple-dose, safety, tolerance, and pharmacokinetics of the protease inhibitorPNU-140690 in healthy volunteers [abstract 648]. In: Program and ab-stracts of the 5th Conference on Retroviruses and Opportunistic Infec-tions (Chicago). Alexandria, VA: Foundation for Retrovirology and Hu-man Health, 1998.

101. Poppe SM, Slade DE, Chong KT, et al. Antiviral activity of the dihydro-pyrone PNU-140690, a new nonpeptidic human immunodeficiency virusprotease inhibitor. Antimicrob Agents Chemother 1997;41:1058–63.

102. Chong KT, Pagano PJ. In vitro combination of PNU-140690, a humanimmunodeficiency virus type 1 protease inhibitor, with ritonavir againstritonavir-sensitive and -resistant clinical isolates. Antimicrob AgentsChemother 1997;41:2367–73.

103. Gong Y, Robinson B, Rose R, et al. Resistance profile and drug combinationstudies of an HIV-1 protease inhibitor, BMS-232632 [abstract 603]. In:Program and abstracts of the 6th Conference on Retroviruses and Op-portunistic Infections (Chicago). Alexandria, VA: Foundation for Re-trovirology and Human Health, 1999.

104. O’Mara EM, Smith J, Olsen SJ, Tanner T, Schuster AE, Kaul S. BMS-232632:single and multiple oral dose safety and pharmacokinetic study in healthyvolunteers [abstract 604]. In: Program and abstracts of the 6th Conferenceon Retroviruses and Opportunistic Infections (Chicago). Alexandria, VA:Foundation for Retrovirology and Human Health, 1999.

105. Patick AK, Shintani M, Sato H, et al. Antiviral activity and resistance profileof AG1776, a novel inhibitor of HIV-1 protease [abstract 11]. In: Pro-gram and abstracts of the 6th Conference on Retroviruses and Oppor-tunistic Infections (Chicago). Alexandria, VA: Foundation for Retro-virology and Human Health, 1999.

106. Carr A, Samaras K, Burton S, et al. A syndrome of peripheral lipodystrophy,hyperlipidaemia and insulin resistance in patients receiving HIV proteaseinhibitors. AIDS 1998; 12:F51–8.

107. Viraben R, Aquilina C. Indinavir-associated lipodystrophy. AIDS 1998;12:F37–9.

108. Carr A, Samaras K, Chisholm DJ, Cooper DA. Pathogenesis of HIV-1protease inhibitor–associated peripheral lipodystrophy, hyperlipidaemia,and insulin resistance. Lancet 1998;351:1881–3.

109. Saint-Marc T, Partisani M, Poizot-Martin I, et al. A syndrome of peripheralfat wasting (lipodystrophy) in patients receiving long-term nucleosideanalogue therapy. AIDS 1999;13:1659–67.

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HIV-1 Protease Inhibitors

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