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Nelia B. Perez RN, MSNPCU-MJCN
BSN 2014
Obligate intracellular parasites Consist of a core genome in a protein
shell and some are surrounded by a lipoprotein
lack a cell wall and cell membrane do not carry out metabolic processes Replication depends on the host cell
machinery
Steps for Viral Replication 1) adsorption and penetration into cell 2) uncoating of viral nucleic acid 3) synthesis of regulatory proteins 4) synthesis of RNA or DNA 5) synthesis of structural proteins 6) assembly of viral particles 7) release from host cell
Block viral entry into the cell or must work inside the cell
Most agents are pyrimidine or purine nucleoside analogs
Acyclovir- prototype Valacyclovir Famciclovir Penciclovir Trifluridine Vidarabine
an acyclic guanosine derivative Phosphorylated by viral thymidine
kinase Di-and tri-phosphorylated by host
cellular enzymes Inhibits viral DNA synthesis by:
1) competing with dGTP for viral DNA polymerase
2) chain termination
Alteration in viral thymidine kinase
Alteration in viral DNA polymerase
Cross-resistance with valacyclovir, famciclovir, and ganciclovir
Oral, IV, and Topical formulations Cleared by glomerular filtration and
tubular secretion Uses:
Herpes Simplex Virus 1 and 2 (HSV) Varicella-zoster virus (VZV)
Side Effects: nausea, diarrhea, headache, tremors, and delirium
L-valyl ester of acyclovir Converted to acyclovir when ingested M.O.A.: same as acyclovir Uses:
1) recurrent genital herpes 2) herpes zoster infections
Side Effects: nausea, diarrhea, and headache
Prodrug of penciclovir (a guanosine analog)
M.O.A.: same as acyclovir does not cause chain termination Uses: HSV-1, HSV-2, VZV, EBV, and
hepatitis B Side Effects: nausea, diarrhea, and
headache
Trifluridine- fluorinated pyrimidine inhibits viral DNA synthesis same as
acyclovir incorporates into viral and cellular DNA Uses: HSV-1 and HSV-2 (topically)
An adenosine analog inhibits viral DNA polymerase incorporated into viral and cellular DNA metabolized to hypoxanthine
arabinoside Side Effects: GI intolerance and
myelosuppression
Gancyclovir Valgancyclovir Cidofovir Foscarnet Fomivirsen
An acyclic guanosine analog requires triphosphorylation for activation monophosphorylation is catalyzed by a
phosphotransferase in CMV and by thymidine kinase in HSV cells
M.O.A.: same as acyclovir Uses: CMV*, HSV, VZV,and EBV Side Effect: myelosuppression
Monovalyl ester prodrug of gancyclovir Metabolized by intestinal and hepatic
esterases when administered orally
M.O.A.: same as gancyclovir Uses: CMV* Side Effect: myelosuppression
Aphosphorylation cytosine analog not dependent on viral enzymes Uses: CMV*, HSV-1, HSV-2, VZV, EBV,
HHV-6, adenovirus, and human papillomavirus
Side Effects: nephrotoxicity (prevented by admin. of probenecid)
Resistance: mutation in DNA polymerase gene
An inorganic pyrophosphate inhibits viral DNA polymerase, RNA
polymerase, and HIV reverse transcriptase does not have to be phosphorylated Uses: HSV, VZV, CMV, EBV, HHV-6, HBV, and
HIV Resistance due to mutations in DNA
polymerase gene Side Effects: hypo- or hypercalcemia and
phosphotemia
An oligonucleotide M.O.A.: binds to mRNA and inhibits
protein synthesis and viral replication Uses: CMV retinitis Side effects: iritis and increased
intraocular pressure
1) Nucleoside Reverse Transcriptase Inhibitors (NRTIs)
2) Nonnucleoside Reverse Transcriptase Inhibitors (NNRTIs)
3)Protease inhibitors
Zidovudine (AZT) Didanosine- causes pancreatitis* Lamivudine- causes pancreatitis Zalcitabine- causes peripheral neuropathy*
Stavudine- causes peripheral neuropathy* Abacavir
A deoxythymidine analog enters the cell via passive diffusion must be converted to the triphosphate
form by mammalian thymidine kinase competitively inhibits deoxythymidine
triphosphate for the reverse transcriptase enzyme
causes chain termination
Due to mutations in the reverse transcriptase gene
more frequent after prolong therapy and in persons with HIV
Available in IV and oral formulations activity against HIV-1, HIV-2, and
human T cell lymphotropic viruses mainly used for treatment of HIV,
decreases rate of progression and prolongs survival
prevents mother to newborn transmission of HIV
Myelosuppression, including anemia and neutropenia
GI intolerance, headaches, and insomnia
Didanosine- synthetic deoxy-adenosine analog; causes pancreatitis*
Lamivudine- cytosine analog Zalcitabine- cytosine analog; causes
peripheral neuropathy* Stavudine- thymidine analog;causes
peripheral neuropathy* Abacavir- guanosine analog; more
effective than the other agents; fatal hypersensitivity reactions can occur
Tenofovir Adefovir
An acyclic nucleoside phosphonate analog of adenosine
M.O.A.- competively inhibits HIV reverse transcriptase and causes chain termination after incorporation into DNA
Uses – in combination with other antiretrovirals for HIV-1 suppression
An analog of adenosine monophosphate Phosphorylated by cellular kinases M.O.A. - Competitively inhibits HBV
DNA polymerase and results in chain termination after incorporation into viral DNA
Uses - Hepatitis B Side effects - nephrotoxicity
Nevirapine Delavirdine Efavirenz
Bind to site on viral reverse transcriptase, different from NRTIs
results in blockade of RNA and DNA dependent DNA polymerase activity
do not compete with nucleoside triphosphates
do not require phosphorylation these drugs can not be given alone substrates and inhibitors of CYP3A4
Nonnucleoside Reverse Transcriptase Inhibitors (NNRTIs)
Nevirapine- prevents transmission of HIV from mother to newborn when given at onset of labor and to the neonate at delivery
Delavirdine- teratogenic, therefore can not be given during pregnancy
Efavirenz- teratogenic, therefore can not be given during pregnancy
Indinavir Ritonavir Saquinavir Nelfinavir Amprenavir
The protease enzyme cleaves precursor molecules to produce mature, infectious virions
these agents inhibit protease and prevent the spread of infection
These agents cause a syndrome of altered body fat distribution, insulin resistance, and hyperlipidemia
M.O.A.: Specific inhibitors of the HIV-1 protease enzyme
M.O.R.: mediated by expression of multiple and variable protease amino acid substitutions
Side Effects:hyperbilirubinemia Contraindications:inhibitor/substrate for
CPY3A4, do not give with antifungal azoles
A synthetic peptide-like substrate analog
inhibits HIV-1 protease
prevents cleavage of viral polyproteins
M.O.A.: Specific inhibitors of the HIV-1 protease enzyme
M.O.R.: mediated by expression of multiple and variable protease amino acid substitutions
Less cross-resistance with Amprenavir Side Effects: diarrhea and flatulence Amprenavir can cause Stevens-Johnson
syndrome Contraindications:inhibitor/substrate for
CPY3A4
Enfuvirtide (T-20)- binds to the gp41 subunit of the viral envelope glycoprotein, preventing the conformational changes required for fusion of the viral and cellular membranes
By blocking fusion (entry into cell), FUZEON prevents HIV from infecting CD4 cells
from Fuzeon.com
Lamivudine -Nucleoside Reverse Transcriptase Inhibitor (NRTI)
Adefovir -Nucleotide Inhibitor Interferon Alfa Pegylated Interferon Alfa Ribavirin
Interferon Alfa
Endogenous proteins
induce host cell enzymes that inhibit viral RNA translation and cause degradation of viral mRNA and tRNA
Bind to membrane receptors on cell surface May also inhibit viral penetration, uncoating,
mRNA synthesis, and translation, and virion assembly and release
Pegylated interferon Alfa A linear or branced polyethylene
gylcol (PEG) moiety is attached to covalently to interferon
Increased half-life and steady drug concentrations
Less frequent dosing Tx chronic hepatitis C in combination
with ribavirin
A guanosine analog phosphorylated intracellularly by host
enzymes inhibits capping of viral messenger RNA inhibits the viral RNA-dependent RNA
polymerase inhibits replication of DNA and RNA
viruses
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Amantadine Rimantadine Zanamivir
cyclic amines inhibit the uncoating of viral RNA
therefore inhibiting replication resistance due to mutations in the
RNA sequence coding for the structural M2 protein
used in the prevention and treatment of Influenza A
Inhibits the enzyme neuraminidase inhibit the replication of influenza A
and Influenza B treats uncomplicated influenza
infections administered intranasally
Viral Replication A virus cannot replicate on its own. It must attach to and enter a host cell. It then uses the host cell’s energy to synthesize
protein, DNA, and RNA.
Viruses are difficult to kill because they liveinside our cells.
Any drug that kills a virus may also kill our cells.
Competent immune system: Best response to viral infections
A well-functioning immune system will eliminate or effectively destroy virus replication
Immunocompromised patients have frequent viral infections
Cancer patients, especially leukemia or lymphoma
Transplant patients, due to pharmacological therapy
AIDS patients, disease attacks immune system
Key characteristics of antiviral drugs: Able to enter the cells infected with virus.
Interfere with viral nucleic acid synthesis and/or regulation.
Some agents interfere with ability of virus to bind to cells.
Some agents stimulate the body’s immune system.
Viruses killed by current antiviral therapy:
cytomegalovirus (CMV) herpes simplex virus (HSV) human immunodeficiency virus (HIV) influenza A (the “flu”)
respiratory syncytial virus (RSV)
Inhibit viral replication Inhibit viral attachment Prevent genetic copying of virus Prevent viral protein production
Two types of nucleosides:Purine nucleosides guanine adenosine
Pyrimidine nucleosides thymine cytosine
Agent Antiviral Activityguanines
acyclovir HSV 1 & 2, VZV
ganciclovir (DHPG) CMV retinitis and systemic CMV infection
ribavirin (RTCD) Influenza types A and B, RSV, LV, HV
adenosines
didanosine (ddl) HIV
vidarabine (Ara-A) HSV, herpes zoster
Agent Antiviral Activitycytosines
lamivudine (3TC) HIVzalcitabine (ddC) HIV
thymineidoxuridine (IDU) HSVstavudine (d4T) HIVtrifluridine HSVzidovudine (AZT) HIV
amantadine (Symmetrel) and rimantadine (Flumadine)
influenza A
foscarnet (Foscavir) CMV (retinitis and systemic)
Neuraminidase Inhibitors: oseltamivir (Tamiflu) and zanamivir (Relenza)
influenza types A and B
acyclovir Burning when topically applied, nausea,
vomiting, diarrhea, headache
amantadine and rimantadine Anticholinergic effects, insomnia,
lightheadedness, anorexia, nausea
didanosine (ddl) Pancreatitis, peripheral neuropathies, seizures
zidovudine (AZT) Bone marrow suppression, nausea, headache
foscarnet (Foscavir) Headache, seizures, acute renal failure,
nausea, vomiting, diarrhea
ganciclovir (Cytovene) Bone marrow toxicity, nausea, anorexia,
vomiting
Before beginning therapy, thoroughly assess underlying disease and medical history, including allergies.
Assess baseline VS and nutritional status. Assess for contraindications, conditions
that may indicate cautious use, and potential drug interactions.
Be sure to teach proper application technique for ointments, aerosol powders, etc.
Emphasize hand washing before and after administration of medications to prevent site contamination and spread of infection.
Patients should wear a glove or finger cot when applying ointments or solutions to affected areas.
Instruct patients to consult their physician before taking any other medication, including OTC medications.
Emphasize the importance of good hygiene.
Inform patients that antiviral agents are not cures, but do help to manage symptoms.
Instruct patients on the importance of taking these medications exactly as prescribed and for the full course of treatment.
With zidovudine: Inform patients that hair loss MAY occur so
that they are prepared for this rare adverse reaction.
This medication should be taken on an empty stomach.
Monitor for side effects: effects are varied and specific to each agent
Monitor for therapeutic effects: effects will vary depending on the type of viral
infection Effects range from delayed progression of AIDS
and ARC to decrease in flu-like symptoms, decreased frequency of herpes-like flare-ups, or crusting over of herpetic lesions.
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