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ANTIVIRAL DRUGS
Understanding Viruses
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
Understanding Viruses
Viruses are difficult to kill because they live inside the cells
Any drug that kills a virus may also kill cells
Viral Infections
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 pharmacologic therapy AIDS patients, disease attacks immune system
Antivirals
Viruses controlled by current antiviral therapy
Cytomegalovirus (CMV) Hepatitis viruses Herpes viruses Human immunodeficiency virus (HIV) Influenza viruses (the “flu”) Respiratory syncytial virus (RSV)
Antivirals
Key characteristics of antiviral drugs
Able to enter the cells infected with virus
Interfere with viral nucleic acid synthesis and/or regulation
Some drugs interfere with ability of virus to bind to cells
Some drugs stimulate the body’s immune system
Best responses to antiviral drugs are in patients with competent immune systems
A healthy immune system works synergistically with the drug to eliminate or suppress viral activity
Antivirals
Opportunistic infections
Occur in immunocompromised patients
Infections that would not normally harm an immunocompetent person
Require long-term prophylaxis and anti-infective drug therapy
Can be other viruses, fungi, bacteria, or protozoa
Antiviral Medications
Antiviral drugs Used to treat infections caused by viruses other
than HIV Antiretroviral drugs
Used to treat infections caused by HIV, the virus that causes AIDS
Herpes-Simplex Viruses HSV-1 (oral herpes) HSV-2 (genital herpes)
Varicella Zoster Virus Chickenpox Shingles
Antiviral Drugs: Nonretroviral Mechanism of action
Inhibit viral replication Used to treat non-HIV viral
infections Influenza viruses HSV (herpes simplex virus), VZV (vericella zoster
virus) CMV (cytomegalovirus) Hepatitis A, B, C (HAV, HBV, NCV)
Adverse Effects Vary with each drug Healthy cells are often killed also, resulting in
serious toxicities
Antivirals Drugs-NonretroviralAmantadine (Symmetrel)
Narrow antiviral spectrumactive only against influenza A
Used prophylactically when vaccine is not available or cannot be given
Therapeutic use can reduce recovery time
CNS effects: insomnia, nervousness, lightheadedness
GI effects: anorexia, nausea, others
Antivirals Drugs-NonretroviralRimantadine (Flumadine)
Same spectrum of activity, mechanism of action, and indications as amantadine
Fewer CNS adverse effects
Causes GI upset
Antivirals Drugs-NonretroviralAcyclovir (Zovirax)
Synthetic nucleoside analog
Used to suppress replication of: HSV-1(oral herpes), HSV-2(genital herpes), VZV (Varicella – chickenpox or shingles)
Drug of choice for treatment of initial and recurrent episodes of these infections
Oral, topical, parenteral forms
Antivirals Drugs-NonretroviralGanciclovir (Cytovene)
Synthetic nucleoside analog
Used to treat infection with cytomegalovirus (CMV)
Oral, parenteral forms
CMV retinitis Ophthalmic form surgically implanted Ocular injection (fomivirsen)
Antivirals Drugs-NonretroviralDose-Limiting Toxicities
ganciclovir and zidovudine Bone marrow toxicity
foscarnet and cidofovir Renal toxicity
Antivirals Drugs-NonretroviralNeuraminidase Inhibitors
oseltamivir (Tamiflu) and zanamivir (Relenza) Active against influenza types A & B
Use: Reduce duration of illness
oseltamivir: causes nausea & vomiting
zanamivir: causes diarrhea, nausea, sinusitis
Treatment should begin within 2 days of influenza symptom onset
Antivirals Drugs-NonretroviralRibavirin
Synthetic nucleoside analog
Given orally, or oral or nasal inhalation
Inhalation form (Virazole) used for hospitalized infants with RSV (respiratory syncytialvirus) infections
HIV
Human immunodeficiency virus infection ELISA (enzyme-linked immunosorbent assay)
Detects HIV exposure based on presence of human antibodies to the virus in the blood
Retrovirus Transmitted by:
Sexual activity, intravenous drug use, perinatally from mother to child
Five Stages of HIV Infection
Stage 1: asymptomatic infection Stage 2: early, general symptoms of disease Stage 3: moderate symptoms Stage 4: severe symptoms, often leading to death
WHO model stages
Opportunistic Infections
Protozoal Toxoplasmosis of the brain, others
Fungal Candidiasis of the lungs, esophagus, trachea Pneumocystis jiroveci pneumonia, others
Viral CMV disease, HSV infection, others
Bacterial Various mycobacterial infections, others Extrapulmonary TB
Opportunistic neoplasias Kaposi’s sarcoma, others
Antiretroviral Drugs
HAART - Highly active antiretroviral therapy
Includes at least three medications “cocktails”
These medications work in different ways to reduce the viral load
Antiretroviral Drugs
Reverse transcriptase inhibitors (RTIs) Block activity of the enzyme reverse transcriptase,
preventing production of new viral DNA Reverse transcriptase inhibitors (RTIs)
Nucleoside RTIs (NRTIs) Nonnucleoside RTIs (NNRTIs) Nucleotide RTIs (NTRTIs)
Examplesabacavir (Ziagen) delavirdine (Rescriptor)didanosine (Videx) lamivudine (Epivir)stavudine (Zerit) tenofovir (Viread)
Antiretroviral Drugs
Protease inhibitors (PIs) Inhibit the protease retroviral enzyme,
preventing viral replication Examples: amprenavir (Agenerase) indinavir
(Crixivan) nelfinavir (Viracept) ritonavir (Norvir) saquinavir (Invirase)
Antiretroviral Drugs
Fusion inhibitors
Inhibit viral fusion, preventing viral replication
Newest class of antiretroviral drugs
Example: enfuvirtide (Fuzeon)
Antiretroviral Drugs
Combinations of multiple antiretroviral medications are common
Adverse effects vary with each drug and may be severemonitor for dose-limiting toxicities
Monitor for signs of opportunistic diseases
Antiretroviral Drugs:Adverse Effects
Numerous and vary with each drug
Drug therapy may need to be modified because of adverse effects
Goal is to find the regimen that will best control the
infection with a tolerable adverse effect profile
Medication regimens change during the course of the illness
Nursing Implications
Before therapy, assess underlying disease, history, allergies
Assess baseline VS and nutritional status
Assess for contraindications, conditions that may indicate cautious use, and potential drug interactions
Nursing ImplicationsPatient Education
Consult their physician before taking other medication, including OTCs
Good hygiene
Antiviral drugs are not cures but help manage symptoms
Take these medications exactly as prescribed
Take medications for the full course of treatment
Nursing ImplicationsPatient Education
Teach each proper application for ointments, aerosol powders
Hand washing before and after administration of medications
Wear glove or finger cot when applying ointments
Start therapy with antiviral drugs at the earliest sign of recurrent episodes of genital herpes or herpes zoster
Nursing Implications
Monitor for therapeutic effects Effects will vary depending on the type of
viral infection Effects range from delayed progression of
AIDS and other viruses to decrease in flu-like symptoms, decrease in frequency of herpes-like flare-ups, or crusting over of herpetic lesions
Monitor for adverse effects Effects are varied and specific to each drug