Deja Ch 2.2 Antiviral Flashcards
What enzyme adds the first phosphate to acyclovir?
Viral thymidine kinase
True or False? Monophosphorylated acyclovir is converted to the triphosphate form by viral enzymes.
False (host cell kinases are responsible for these reactions)
How does acyclovir triphosphate work as an antiviral agent?
Inhibits viral DNA replication by competing with deoxyguanosine triphosphate for viral DNA polymerase; incorporated into the viral DNA molecule and acts as a chain terminator
How does acyclovir triphosphate work as a chain terminator?
Lacks the ribosyl 3’ hydroxyl group
How do viruses become resistant to acyclovir?
Downregulation of viral thymidine kinase; lacking thymidine kinase altogether; altered specificity of viral thymidine kinase; altered specificity of viral DNA polymerase
Acyclovir is effective in treating which virus types?
Herpes simplex virus (HSV) 1 and 2; varicella-zoster virus (VZV). Acyclovir is 10 _ more potent against HSV than VZV
Is acyclovir effective in treating postherpetic neuralgia?
No (only effective against acute neuritis)
What is the oral bioavailability of acyclovir?
15%-30%. There is minimal systemic distribution after topical application.
What is the half-life of acyclovir in adults?
2.5-3 hours
Why is it necessary to maintain adequate hydration in patients receiving IV acyclovir therapy?
To prevent crystalluria or interstitial nephritis. Slow infusion additionally helps to avoid these adverse reactions.
What is the name of the prodrug that is converted to acyclovir and L-valine by first-pass metabolism?
Valacyclovir
What is the advantage of valacyclovir over acyclovir?
Higher oral bioavailability of 54%-70%
Famciclovir is a prodrug that is metabolized to what active metabolite?
Penciclovir
What is the bioavailability of penciclovir after oral administration of famciclovir?
70%
Is famciclovir effective in viral strains resistant to acyclovir secondary to mutated DNA polymerase?
Yes
Is famciclovir effective in viral strains resistant to acyclovir secondary to lack of thymidine kinase?
No
What is the mechanism of action of ganciclovir?
Phosphorylated to a substrate which competitively inhibits binding of deoxyguanosine triphosphate to DNA polymerase, thereby inhibiting viral DNA synthesis
Does ganciclovir have chain-terminating ability?
No
Ganciclovir is effective in treating which virus types?
HSV; VZV; human herpes virus (HHV)-6 and 8; cytomegalovirus (CMV). Activity against CMV is 100 _ greater than acyclovir. It may be used intraocularly for CMV retinitis.
What is the advantage of valganciclovir over its parent drug ganciclovir?
Valganciclovir (the valine ester) has up to 60% better oral availability than ganciclovir.
What is ganciclovir’s dose-limiting adverse effect?
Myelosuppression; thrombocytopenia; anemia; leukopenia
What are the adverse effects of ganciclovir?
Crystalluria; mucositis; rash; fever; hepatotoxicity; seizures; diarrhea; nausea; hematotoxicity
What is cidofovir used for?
CMV retinitis most commonly. It also has activity against HSV-1 and 2, varicella zoster virus (VZV), Epstein-Barr virus (EBV), HHV-6 and 8, adenovirus, poxviruses, polyomaviruses, and human papilloma virus (HPV).
What antiviral agent is a pyrophosphate analogue that acts as an inhibitor of viral RNA and DNA polymerase and HIV reverse transcriptase?
Foscarnet
Does foscarnet require activation by thymidine kinase?
No
Foscarnet is effective in treating which virus types?
Acyclovir-resistant HSV and VZV; ganciclovir-resistant CMV
Does foscarnet cause hematotoxicity?
Yes
What are the major adverse effects of foscarnet?
Hematotoxicity; fever; seizures; electrolyte abnormalities; nausea; vomiting; diarrhea
What types of electrolyte abnormalities can foscarnet cause?
Hyper- or hypocalcemia; hyper- or hypomagnesemia; hyper- or hypophosphatemia; hypokalemia
True of False? Amantadine is effective in treating both influenza A and B.
False (it is effective against the influenza A virus only)
What is the antiviral mechanism of action of amantadine?
Blocks the uncoating of influenza A virus, thereby preventing penetration of the virus into host cells
What other noninfectious disease processes is amantadine used for?
Parkinson disease; drug-induced extrapyramidal symptoms. It also increases dopamine levels in the synaptic cleft by either inhibiting reuptake into presynaptic neurons or by increasing release from presynaptic neurons. It may have anticholinergic effects.
What are the adverse effects of amantadine?
Seizures; insomnia; nervousness; livedo reticularis; orthostatic hypotension; peripheral edema; dry nose; xerostomia; nausea; anorexia
What is livedo reticularis?
A purplish discoloration of the skin caused by dilation of capillaries and venules secondary to stasis or changes in underlying blood vessels
Name two drugs that inhibit neuraminidase of both influenza A and B, thereby decreasing the likelihood of viral penetration into host cells:
Oseltamivir; zanamivir
Which neuraminidase inhibitor has an oral inhalational route of administration?
Zanamivir
Ribavirin is effective in treating which virus types?
Respiratory syncytial virus (RSV); influenza A and B; hepatitis C virus (HCV)
Ribavirin is used in conjunction with what other drug to treat HCV?
Interferon-alpha (IFN-_)
What are the adverse effects of ribavirin?
Anemia; neutropenia; thrombocytopenia; anorexia; headache; conjunctivitis; nausea; pharyngitis; lacrimation; alopecia; rash; flu-like syndrome; teratogenicity (pregnancy category X)
Name the major adverse effects of IFN-_:
Flu-like symptoms; depression; alopecia; insomnia; nausea
What is the name of the only available nucleotide reverse transcriptase inhibitor?
Tenofovir
Give examples of nucleoside reverse transcriptase inhibitors (NRTIs):
Zidovudine (AZT); stavudine (d4T); lamivudine (3TC); didanosine (ddl); abacavir (ABC); emtricitabine (FTC)
What adverse effect(s) are associated with all NRTIs?
Lactic acidosis with hepatic steatosis
What is the general mechanism of action of NRTIs?
Interference with HIV viral RNA-dependent DNA polymerase resulting in inhibition of HIV viral replication
What two NRTIs are thymidine analogs?
Zidovudine; stavudine
What NRTI is an adenosine analog?
Didanosine
What NRTI is a guanosine analog?
Abacavir
What two NRTIs are cytosine analogs?
- Emtricitabine 2. Lamivudine
Which NRTI should not be rechallenged if hypersensitivity is expected?
Abacavir (symptoms include fever, rash, nausea, vomiting, malaise, fatigue, and respiratory dysfunction)
Which NRTI can cause hyperuricemia?
Didanosine
Which two NRTIs can cause pancreatitis?
- Didanosine 2. Stavudine (dose-limiting effect)
Which two NRTIs can cause peripheral neuropathy?
- Didanosine 2. Stavudine (dose-limiting effect)
What is didanosine’s dose-limiting adverse effect?
Pancreatitis
What is stavudine’s dose-limiting adverse effect?
Peripheral neuropathy
What are the main adverse effects of AZT?
Anemia and neutropenia (dose-limiting effect/potentiated by vitamin B12); headache; nausea; insomnia; body aches; lactic acidosis
What is the dose-limiting adverse effect of AZT?
Hematotoxicity
What antiretroviral agent can cause Fanconi syndrome?
Tenofovir. Fanconi syndrome is impairment of the proximal tubule resulting in increased phosphate and calcium losses.
What NRTI can cause altered LFTs, lipoatrophy, hyperlipidemia, and ascending paresis?
Stavudine
Name three nonnucleoside reverse transcriptase inhibitors (NNRTIs):
- Delavirdine 2. Efavirenz 3. Nevirapine
What is the mechanism of action of efavirenz?
Binds directly to reverse transcriptase and blocks the RNA-and DNA-dependent DNA polymerase activity of reverse transcriptase
What is the class adverse effect(s) of the NNRTIs?
Rash
Which NNRTI can cause hepatitis and hepatic necrosis?
Nevirapine
Which NNRTI can cause abnormal dreams, impaired concentration, dizziness, and altered LFTs?
Efavirenz
Which NNRT can produce a false-positive urine test for Cannabis?
Efavirenz (in about 50% of patients)