Anti-viral Agents (complete) Flashcards
What are the different classifications of anti-viral agents for flu?
1) Inhibition of viral neuraminidase
2) Inhibition of uncoating
What are the different classifications of anti-viral agents for herpes?
1) Inhibition of viral genome replication (viral DNA polymerase)
2) Inhibitors of viral penetration
What are the different classifications of anti-viral agents for RSV?
Only one type
1) Purine nucleoside analogy
What are the different classifications of anti-viral agents for cytomegalovirus?
1) Inhibition of viral DNA polymerase
2) Ganciclovir/Valganciclovir
3) Foscarnet
What are the two anti-virals for flu that are neuraminidase inhibitors?
1) Oseltamivir
2) Zanamivir
Describe the mechanism of action for neuraminidase inhibitors of flu
- Works against influenza A and B
- If NA activity is blocked virions clump at cell surface => decrease viral infectivity
- NA inhibition impairs viral penetration through mucin secretions => decreased infection of other respiratory epithelial cells
Describe flu’s resistance to NA inhibitors
- It’s rare
- If it does happen, through mutations in neuraminidase or hemagluttinin
How is oseltamivir absorbed?
PO
- a prodrug
- 80% bioavailability
How is zanamivir absorbed?
Via inhalation
Goal: to deliver to respiratory tract
How is oseltamivir eliminated?
- kidneys (glomer filtration-tubular secretion)
- Dosage must be changed if pt has renal probs
How is zanamivir eliminated?
- 10-20% of inhaled dose is absorbed
- Remainder excreted via urine
Describe the clinical use of oseltamivir
Who: Children (>1yo) and adults) When: Start w/in 48hrs of symptoms Purpose: decreases severity and duration of flu
Can be given prophylactically => 70-90% effective in prevention
Describe the clinical use of zanamivir
Who: Those >7yo When: Start w/in 2 days of symptoms Purpose: Shorten duration -- decrease lower respiratory tract complications
What are the adverse rxns associated with oseltamivir?
- Nausea and vomiting
- Abdominal pain
Decreased if taken w/food
What are the adverse rxns associated with zanamivir?
Cough, brochospasm
CAN BE SEVERE
What are the two anti-virals for flu that inhibit uncoating?
1) Amantadine
2) Rimantadine
Describe the mechanism of action for uncoating inhibitors for flu
- Blocks virally-encoded H+ ion channel —AKA: M2 protein
- Prevents the pH change necessary for uncoating!
Describe flu’s resistance to uncoating inhibitors
- Mutations in transmembrane domains of M2 proton channel
- Can no longer block that channel
How are amantadine/rimantadine absorbed?
effective PO
ACCUMULATES in LUNGS
How is amantadine excreted?
Unchanged in urine
How is rimantadine excreted? Discuss the limits of its distribution
- Hepatic elimination
- Increased protein-bind limits distribution to CNS
Describe the clinical uses of amantadine and rimantadine. Why is use currently limited?
- Used for prophylaxis and tx of influenza A
- Limited use: b/c of RESISTANCE
What are the adverse rxns associated with amantadine?
- Insomnia
- Concentration difficulty
- Lightheadedness/dizziness
- Headache
- GI upset
What are the adverse rxns associated with rimantadine?
Better than amantadine but similar effects
CNS probs not as bad b/c of decreased CNS penetration
- Insomnia
- Concentration difficulty
- Lightheadedness/dizziness
- Headache
- GI upset
Describe the mechanism of action of acyclovir and its analogs
- Diffuse into cell => triphosphorylated by intracellular kinases
- The Acyclo triphosphate inhibits viral DNA polymerase (more sensitive than human DNA poly)
- A DNA chain terminator w/ irreversible binding btwn DNA poly and terminated chain
Describe the selectively toxic effects of acyclovir in herpes tx
- 1st phosphorylation step by herpes-encoded thymidine kinase
- Only occurs in infected cells
Describe viral resistance to acyclovir and its analogs
MOST COMMON:
- Reudction/loss of expression of viral thymidine kinase
Also:
- altered TK substrate specificity
- altered affinity of viral DNA poly activity
Resistance happens mainly in immunosuppressed pts receiving extended acyclovir tx regimens