Systemic Antivirals

shevyatiwari's version from 2015-10-17 06:48


Question Answer
A guanosine analogT
Activation requires phosphorylation by viral thymidine kinaseT
Activation requires bi and triphosphorylation by host cellular enzymesT
Biphosphorylated ACV inhibits viral DNA polymerase by serving as an obligate chain terminatorF, triphosphorylated.
ACV causes reversible inhibition of viral DNA synthesisF, irreversible
ACV causes greater inactivation of the cellular DNA polymerase cf viral polymeraseF
BA of 50%F, 15-30%
Peak levels in 1.5-2 hoursT
Half life of 2 hoursF, 1.3-1.5 hours
Metabolised in the liverT but no hepatic microsomal metabolism therefore few drug interactions.
Excreted in the urineF, urine and faeces equally
Cat AF, B
IV ACV has greater BA than PO ACVT
HSV2 resistance is greater in the HIV populationT
IV acyclovir is safe for pregnant women with pneumoniaT
GI S/E most commonT, generally well tolerated
Reversible renal impairment can occur du to crystalline nephropathyT
Probenicid -> delayed renal clearanceT
Zidovudine -> increased drowsiness and lethargyT
Is a prodrugF
Resistance is due to mutations in viral TKT, also due to mutations in viral DNA polymerase


Question Answer
Is the metabolite of ACVF, the prodrug. it is the 1 valyl ester of acyclovir with bioavailability 3-5 times greater than acyclovir
BA is 2 times greater than ACVF, 3-5 times (equivalent to IV ACV)
BA of approx 55%T
Half life of 2.5-3.3 hoursT
About 20% protein boundT
Less protein bound than ACVT. 13.5-17.9 vs 9-33% for acyclovir
Metabolised in the liverT. Hepatic metabolism but NO CYP metabolism therefore few drug interactions. Excretion 50:50 urine ;faeces like acyclovir and unlike famcic 73:23
Excreted in hepatobiliaryF, equal urine and faeces
Cat BT
Cimetidine -> decreased conversion to acyclovirF, decreases rate but not extent of conversion
Probenicid -> Decreased renal excretionF. Probenecid and cimetidine decreases rate but not conversion of val-acaylovir.
Probenecid targets both acyclovir and famciclovir to increase bioavailability via decreased renal clearance and renal tubular secretion.
Has no advantages over ACV apart from dosing frequency in VZVF, reduces PHN
Recurrent EM may be treated with ACVT (due to aetiology of HSV)


Question Answer
Is the prodrug of ganciclovirF, of penciclovir
A guanine analogueF, an acyclic nucleoside
Requires phosphorylation to become activeT
Once phosphorylated, is equivalent to phosphorylated ACVF, longer half life in HSV infected cells (10-20 hours in HSV, 7 hours in VZV cf < 1 hour)
BA of 50%F, 77%
Better BA than either ACV, VACVT
Cat BT
Is equivalent to ACV in HZF, equivalent to VACV
Probenicid -> decreased renal excretionT increases bioavailability by decreasing renal clearance due to decreased renal tubular secretion,
Cimetidine -> increase in penciclovirT
Theophylline -> decreased clearance of penciclovirT, however not clinically significant
ACV resistant HSV strains are often amenable to famciclovirF, often resistant to famciclovir and valaciclovir
Interacts with digoxinT digoxin levels increased by 19%


Question Answer
VZV is a live vaccineT
Given at 1 year and 4-6 yearsT
HZ is less common if VZV vaccine givenT
Decreases incidence of VZV by 50%T

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