Effects on P enciclovir
No clinically significant alterations in penciclovir pharmacokinetics were observed following single-dose administration of 500-mg famciclovir after pre-treatment with multiple doses of allopurinol, cimetidine, theophylline, zidovudine, or promethazine, when given shortly after an antacid (magnesium and aluminium hydroxide), or concomitantly with emtricitabine. No clinically significant effect on penciclovir pharmacokinetics was observed following multiple-dose (t.i.d.) administration of famciclovir (500 mg) with multiple doses of digoxin.
Clinical interaction studies of famciclovir with cimetidine and promethazine, in vitro inhibitors of aldehyde oxidase, did not show relevant effects on the formation of penciclovir. Raloxifene, a potent aldehyde oxidase inhibitor in vitro, could decrease the formation of penciclovir. However, a clinical drug-drug interaction study to determine the magnitude of interaction between pencyclovir and raloxifene has not been conducted.
Effects of F amciclovir on Co-administered D rugs
The steady-state pharmacokinetics of digoxin were not altered by concomitant administration of multiple doses of famciclovir (500 mg t.i.d.). No clinically significant effect on the pharmacokinetics of zidovudine, its metabolite zidovudine glucuronide or emtricitabine was observed following a single oral dose of 500-mg famciclovir co-administered with zidovudine or emtricitabine.
An in vitro study using human liver microsomes suggests that famciclovir is not an inhibitor of CYP4503A4 enzymes.