FAMCICLOVIR Drug Interactions: What You Need to Know

INTERACTIONS Probenecid: May increase penciclovir levels. Monitor for evidence of penciclovir toxicity. ( 7.2 )

7.1 Potential for Famciclovir Tablets to Affect Other Drugs The steady-state pharmacokinetics of digoxin were not altered by concomitant administration of multiple doses of famciclovir (500 mg three times daily). 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 coadministered with zidovudine or emtricitabine. An in vitro study using human liver microsomes suggests that famciclovir is not an inhibitor of CYP3A4 enzymes.

7.2 Potential for Other Drugs to Affect Penciclovir No clinically significant alterations in penciclovir pharmacokinetics were observed following single-dose administration of 500 mg famciclovir after pretreatment with multiple doses of allopurinol, cimetidine, theophylline, zidovudine, promethazine, when given shortly after an antacid (magnesium and aluminum hydroxide), or concomitantly with emtricitabine. No clinically significant effect on penciclovir pharmacokinetics was observed following multiple-dose (three times daily) administration of famciclovir (500 mg) with multiple doses of digoxin. Concurrent use with probenecid or other drugs significantly eliminated by active renal tubular secretion may result in increased plasma concentrations of penciclovir. The conversion of 6-deoxy penciclovir to penciclovir is catalyzed by aldehyde oxidase. Interactions with other drugs metabolized by this enzyme and/or inhibiting this enzyme could potentially occur. 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 penciclovir and raloxifene has not been conducted.

Famciclovir tablets are contraindicated in patients with known hypersensitivity to the product, its components, or Denavir ® (penciclovir cream). Known hypersensitivity to the product, its components, or Denavir ® (penciclovir cream). ( 4 )

AND PRECAUTIONS Acute renal failure: May occur in patients with underlying renal disease who receive higher than recommended doses of famciclovir for their level of renal function. Reduce dosage in patients with renal impairment. ( 2.3 , 8.6 )

5.1 Acute renal failure Cases of acute renal failure have been reported in patients with underlying renal disease who have received inappropriately high doses of famciclovir tablets for their level of renal function. Dosage reduction is recommended when administering famciclovir tablets to patients with renal impairment <span class="opacity-50 text-xs">[see Dosage and Administration ( 2.3 ), Use in Specific Populations ( 8.6 )]</span>.