Famciclovir

Antiviral, Systemic · Guanine analogue

Indications

Treatment of herpes zoster in immunocompetent and immunocompromised patients. Treatment of acute genital herpes infections and suppression of recurrent genital herpes infections in immunocompetent and immunocompromised patients.

Dosage

Shingles: Adults: 750 mg once daily at approximate the same time each day for 7 days, or 250 mg three times daily for 7 days. In immunocompromised patients, 500 mg three times daily for 10 days. Start treatment as soon as possible after onset of rash. Children: Not recommended. Genital herpes: Adults: First attack, 250 mg three times daily for 5 days started as soon as possible after onset of lesions. In immunocompromised, 500 mg twice daily for 7 days. Recurrent attack, 125 mg twice daily for 7 days, start treatment during prodromal period or as soon as possible after onset of lesions. Suppression: Adults: 250 mg twice daily. In HIV patients, 500 mg twice daily. Interrupt therapy at 6-12 mth intervals to reassess. Children: Not recommended.

Adverse Effects

Headache, nausea, dizziness, somnolence, GI upset, altered LFTs, rash, pruritus.

Risk Factor (Pregnancy/Lactation)

Pregnancy: No evidence of risk in humans. Lactation: Caution advised or effect undetermined. Contraindications: Complicated herpes zoster, immunocompromised patients with ocular herpes simplex or high risk of systemic involvement. Precautions: Renal impairment, severe hepatic impairment.

Interactions

Cimetidine, digoxin, probenecid, theophylline, raloxifene.

Advice to Patient

Take with or without meals. Contact prescriber if there is severe GI disturbances(such as nausea, vomiting, diarrhoea, constipation), muscle pain, headache, fatigue. Complete full course of therapy even if you feel better.

Pharmacokinetics

Absorption: Food reduces maximum peak penciclovir concentration and delays time to penciclovir peak; AUC remains the same. Metabolism: Rapidly deacetylated and oxidized to penciclovir (active prodrug). Bioavailability: Penciclovir: 77% ± 8%. Half-life elimination: Penciclovir: 2-4 hrs; Prolonged in renal impairment: CrCl 40-59 mL/min: Approx. 3.4 hrs. CrCl 20-39 mL/min: Approx. 6.2 hrs. CrCl <20 mL/min: Approx. 13.4 hrs. Intracellular penciclovir triphosphate: HSV 1: 10 hrs; HSV 2: 20 hrs; VZV: 7 hrs. Time to peak: Penciclovir: Approx. 1 hr. Excretion: Urine (73%). Faeces (27%).

Compiled by Healify Pharmacy from published drug references. How we compile it →

Always consult a pharmacist or doctor.