Famciclovir rapidly undergoes biotransformation to penciclovir, which has inhibitory activity against HSV types 1 (HSV-1) and 2 (HSV-2), varicella-zoster virus (VZV). Thymidine kinase then phosphorylates penciclovir to a monophosphate form, which is then converted to penciclovir triphosphate. This inhibits HSV-2 DNA polymerase by competing with deoxyguanosine triphosphate, thus inhibiting herpes viral DNA synthesis and replication.

Herpes zoster (shingles), Recurrent herpes labialis, Genital herpes, Acute treatment of recurrent mucocutaneous herpes in HIV-infected patients, Acute treatment of recurrent episodes of genital herpes, Suppression of recurrent episodes of genital herpes

Oral (Adult)-

Herpes zoster (shingles): 500 mg tid for 7 days. Immunocompromised patients: 500 mg tid for 10 days.

Haemodialysis patients: 250 mg after each dialysis run during 7 days. Immunocompromised patients: Same dose but treatment is given for 10 days.

• CrCl (mL/min) <20: 250 mg once daily for 7 days.
• CrCl (mL/min) 20-39: 500 mg once daily for 7 days.
• CrCl (mL/min) 40-59: 500 mg bid for 7 days.

Recurrent herpes labialis: 1.5 g as a single dose.

Haemodialysis patients: 250 mg after dialysis run.

• CrCl (mL/min) <20: 250 mg as a single dose.
• CrCl (mL/min) 20-39: 500 mg as a single dose.
• CrCl (mL/min) 40-59: 750 mg as a single dose.

Genital herpes: 1st episode: 250 mg tid for 5 days. Immunocompromised patients: 500 mg bid for 7 days.

Haemodialysis patients: 250 mg after each dialysis run during 5 days.

• CrCl (mL/min) <20: 250 mg once daily for 5 days.
• CrCl (mL/min) 20-39: 250 mg bid for 5 days.

Acute treatment of recurrent mucocutaneous herpes in HIV-infected patients: 500 mg bid for 7 days.

Haemodialysis patients: 250 mg after each dialysis run during 7 days.

• CrCl (mL/min) <20: 250 mg once daily for 7 days.
• CrCl (mL/min) 20-39: 500 mg once daily for 7 days.

Acute treatment of recurrent episodes of genital herpes: 125 mg bid for 5 days or 1 g bid for 1 day. Immunocompromised patients: 500 mg bid for 7 days.

Haemodialysis patients: 125 mg after each dialysis run during 5 days. Haemodialysis patients (immunocompromised): 250 mg after each dialysis run during 7 days.

• CrCl (mL/min) <20: 125 mg once daily for 5 days.
• CrCl (mL/min) ≥20: 125 mg bid for 5 days.
• CrCl (mL/min) <20: Immunocompromised: 250 mg once daily for 7 days.
• CrCl (mL/min) 20-39: Immunocompromised: 500 mg once daily for 7 days.

Suppression of recurrent episodes of genital herpes: 250 mg bid. Immunocompromised patients: 500 mg bid. Suppressive treatment is interrupted every 6-12 mth for observation.

Haemodialysis patients: 125 mg after each dialysis run. Haemodialysis patients (immunocompromised): 250 mg after each dialysis run.

• CrCl (mL/min) 20: 125 mg once daily. Immunocompromised: 250 mg once daily.
• CrCl (mL/min) 20-39: 125 mg bid. Immunocompromised: 500 mg once daily.

Hypersensitivity to famciclovir and penciclovir.

Headache, nausea, diarrhoea, fatigue, dizziness, fever, paraesthesia, somnolence, vomiting, constipation, anorexia, abdominal pain, flatulence, dyspepsia; increased serum levels of ALT, alkaline phosphatase, total bilirubin and albumin; pruritus, pharyngitis, sinusitis, injury, generalised pain, rigors, back pain, arthralgia; increased serum phosphate, Na and K levels; abnormal leukocyte counts, purpura, angioedema.

Renal impairment. Pregnancy and lactation.

Overdose Effects

Acute renal failure in patients with renal disease. Management: Supportive and symptomatic treatment. May be removed by haemodialysis.

Pregnancy & Lactation

Category B: Either animal-reproduction studies have not demonstrated a foetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the 1st trimester (and there is no evidence of a risk in later trimesters).