famciclovir
Famvir

Available forms
Available by prescription only
Tablets: 125 mg, 250 mg, 500 mg

Indications and dosages
 Management of acute herpes zoster in immunocompetent patients. Adults: 500 mg P.O. q 8 hours for 7 days.
≡ Dosage adjustment. For adults with reduced renal function, adjust dosage as below.

Creatinine clearance (ml/min) Dosage regimen 40-59 500 mg q 12 hr 20-39 500 mg q 24 hr < 20 250 mg q 48 hr

 Recurrent genital herpes in immunocompetent patients. Adults: 125 mg P.O. b.i.d. for 5 days.
 Chronic suppressive therapy for recurrent episodes of genital herpes in immunocompetent patients. Adults: 250 mg P.O. q 12 hours for up to 1 year.
≡ Dosage adjustment. For adults with reduced renal function, adjust dosage as below.

Creatinine clearance (ml/min) Dosage regimen 40-59 125 mg q 12 hr 20-39 125 mg q 24 hr < 20 125 mg q 48 hr

 Chronic suppression or maintenance prophylaxis of HSV infection in HIV-infected patients. Adults: 500 mg P.O. b.i.d. for 7 days.

Pharmacodynamics
Antiviral action: Famciclovir, a prodrug, changes to an active antiviral compound, penciclovir. It enters viral cells (herpes simplex types 1 and 2, varicella zoster), where it inhibits DNA polymerase, viral DNA synthesis, and, thus, viral replication.

Pharmacokinetics
Absorption: Absolute bioavailability of famciclovir is 77%. Bioavailability isn’t affected by food.
Distribution: Less than 20% protein-bound.
Metabolism: Extensively metabolized in the liver to the active drug penciclovir (98.5%) and other inactive metabolites.
Excretion: Primarily eliminated in the urine.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug. Use cautiously in patients with impaired renal or hepatic function.

Interactions
Drug-drug. Probenecid or other drugs significantly eliminated by active renal tubular secretion: May increase famciclovir levels. Monitor patient for increased adverse effects.

Adverse reactions
CNS: headache, fatigue, dizziness, paresthesia, somnolence, fever, pain.
EENT: pharyngitis, sinusitis.
GI: diarrhea, nausea, vomiting, constipation, anorexia, abdominal pain.
Musculoskeletal: back pain, arthralgia.
Skin: pruritus; zoster-related signs, symptoms, and complications.
Other: injury, rigors.

Effects on lab test results
• May increase BUN, creatinine, AST, ALT, amylase, lipase, and bilirubin levels.
• May decrease hemoglobin and WBC and neutrophil counts.

Overdose and treatment
No acute overdose reported.
 Give symptomatic and supportive therapy. It isn’t known whether hemodialysis removes famciclovir from the blood. However, hemodialysis enhances elimination of acyclovir, a related nucleoside analogue.

Special considerations
• Drug may be given without regard to meals.
• Monitor renal and liver function test results.
Pregnant patients
• Use drug during pregnancy only when clearly indicated.
Breast-feeding patients
• It isn’t known whether drug appears in breast milk. Use cautiously in breast-feeding women.
Pediatric patients
• Safety and effectiveness haven’t been established in children younger than age 18.

Patient education
• Explain that treatment is more effective when started at earliest signs or symptoms.
• Inform patient that drug isn’t a cure for genital herpes but can decrease the duration and severity of symptoms.
• Advise patient of potential adverse reactions.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use