Dosing and uses of Famvir (famciclovir)
Adult dosage forms and strengths
tablet
- 125mg
- 250mg
- 500mg
Acute Herpes Zoster (Shingles)
Treatment in immunocompetent adults
500 mg PO q8hr for 7 days; initiated within 72 hours of symptom or lesion onset
Herpes Labialis
Treatment of initial and recurrent episodes or suppressive therapy in immunocompetent adults
Initial episode: 250 mg PO q8hr for 7-10 days
Suppressive therapy: 250 mg PO q12hr for 12 months
Recurrent episodes: 1500 mg PO once; initiate therapy at first sign (within 1 hour) of symptoms such as tingling, itching or burning
Genital Herpes
Treatment of initial and recurrent episodes or suppressive therapy in immunocompetent adults
Initial episode (off-label): 250 mg PO q8hr for 7-10 days
Suppressive therapy: 250 mg PO q12hr for up to 12 months
Recurrent episodes: 1000 mg PO q12hr for 1 day; initiated within 6 hours of symptom or lesion onset
Herpes (HIV-Infected Adults)
Prevention of herpes simplex virus (HSV) reactivation and treatment of recurrent episodes
Prevention of HSV reactivation: 500 mg PO q12hr
Recurrent episodes: 500 mg PO q12hr for 5-10 days; initiated within 48 hours of symptom or lesion onset
Dosing Modifications
Acute herpes zoster
- CrCl ≥60 mL/min: Regular dosage
- CrCl 40-59 mL/min: 500 mg q12hr
- CrCl 20-39 mL/min: 500 mg once daily
- CrCl <20 mL/min: 250 mg once daily
- Hemodialysis: 250 mg after each session
Herpes labialis
- CrCl ≥60 mL/min: Regular dosage
- CrCl 40-59 mL/min: 750 mg once
- CrCl 20-39 mL/min: 500 mg once
- CrCl <20 mL/min: 250 mg once
- Hemodialysis: 250 mg once after dialysis
Genital herpes (treatment of recurrent disease)
- CrCl ≥60 mL/min: Regular dosage
- CrCl 40-59 mL/min: 500 mg q12hr for 1 day (2 doses total)
- CrCl 20-39 mL/min: 500 mg once
- CrCl <20 mL/min: 250 mg once
- Hemodialysis: 250 mg once after dialysis
Genital herpes (suppressive therapy)
- CrCl ≥40 mL/min: Regular dosage
- CrCl 20-39 mL/min: 125 mg q12hr
- CrCl <20 mL/min: 125 mg/day
- Hemodialysis: 125 mg after each session
Herpes (HIV-infected adults)
- CrCl ≥40 mL/min: Regular dosage
- CrCl 20-39 mL/min: 500 mg/day
- CrCl <20 mL/min: 250 mg/day
- Hemodialysis: 250 mg after each session
Pediatric dosage forms and strengths
tablet
- 125mg
- 250mg
- 500mg
Genital Herpes (Off-label)
Treatment of initial and recurrent episodes or suppressive therapy
<18 years: Safety and efficacy not established; may be considered in adolescents
Initial episode: 250 mg PO q8hr for 7-10 days
Suppressive therapy: 250 mg PO q12hr for up to 12 months
Recurrent episodes: 125 mg PO q12hr for 3-5 days
Renal impairment: As for adults; see Dosing Modifications
Famvir (famciclovir) adverse (side) effects
>10%
Headache (23%)
Nausea (13%)
1-10%
Diarrhea (2-9%)
Abdominal pain (8%)
Dysmenorrhea (<8%)
Vomiting (1-5%)
Flatulence (5%)
Pruritus (4%)
Rash (3%)
Paresthesia (3%)
Neutropenia (3%)
Increased transaminases (2-3%)
Increased bilirubin (2%)
Fatigue (1%)
<1%
Arthralgia
Confusion
Dizziness
Erythema multiforme
Hallucinations
Jaundice
Rigors
Thrombocytopenia
Upper respiratory tract infection
Postmarketing Reports
Blood and lymphatic system disorders: Thrombocytopenia
Immune system disorders anaphylactic shock and anaphylactic reaction under
Hepatobiliary disorders: Abnormal liver function tests, cholestatic jaundice
Nervous system disorders: Dizziness, somnolence, seizures
Psychiatric disorders: Confusion (including delirium, disorientation, and confusional state occurring predominantly in the elderly), hallucinations
Skin and subcutaneous tissue disorders: Urticaria, Stevens-Johnson syndrome, toxic epidermal necrolysis, angioedema (eg, face, eyelid, periorbital, pharyngeal edema), hypersensitivity vasculitis
Cardiac disorders: Palpitations
Warnings
Contraindications
Known hypersensitivity to this drug or its active metabolite, penciclovir
Cautions
Dosage must be adjusted in renal impairment; there is a risk of acute renal failure (ARF) with inappropriately high dosage
Patients with galactose intolerance, glucose-galactose malabsorption syndrome, or severe lactase deficiency should discuss it with practitioner (famciclovir tablets contain lactose)
Pregnancy and lactation
Pregnancy category: B
Lactation: Unknown whether drug is excreted in breast milk; caution advised
Pregnancy registry: Pregnant women exposed to famciclovir should enroll by calling 1-888-669-6682
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Famvir (famciclovir)
Mechanism of action
Prodrug of penciclovir, which selectively inhibits viral DNA replication in herpes simplex virus (HSV) type 1 (HSV-1), HSV-2, and varicella zoster virus (VZV)
Absorption
Bioavailability: 77%
Peak plasma time: 1 hr (penciclovir)
Food decreases Cmax and delays Tmax but does not change AUC
Distribution
Protein bound: <20% (penciclovir)
Vd: 0.91-1.25 L/kg
Metabolism
Rapidly deacetylated and oxidized to penciclovir; not metabolized via CYP isoenzymes
Metabolites: Penciclovir triphosphate (active)
Elimination
Half-life (penciclovir): 2-4 hr; prolonged with renal impairment
Excretion: Urine (73%), feces (27%)
