Famciclovir

Pronunciation

(fam SYE kloe veer)

U.S. Brand Names

Famvir®

Generic Available

Canadian Brand Names

Famvir®

Use

Management of acute herpes zoster (shingles) and recurrent episodes of genital herpes; treatment of recurrent herpes simplex in immunocompetent patients

Pregnancy Risk Factor

Pregnancy Implications

Use only if the benefit to the patient clearly exceeds the potential risk to the fetus.

Lactation

Excretion in breast milk unknown/contraindicated

Contraindications

Hypersensitivity to famciclovir or any component of the formulation

Warnings/Precautions

Has not been established for use in initial episodes of genital herpes, patients with ophthalmic or disseminated zoster, or in immunocompromised patients with herpes zoster; dosage adjustment is required in patients with renal insufficiency (Clcr<60 mL/minute) and in patients with noncompensated hepatic disease; safety and efficacy have not been established in children <18 years of age; animal studies indicated increases in incidence of carcinomas, mutagenic changes, and decreases in fertility with extremely large doses

Adverse Reactions

1% to 10%:

Central nervous system: Fatigue (4% to 6%), fever (1% to 3%), dizziness (3% to 5%), somnolence (1% to 2%), headache

Dermatologic: Pruritus (1% to 4%)

Gastrointestinal: Diarrhea (4% to 8%), vomiting (1% to 5%), constipation (1% to 5%), anorexia (1% to 3%), abdominal pain (1% to 4%), nausea

Neuromuscular & skeletal: Paresthesia (1% to 3%)

Respiratory: Sinusitis/pharyngitis (2%)

<1%: Rigors, arthralgia, upper respiratory infection

Overdosage/Toxicology

Supportive and symptomatic care is recommended. Hemodialysis may enhance elimination.

Drug Interactions

Increased effect/toxicity:

Cimetidine: Penciclovir AUC may increase due to impaired metabolism

Digoxin: Cmax of digoxin increases by ~19%

Probenecid: Penciclovir serum levels significantly increase

Theophylline: Penciclovir AUC/Cmax may increase and renal clearance decrease, although not clinically significant

Ethanol/Nutrition/Herb Interactions

Food: Rate of absorption and/or conversion to penciclovir and peak concentration are reduced with food, but bioavailability is not affected.

Mechanism of Action

After undergoing rapid biotransformation to the active compound, penciclovir, famciclovir is phosphorylated by viral thymidine kinase in HSV-1, HSV-2, and VZV-infected cells to a monophosphate form; this is then converted to penciclovir triphosphate and competes with deoxyguanosine triphosphate to inhibit HSV-2 polymerase (ie, herpes viral DNA synthesis/replication is selectively inhibited)

Pharmacodynamics/Kinetics

Absorption: Food decreases maximum peak concentration and delays time to peak; AUC remains the same

Distribution: Vdss: 0.98-1.08 L/kg

Protein binding: 20%

Metabolism: Rapidly deacetylated and oxidized to penciclovir; not via CYP

Bioavailability: 77%

Half-life elimination: Penciclovir: 2-3 hours (10, 20, and 7 hours in HSV-1, HSV-2, and VZV-infected cells, respectively); prolonged with renal impairment

Time to peak: 0.9 hours; Cmax and Tmax are decreased and prolonged with noncompensated hepatic impairment

Excretion: Urine (>90% as unchanged drug)

Dosage

Initiate therapy as soon as herpes zoster is diagnosed: Adults: Oral:

Acute herpes zoster: 500 mg every 8 hours for 7 days

Recurrent herpes simplex in immunocompetent patients: 125 mg twice daily for 5 days

Genital herpes:

First episode: 250 mg 3 times/day for 7-10 days

Recurrent episodes: 125 mg twice daily for 5 days

Prophylaxis: 250 mg twice daily

Severe (hospitalized patients): 250 mg twice daily

Dosing interval in renal impairment :

Herpes zoster:

Clcr 60 mL/minute: Administer 500 mg every 8 hours

Clcr 40-59 mL/minute: Administer 500 mg every 12 hours

Clcr 20-39 mL/minute: Administer 500 mg every 24 hours

Clcr<20 mL/minute: Administer 250 mg every 24 hours

Recurrent genital herpes:

Clcr 40 mL/minute: Administer 125 mg every 12 hours

Clcr 20-39 mL/minute: Administer 125 mg every 24 hours

Clcr<20 mL/minute: Administer 125 mg every 48 hours

Suppression of recurrent genital herpes:

Clcr 40 mL/minute: Administer 250 mg every 12 hours

Clcr 20-39 mL/minute: Administer 125 mg every 12 hours

Clcr<20 mL/minute: Administer 125 mg every 24 hours

Recurrent orolabial or genital herpes in HIV-infected patients:

Clcr 40 mL/minute: Administer 500 mg every 12 hours

Clcr 20-39 mL/minute: Administer 500 mg every 24 hours

Clcr<20 mL/minute: Administer 250 mg every 24 hours

Monitoring Parameters

Periodic CBC during long-term therapy

Dietary Considerations

May be taken with food or on an empty stomach.

Patient Education

Inform prescriber of all prescriptions, OTC medications, or herbal products you are taking, and any allergies you have. Take for prescribed length of time, even if condition improves. Do not discontinue without consulting prescriber. This is not a cure for genital herpes. May cause mild GI disturbances (eg, nausea, vomiting, constipation, diarrhea), fatigue, headache, or muscle aches and pains. If these are severe, contact prescriber. Breast-feeding precaution: Do not breast-feed.

Additional Information

Most effective if therapy is initiated within 72 hours of initial lesion.

Dental Health: Effects on Dental Treatment

No significant effects or complications reported

Dental Health: Vasoconstrictor/Local Anesthetic Precautions

No information available to require special precautions

Mental Health: Effects on Mental Status

May cause sedation

Mental Health: Effects on Psychiatric Treatment

None reported

Oncology: Emetic Potential

Low (10% to 30%)

Dosage Forms

Tablet: 125 mg, 250 mg, 500 mg

References

Alrabiah FA and Sacks SL, "New Antiherpesvirus Agents. Their Targets and Therapeutic Potential," Drugs , 1996, 52(1):17-32.

Boike SC, Pue MA, and Freed MI, "Pharmacokinetics of Famciclovir in Subjects With Varying Degrees of Renal Impairment," Clin Pharmacol Ther , 1994, 55(4):418-26.

Boyd MR, Safrin S, and Kern ER, "Penciclovir: A Review of Its Spectrum of Activity, Selectivity, and Cross Resistance Pattern," Antiviral Chem Chemother , 1993, 4:3-11.

Daniels S and Schentag JJ, "Drug Interaction Studies and Safety of Famciclovir in Healthy Volunteers: A Review." Antiviral Chem Chemother , 1993, 4:57-64.

De Clercq E, "Antivirals for the Treatment of Herpesvirus Infections," J Antimicrob Chemother , 1993, 32(Suppl A):121-32.

Gill KS and Wood MJ, "The Clinical Pharmacokinetics of Famciclovir," Clin Pharmacokinet , 1996, 31(1):1-8.

Goffin E, Horsmans Y, Pirson Y, et al, "Acute Necrotico-Hemorrhagic Pancreatitis After Famciclovir Prescription," Transplantation , 1995, 59(8):1218-9.

Hodge RA, "Famciclovir and Penciclovir: The Mode of Action of Famciclovir Including Its Conversion to Penciclovir," Antiviral Chem Chemother , 1993, 4:67-84.

Luber AD and Flaherty JF Jr, "Famciclovir for Treatment of Herpesvirus Infections," Ann Pharmacother , 1996, 30(9):978-85.

Perry CM and Wagstaff AJ, "Famciclovir. A Review of Its Pharmacological Properties and Therapeutic Efficacy in Herpesvirus Infections," Drugs , 1995, 50(2):396-415.

Pue MA and Benet LZ, "Pharmacokinetics of Famciclovir in Man," Antiviral Chem Chemother , 1993, 4(Suppl 1):47-55.

Sacks SL, "Genital Herpes Simplex Virus and Its Treatment Focus on Famciclovir," Semin Dermatol , 1996, 15(2 Suppl 1):32-6.

Tyring SK, Barbarash RA, Nahlik JE, et al, "Famciclovir for the Treatment of Acute Herpes Zoster: Effects on Acute Disease and Postherpetic Neuralgia," Ann Intern Med , 1995, 123(2):89-96.

Tyring SK, "Efficacy of Famciclovir in the Treatment of Herpes Zoster," Semin Dermatol , 1996, 15(2 Suppl 1):27-31.

International Brand Names

Ancivin® (ES); Bencavir® (LU); Famciclovir Padro® (ES); Famciclovir Visfarm® (ES); Famtrex® (IN); Famvir® (AT, AU, BE, CA, CH, DE, DK, EC, ES, FI, GB, HR, HU, IE, IL, IT, KW, LU, NL, NO, PL, RO, RU, SE, SG, TH, TR, ZA); Oravir® (FR); Pentavir® (AR); Penvir® (BR); Vectavir® (LU)

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