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Famciclovir

Pronunciation

Pronunciation: fam-SYE-kloe-vir
Class: Antiherpes virus agent

Trade Names

Famvir
- Tablets, oral 125 mg
- Tablets, oral 250 mg
- Tablets, oral 500 mg

Apo-Famciclovir (Canada)
PMS-Famciclovir (Canada)
Sandoz Famciclovir (Canada)

Pharmacology

Converts to penciclovir, which inhibits viral DNA replication by interfering with viral DNA polymerase.

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Pharmacokinetics

Absorption

Bioavailability is approximately 77%. T max is 0.9 h. AUC 0-∞ is 2.24 to 17.9 mcg•h/mL, depending on dose. C max is 0.8 to 6.6 mcg/mL, depending on dose.

Distribution

Vd is approximately 1.08 L/kg; less than 20% bound to plasma proteins.

Metabolism

Metabolized in the liver; deacetylated and oxidized to form inactive penciclovir metabolites.

Elimination

73% and 27% of administered radioactivity were recovered in the urine and feces over 72 h, respectively. Plasma Cl is approximately 36.6 L/h; approximately 75% is renally cleared. The half-life is approximately 2 to 3 h.

Special Populations

Renal Function Impairment

With CrCl 40 to 59 mL/min, Cl is approximately 13 L/h and half-life is approximately 3.4 h. With CrCl 20 to 39 mL/min, Cl is about approximately 4.2 L/h and half-life is approximately 6.2 h. With CrCl less than 20 mL/min, Cl is approximately 1.6 L/h and half-life is approximately 13.4 h.

Hepatic Function Impairment

Penciclovir C max decreased 44% and T max increased 0.75 h in patients with hepatic impairment. The pharmacokinetics of penciclovir have not been evaluated in patients with severe uncompensated hepatic impairment.

Elderly

Mean penciclovir AUC was 40% higher, and penciclovir renal Cl was 22% lower in elderly volunteers.

Children

There are no pharmacokinetic data in children to support a famciclovir dose that provides penciclovir exposure comparable with the penciclovir systemic exposures in adults after a single dose of 1,500 mg.

Gender

AUC of penciclovir was approximately 9.3 mcg•h/mL and 11.1 mcg•h/mL in male and female volunteers, respectively, after a single 500 mg dose. Penciclovir renal Cl was 28.5 L/h and 21.8 L/h, respectively.

Race

There were no significant differences in the pharmacokinetics of penciclovir between black and white subjects.

Indications and Usage

Treatment of herpes zoster (shingles) in immunocompetent patients; treatment or suppression of recurrent genital herpes in immunocompetent patients; treatment of recurrent episodes of orolabial or genital herpes in HIV-infected adults; treatment of recurrent herpes labialis (cold sores) in immunocompetent patients.

Contraindications

Hypersensitivity to famciclovir, other components of the formulation, or penciclovir.

Dosage and Administration

Herpes Zoster
Adults

PO 500 mg every 8 h for 7 days. Efficacy has not been established when initiated more than 72 h after onset of rash.

Recurrent Genital Herpes
Adults

PO 1,000 mg twice daily for 1 day. Efficacy not established when treatment is started more than 6 h after onset of symptoms or lesions.

Recurrent Herpes Labialis
Adults

PO 1,500 mg as a single dose.

Recurrent Orolabial or Genital Herpes in HIV-Infected Patients
Adults

PO 500 mg twice daily for 7 days. Efficacy not established when treatment is initiated more than 48 h after onset of symptoms or lesion.

Suppression of Recurrent Genital Herpes

PO 250 mg twice daily. Safety and efficacy not established for the suppression of recurrent genital herpes beyond 1 y.

Renal Function Impairment
Adults Herpes Zoster

PO For CrCl 40 to 59 mL/min, 500 mg every 12 h; for CrCl 20 to 39 mL/min, 500 mg every 24 h; for CrCl less than 20 mL/min, 250 mg every 24 h; for hemodialysis, 250 mg following each dialysis.

Recurrent Genital Herpes

PO For CrCl 40 to 59 mL/min, 500 mg every 12 h for 1 day; for CrCl 20 to 39 mL/min, 500 mg single dose; for CrCl less than 20 mL/min, 250 mg single dose; for hemodialysis, 250 mg single dose following dialysis.

Recurrent Herpes Labialis

PO For CrCl 40 to 59 mL/min, 750 mg single dose; for CrCl 20 to 39 mL/min, 500 mg single dose; for CrCl less than 20 mL/min, 250 single dose; for hemodialysis, 250 mg single dose following dialysis.

Recurrent Orolabial or Genital Herpes in HIV-Infected Patients

PO For CrCl 20 to 39 mL/min, 500 mg every 24 h; for CrCl less than 20 mL/min, 250 mg every 24 h; for hemodialysis, 250 mg following each dialysis.

Suppression of Recurrent Genital Herpes

PO For CrCl 20 to 39 mL/min, 125 mg every 12 h; for CrCl less than 20 mL/min, 125 mg every 24 h; for hemodialysis, 125 mg following each dialysis.

General Advice

  • Administer without regard to meals. Administer with food if GI upset occurs.
  • Initiate treatment at first sign or symptom or immediately after diagnosis.

Storage/Stability

Store between 59° and 86°F.

Drug Interactions

Following oral administration, famciclovir undergoes rapid conversion to penciclovir.

Drugs metabolized by aldehyde oxidase

The conversion of 6-deoxy penciclovir to penciclovir is catalyzed by aldehyde oxidase. Interactions with other drugs metabolized by this enzyme could potentially occur.

Probenecid or other drugs significantly eliminated by active renal tubular secretion

May increase penciclovir serum concentrations.

Adverse Reactions

CNS

Headache (39%); fatigue (5%); migraine, paresthesia (3%); confusion, confusional state, delirium, disorientation, dizziness, hallucinations, somnolence (postmarketing).

Dermatologic

Pruritus (4%); rash (3%); erythema multiforme, Stevens-Johnson syndrome, TEN, urticaria (postmarketing).

GI

Nausea (13%); diarrhea (9%); flatulence, vomiting (5%).

Genitourinary

Dysmenorrhea (8%).

Hematologic-Lymphatic

Neutropenia (3%); leukopenia (1%); thrombocytopenia (postmarketing).

Hepatic

Abnormal LFTs, cholestatic jaundice (postmarketing).

Lab Tests

Elevated lipase (5%); elevated ALT (3%); elevated AST, lipase, total bilirubin (2%).

Precautions

Pregnancy

Category B .

Lactation

Undetermined.

Children

Safety and efficacy not established.

Elderly

Use with caution.

Renal Function

Cases of acute renal failure have been reported in these patients. Dosage adjustment is recommended when CrCl is 60 mL/min or less.

Hepatic Function

No dosage adjustment is recommended for patients with well-compensated hepatic impairment.

Special Risk Patients

Efficacy not established for the treatment of chicken pox, ophthalmic zoster, in patients with first episode of genital herpes, immunocompromised patients other than for the treatment of recurrent orolabial or genital herpes in HIV-infected patients, or in black patients with recurrent genital herpes.

Genital herpes

Sexual intercourse must be avoided when lesions are present. Use of famciclovir does not prevent transmission.

Patient Information

  • Inform patients that if they experience dizziness, somnolence, confusion, or other CNS disturbances while taking famciclovir, they should refrain from driving or operating machinery.
  • Advise patients with rare hereditary problems of galactose intolerance, severe lactase deficiency, or glucose-galactose malabsorption that famciclovir contains lactose.
  • Advise patients to initiate treatment at the earliest sign or symptom of a recurrence of cold sores (eg, tingling, itching, burning, pain, lesion). Instruct patients that treatment for cold sores should not exceed 1 dose. Inform patients that famciclovir is not a cure for cold sores.
  • Inform patients that famciclovir is not a cure for genital herpes. There are no data evaluating whether famciclovir will prevent transmission of infection to others. Because genital herpes is an STD, patients should avoid contact with lesions or intercourse when lesions or symptoms are present to avoid infecting partners. Genital herpes can also be transmitted in the absence of symptoms through asymptomatic viral shedding. If medical management of recurrent episodes is indicated, advise patients to initiate therapy at the first sign or symptom.
  • Advise patients to initiate treatment as soon as possible after a diagnosis of herpes zoster.

Copyright © 2009 Wolters Kluwer Health.

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