Famvir

What is Famvir?

Famvir, with the active ingredient famciclovir, is an antiviral medication used to treat infections caused by certain types of viruses. It is specifically indicated for the treatment of herpes zoster (shingles), genital herpes, and cold sores (herpes labialis). Famvir is a prodrug that, once ingested, is converted to penciclovir in the body.

Available Dosage Forms

Famvir is available in tablet form in various strengths including 125 mg, 250 mg, and 500 mg for oral administration. The tablet is to be swallowed whole with water and can be taken with or without food.

Pharmacological Action

Upon oral administration, famciclovir undergoes rapid conversion to penciclovir by hepatic first-pass metabolism. Penciclovir then inhibits viral DNA polymerase, thereby blocking viral DNA synthesis without affecting normal cellular processes. This action helps to limit the spread of the virus and aids in the reduction of the duration and severity of symptoms.

Indications and Usage

Famvir is indicated for the treatment of acute herpes zoster (shingles) in adult patients. It is also used for the treatment of recurrent episodes of genital herpes and for the suppression of recurrent episodes in adult patients. Additionally, it is used for the treatment of recurrent herpes labialis (cold sores) in immunocompetent patients.

Dosing Information

The dosing of Famvir varies based on the indication. For herpes zoster, the typical dose is 500 mg every 8 hours for 7 days. For recurrent genital herpes, the dose can be 125 mg twice daily for 5 days, and for suppressive therapy, 250 mg twice daily. For recurrent herpes labialis, a single dose of 1500 mg is usually recommended. Dose adjustment may be required for patients with renal impairment.

Administration Guidelines

It is recommended to start treatment with Famvir at the first sign or symptom of a herpes virus infection. For the best efficacy in herpes zoster, initiate treatment within 48 to 72 hours of the onset of the rash. For recurrent herpes labialis, treatment should begin at the earliest sign of a cold sore.

Drug Interactions

Famvir should be used cautiously with drugs that affect renal function as it is renally excreted. Probenecid and other drugs that compete for active tubular secretion may increase the plasma levels of penciclovir. Famvir should be used with caution when co-administered with these drugs.

Adjustment for Renal Impairment

For patients with renal impairment, including those on hemodialysis or chronic kidney disease, dosage adjustment is advised. Decreased doses or increased dosing intervals may be required based on the extent of renal impairment to prevent accumulative toxicity of penciclovir.

Pediatric Use

The safety and effectiveness of Famvir have not been established in pediatric patients. Therefore, its use in individuals under 18 is not recommended unless the potential benefit outweighs the potential risks.

Pregnancy and Lactation

Famvir should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. There is no adequate data on the transfer of famciclovir or its metabolites into human milk, hence caution should be exercised when Famvir is administered to a nursing mother.

Geriatric Use

In geriatric patients, consideration should be given to renal function, as this population may have decreased renal function. Appropriate dosage adjustments may be necessary to accommodate this change in renal function.

Common Adverse Reactions

The most common side effects associated with Famvir include headache, nausea, and diarrhea. Less frequently, vomiting, fatigue, and dizziness have been reported. The incidence and severity of adverse reactions may vary according to the indication for which Famvir is being prescribed.

Overdosage Management

In cases of Famvir overdosage, the patient should be monitored for signs of toxicity, and standard supportive treatment applied as necessary. Because Famvir is dialyzable, hemodialysis may be considered in cases of significant overdosage, especially in patients with compromised renal function.

Storage Conditions

Famvir tablets should be stored at room temperature between 15-30°C (59-86°F). Protect from light and moisture, and keep out of reach of children and pets to avoid accidental ingestion.

Dispensing Instructions

When dispensing Famvir, pharmacists should ensure that the correct dosage strength is given according to the prescribed therapy. It is important to counsel patients on administration instructions, potential side effects, and the importance of completing the prescribed course of therapy.