Famvir (famciclovir) is an oral antiviral prodrug indicated for the management of acute herpesvirus infections and the suppression of recurrent episodes. Upon ingestion, it undergoes rapid biotransformation into the active metabolite penciclovir, which selectively inhibits viral DNA polymerase, effectively halting viral replication. This mechanism provides a potent, targeted approach to reducing lesion duration, viral shedding, and associated discomfort. It is prescribed for herpes zoster (shingles), genital herpes, and herpes labialis (cold sores) in immunocompetent and immunocompromised patients. Clinical evidence supports its efficacy in shortening healing time and decreasing the frequency of recurrences when used as suppressive therapy.

Features

• Active metabolite: penciclovir
• Mechanism: selective inhibition of viral DNA polymerase
• Bioavailability: approximately 77% following oral administration
• Half-life: 2–3 hours for penciclovir in patients with normal renal function
• Formulation: film-coated tablets (125 mg, 250 mg, 500 mg)
• Administration: oral, with or without food

Benefits

• Reduces the duration of viral shedding and lesion healing time in acute episodes
• Decreases the frequency of recurrent genital herpes outbreaks with suppressive therapy
• Alleviates associated symptoms such as pain, itching, and burning
• Provides flexible dosing regimens tailored to infection type and patient status
• Suitable for use in immunocompromised patients under medical supervision
• May reduce the risk of transmission of genital herpes to susceptible partners

Common use

Famvir is commonly prescribed for the treatment of herpes zoster (shingles) to accelerate lesion healing and reduce acute pain. It is also used for episodic treatment or suppression of recurrent genital herpes in immunocompetent adults. In immunocompromised patients, such as those with HIV, it is indicated for the treatment and suppression of recurrent herpes simplex infections. Off-label uses may include management of herpes labialis (cold sores) and prevention of cytomegalovirus reactivation in transplant recipients, though these should only be undertaken under specialist guidance.

Dosage and direction

Dosage must be individualized based on infection type, renal function, and immunologic status. For herpes zoster: 500 mg every 8 hours for 7 days. For recurrent genital herpes: 125 mg twice daily for 5 days, or 1000 mg twice daily for 1 day. For suppression of recurrent genital herpes: 250 mg twice daily. In patients with renal impairment, dosage adjustment is required. Administration should begin at the earliest sign or symptom of recurrence. Tablets should be swallowed whole with water; food does not significantly affect absorption.

Precautions

Use with caution in elderly patients and those with renal impairment; dosage adjustment is necessary. Monitor for signs of thrombotic microangiopathy in immunocompromised patients. Not recommended during pregnancy unless potential benefit justifies potential risk. Breastfeeding should be avoided due to excretion in milk. May cause dizziness or somnolence; advise patients to avoid driving or operating machinery until response is known. Ensure adequate hydration during therapy.

Contraindications

Hypersensitivity to famciclovir, penciclovir, or any component of the formulation. Concurrent administration with drugs that inhibit organic cation transporter 2 (OCT2) in patients with renal impairment. Use in patients with severe renal impairment (CrCl <30 mL/min) without appropriate dosage adjustment is contraindicated.

Possible side effect

Common adverse reactions include headache (≈9%), nausea (≈5%), diarrhea (≈4%), and fatigue (≈3%). Less frequently, dizziness, vomiting, abdominal pain, and pruritus may occur. Rare but serious effects include confusion, hallucinations, acute renal failure, thrombocytopenia, and hepatotoxicity. Allergic reactions such as rash and angioedema have been reported. In clinical trials, side effects were generally mild and self-limiting.

Drug interaction

Probenecid and other drugs inhibiting OCT2 may increase penciclovir plasma concentrations. Famvir may interact with drugs that compete for renal tubular secretion. No clinically significant interactions with cytochrome P450 enzymes are known. Use caution with other nephrotoxic agents. Always review the patient’s full medication list before prescribing.

Missed dose

If a dose is missed, it should be taken as soon as remembered unless it is almost time for the next dose. Do not double the dose. Maintaining consistent dosing is important for efficacy, especially in suppressive therapy.

Overdose

Symptoms may include nausea, vomiting, renal impairment, and neurological effects such as agitation and confusion. There is no specific antidote. Treatment is supportive and includes gastric lavage if ingestion was recent, hydration, and monitoring of renal function. Hemodialysis may remove penciclovir.

Storage

Store at room temperature (20–25°C). Keep in the original container, protected from light and moisture. Keep out of reach of children. Do not use after the expiration date printed on the packaging.

Disclaimer

This information is intended for healthcare professionals and should not replace personalized medical advice. Always consult a qualified physician for diagnosis, dosage, and treatment recommendations. Use only as directed. Individual response may vary.

Reviews

Clinical studies and post-marketing surveillance indicate high patient satisfaction with Famvir, particularly regarding reduction in outbreak duration and frequency. In randomized trials, it demonstrated superior efficacy compared to placebo in healing lesions and resolving symptoms. Healthcare providers note its favorable tolerability and convenient dosing. Long-term use for suppression is generally well-tolerated. Real-world evidence supports its role in improving quality of life for patients with recurrent herpes infections.