Favirox (Tablets) Instructions for Use

ATC Code

J05AB09 (Famciclovir)

Active Substance

Famciclovir (Rec.INN registered by WHO)

Clinical-Pharmacological Group

Antiviral drug

Pharmacotherapeutic Group

Antiviral agent

Pharmacological Action

Antiviral agent. After oral administration, Famciclovir in vivo is rapidly converted to penciclovir, which has in vivo and in vitro activity against human herpesviruses, including Varicella zoster virus and Herpes simplex types 1 and 2, as well as Epstein-Barr virus and cytomegalovirus.

Penciclovir enters virus-infected cells, where it is rapidly converted by viral thymidine kinase to monophosphate, which in turn is converted by cellular enzymes to triphosphate. Penciclovir triphosphate remains in virus-infected cells for more than 12 hours, inhibiting viral DNA synthesis and virus replication therein. The half-life of penciclovir triphosphate in cells infected with Varicella zoster and Herpes simplex is 9, 10, and 20 hours, respectively.

The concentration of penciclovir triphosphate in uninfected cells does not exceed the minimum detectable level; therefore, at therapeutic concentrations, penciclovir does not affect uninfected cells.

Penciclovir is active against recently discovered acyclovir-resistant strains of Herpes simplex virus with altered DNA polymerase.

Famciclovir significantly reduces the intensity and duration of postherpetic neuralgia in patients with herpes zoster.

In a placebo-controlled study in immunocompromised patients due to HIV infection, it was shown that Famciclovir at a dose of 500 mg twice daily reduced the number of days of Herpes simplex virus shedding (both with and without clinical manifestations).

Pharmacokinetics

After oral administration, Famciclovir is rapidly and almost completely absorbed and is rapidly converted to active penciclovir. The bioavailability of penciclovir after oral administration of famciclovir is 77%. With famciclovir doses of 125 mg, 250 mg, or 500 mg, the C_max of penciclovir is reached on average after 45 minutes.

No accumulation was observed with repeated doses of the drug. Plasma protein binding of penciclovir and its 6-deoxy precursor is less than 20%.

The T_1/2 of penciclovir from plasma in the terminal phase after single and repeated doses is about 2 hours.

Famciclovir is excreted mainly in the form of penciclovir and its 6-deoxy precursor, which are excreted unchanged in the urine; Famciclovir is not detected in the urine.

Indications

Infections caused by Varicella zoster virus (herpes zoster, including herpes zoster with ocular complications); infections caused by Herpes simplex virus (primary infection, exacerbation of chronic infection, suppression of recurrent infection).

ICD codes

Dosage Regimen

Initiate treatment immediately following diagnosis.

For herpes zoster, administer 500 mg three times daily for 7 days.

For recurrent genital herpes, administer a single 1000 mg dose twice daily for 1 day.

For herpes labialis, administer a single 1500 mg dose as a one-time regimen.

For suppression of recurrent genital herpes, administer 250 mg twice daily for up to 1 year.

For immunocompromised patients with herpes simplex, administer 500 mg twice daily for 7 days.

Adjust dosage in patients with renal impairment.

For creatinine clearance 40-59 mL/min, reduce herpes zoster dose to 500 mg twice daily.

For creatinine clearance 20-39 mL/min, reduce herpes zoster dose to 500 mg once daily.

For creatinine clearance below 20 mL/min, reduce herpes zoster dose to 250 mg once daily.

For hemodialysis patients, administer dose after the dialysis procedure.

Swallow tablets whole with water, with or without food.

Adverse Reactions

Possible mild to moderate headaches, nausea.

Rarely vomiting, dizziness, skin rash; predominantly in elderly patients – confusion, hallucinations.

In patients with reduced immunity abdominal pain, fever are possible; rarely – granulocytopenia and thrombocytopenia.

Contraindications

Hypersensitivity to famciclovir and penciclovir.

Use in Pregnancy and Lactation

Since the safety of famciclovir during pregnancy and lactation has not been studied, its use is not recommended, except in cases where the expected benefit of therapy for the mother outweighs the potential risk to the fetus or breastfed infant.

It is not known whether penciclovir is excreted in human breast milk.

Famciclovir does not have a significant effect on human sperm count, morphology, or motility.

Experimental studies have not revealed embryotoxic or teratogenic effects of famciclovir and penciclovir.

Studies in rats receiving Famciclovir orally have shown that penciclovir is excreted in breast milk.

A decrease in fertility was noted in an experimental model in male rats receiving Famciclovir at a dose of 500 mg/kg body weight; no significant decrease in fertility was observed in female rats.

Use in Renal Impairment

Use with caution in patients with impaired renal function.

Special Precautions

Use with caution in patients with impaired renal function.

In the presence of clinical manifestations of genital herpes, even if antiviral treatment is initiated, patients should avoid sexual intercourse.

Drug Interactions

Probenecid and other drugs affecting renal function may alter plasma levels of penciclovir.

Storage Conditions

Store at 2°C (36°F) to 25°C (77°F). Keep in original packaging, protected from light. Keep out of reach of children.

Dispensing Status

Rx Only

Important Safety Information

This information is for educational purposes only and does not replace professional medical advice. Always consult your doctor before use. Dosage and side effects may vary. Use only as prescribed.