Favirox®

Pharmachologic effect:

Antiviral.
Favirox® is effective for human herpes viruses, including Varicella zoster, Herpes simplex types 1 and 2, Epstein-Barr virus and cytomegalovirus.

Pharmacodynamics:

After oral administration, famciclovir is rapidly converted to penciclovir, which has activity against human herpes viruses, including Varicella zoster and Herpes simplex types 1 and 2, as well as Epstein-Barr virus and cytomegalovirus.
Penciclovir enters virus-infected cells, where, under the action of viral thymidine kinase, it quickly turns into monophosphate, which, in turn, with the participation of cellular enzymes, turns into triphosphate. Penciclovir triphosphate is present in virus-infected cells for more than 12 hours, inhibiting viral DNA synthesis and viral replication in them. The half-life of penciclovir triphosphate in cells affected by Varicella zoster, Herpes simplex is 9, 10 and 20 hours, respectively. The concentration of penciclovir triphosphate in uninfected cells does not exceed the minimum determined, therefore, at therapeutic concentrations, penciclovir has no effect on uninfected cells.
Penciclovir is active against recently discovered acyclovir-resistant strains of the Herpes simplex virus with an altered DNA polymerase.
Famciclovir significantly reduces the intensity and duration of postherpetic neuralgia in patients with herpes zoster.
In a placebo-controlled study in patients with immunodeficiency due to HIV infection, famciclovir at a dose of 500 mg 2 times / day was shown to reduce 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 rapidly converted to the active penciclovir. The bioavailability of penciclovir after oral administration of famciclovir is 77%. At doses of famciclovir 125 mg, 250 mg or 500 mg Cmax of penciclovir is reached after an average of 45 minutes.
With repeated doses of the drug, cumulation was not observed. Plasma protein binding of penciclovir and its 6-deoxy precursor is less than 20%.
T1/2 of penciclovir from plasma in the final phase after taking a single and repeated doses is about 2 hours.
Famciclovir is excreted primarily as penciclovir and its 6-deoxy precursor, which are excreted unchanged in the urine; famciclovir is not detected in the urine.

Indications:

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

Contraindications:

Hypersensitivity to famciclovir and penciclovir.

Use with caution:

Use with caution in patients with impaired renal function.

Pregnancy and breast-feeding:

Since the safety of famciclovir during pregnancy and lactation has not been studied, use is not recommended unless the expected benefit to the mother outweighs the potential risk to the fetus or infant.
It is not known whether penciclovir is excreted in human breast milk.
Famciclovir does not have a pronounced effect on the spermogram, morphology or motility of human spermatozoa.
In experimental studies, no embryotoxic and teratogenic effects of famciclovir and penciclovir were detected.

Side effects:

Possible: mild to moderate headaches, nausea.
Rarely: vomiting, dizziness, skin rash; predominantly in elderly patients - confusion, hallucinations.
In patients with reduced immunity: possible abdominal pain, fever; rarely - granulocytopenia and thrombocytopenia.

Interaction:

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

Dosing and Administration:

The frequency and duration of use depend on the indications, the state of immunity, kidney function, and the effectiveness of treatment. Recommended doses for adult patients are shown in the table below :

	in immunocompetent patients	in immunocompromised patients
VZV (Varizella-Zoster Virus) infection: herpes zoster, including herpes ophthalmos	500mg 3 times a day for 7 days	500mg 3 times a day for 10 days
HSV infection (Herpes Simplex Virus): labial herpes or genital herpes	For the first episode of genital herpes, the recommended dose is 250 mg 3 times a day for 5 days. For recurrence of genital herpes, the recommended dose is: 1000 mg 2 times a day for 1 day, or 125 mg 2 times a day for 5 days, or 500 mg once followed by three doses of 250 mg every 12 hours. With relapses of labial herpes - 1500 mg once for 1 day or 750 mg 2 times a day for 1 day.	For the first episode of genital herpes, the recommended dose is 500 mg 2 times a day for 7 days. For the prevention of exacerbation of genital herpes (suppressive therapy) - 250 mg 2 times a day. The duration of therapy depends on the severity of the disease. Periodic assessment of possible changes in the course of the disease after 12 months is recommended. In HIV-infected patients, the effective dose is 500 mg 2 times a day.

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

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