Famvir®

(famciclovir)
Tablets

 

See also:  Denavir  Valtrex

 

Drug Uses
Famvir is an oral antiviral prescription medication that is prescribed for: treatment of recurrent genital herpes in otherwise healthy patients; suppression of recurrent genital herpes in otherwise healthy patients; treatment of recurrent herpes simplex virus infections (genital herpes and cold sores) in HIV-infected patients and herpes zoster (shingles).

How Taken
Famvir can be prescribed in one of three ways:

 

1. Episodic treatment: your doctor treats an outbreak of genital herpes as it occurs. The usual dose of Famvir is one 125-mg pill, twice a day, for 5 days.

2. Suppressive treatment: if you have frequent or severe outbreaks, you take one 250-mg pill, twice a day, for up to 1 year to suppress the genital herpes virus and help to prevent outbreaks.

3. Patients with HIV: Famvir is the only prescription oral antiviral therapy indicated for treating genital. In patients with herpes simplex and HIV, the dose of Famvir is 500 mg, twice a day, for 7 days.

Famvir can be taken with or without food.

Warnings/Precautions
Do not take Famvir if you are allergic to penciclovir (Denavir) without first talking to your doctor. Before taking this medication, tell your doctor if you have kidney disease. You may need a dosage adjustment or special monitoring during treatment with Famvir. Famvir (Pregnancy Category B) should be used during pregnancy only if the benefit to the patient clearly exceeds the risk to the fetus.

Missed Dose
IF YOU MISS A DOSE OF THIS MEDICINE, take it as soon as possible. If it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do NOT take 2 doses at once.

Possible Side Effects
Stop taking Famvir and seek emergency medical attention if you experience an allergic reaction (difficulty breathing; closing of your throat; swelling of your lips, tongue, or face; or hives). Other, less serious side effects may be more likely to occur. Continue to take Famvir and talk to your doctor if you experience nausea or vomiting, a headache, diarrhea, dizziness, tingling in your hands or feet, or itching.

Storage
Store between 15C and 30C (59F and 86F) and out of reach of children.

Overdose
Seek emergency medical attention. A Famvir overdose has no known symptoms, but an overdose of acyclovir (Zovirax), which is a similar drug, may cause seizures, hallucinations, and kidney damage (decreased urine production).

More Information
Treatment with Famvir should be started as soon as possible after the first appearance of symptoms (e.g. tingling, burning, blisters). Take all of the Famvir that has been prescribed for you even if you begin to feel better. Your symptoms may start to improve before the infection is completely treated. Herpes infections are contagious and you can infect other people, even during treatment. Avoid letting infected areas come into contact with other people. Wash your hands frequently to prevent transmission. For more information, talk to your doctor, pharmacist or health care provider.

 

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Famvir® (famciclovir) contains famciclovir, an orally administered prodrug of the antiviral agent penciclovir. Chemically, famciclovir is known as

2-[2-(2-amino-9H-purin-9-yl)ethyl]-1,3-propanediol diacetate.

 

Its molecular formula is C14H19N504; its molecular weight is 321.3. It is a synthetic acyclic guanine derivative.

 

Famciclovir is a white to pale yellow solid. It is freely soluble in acetone and methanol, and sparingly soluble in ethanol and isopropanol. At 25° C famciclovir is freely soluble (>25% w/v) in water initially, but rapidly precipitates as the sparingly soluble (2%-3% w/v) monohydrate. Famciclovir is not hygroscopic below 85% relative humidity. Partition coefficients are: octanol/water (pH 4.8) P=1.09 and octanol/phosphate buffer (pH 7.4) P=2.08.

 

Tablets for Oral Administration: Each white, film-coated tablet contains famciclovir. The 125-mg and 250-mg tablets are round; the 500-mg tablets are oval. Inactive ingredients consist of hydroxypropyl cellulose, hydroxypropyl methylcellulose, lactose, magnesium stearate, polyethylene glycols, sodium starch glycolate and titanium dioxide.

 

MICROBIOLOGY

Mechanism of Antiviral Activity: Famciclovir undergoes rapid biotransformation to the active antiviral compound penciclovir, which has inhibitory activity against herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) and varicella zoster virus (VZV). In cells infected with HSV-1, HSV-2 or VZV, viral thymidine kinase phosphorylates penciclovir to a monophosphate form that, in turn, is converted to penciclovir triphosphate by cellular kinases. In vitro studies demonstrate that penciclovir triphosphate inhibits HSV-2 DNA polymerase competitively with deoxyguanosine triphosphate. Consequently, herpes viral DNA synthesis and, therefore, replication are selectively inhibited.

Penciclovir triphosphate has an intracellular half-life of 10 hours in HSV-1-, 20 hours in HSV-2- and 7 hours in VZV-infected cells cultured in vitro; however, the clinical significance is unknown.

 

Antiviral Activity In Vitro and In Vivo: In cell culture studies, penciclovir has antiviral activity against the following herpes viruses (listed in decreasing order of potency): HSV-1, HSV-2 and VZV. Sensitivity test results, expressed as the concentration of the drug required to inhibit the growth of the virus by 50% (IC₅₀) or 99% (IC₉₉) in cell culture, vary greatly depending upon a number of factors, including the assay protocols, and in particular