How it is administered

Famciclovir is taken by mouth in the form of tablets. The tablets are available in strengths of 125 mg, 250 mg, and 500 mg. It can be taken with or without food, and the dosing depends on the specific condition being treated. For example, for herpes zoster (shingles), the usual dose is 500 mg every 8 hours for 7 days. For recurrent genital herpes, it may be 1000 mg twice daily for 1 day, or for suppressive therapy, 250 mg twice daily. For people with kidney problems, the dose may need to be adjusted.

How it works

Famciclovir is an antiviral medication. After you take it, your body converts it into penciclovir, which is the active form. Penciclovir works by blocking the action of an enzyme called DNA polymerase in certain viruses, specifically herpes viruses like herpes simplex virus (HSV) and varicella zoster virus (VZV). By blocking this enzyme, famciclovir prevents the virus from making new copies of itself, which helps to control the infection and reduce symptoms.

In people with weakened immune systems, such as those with blood cancers or HIV, herpes virus infections can be more frequent and severe. Famciclovir helps to reduce the number and severity of outbreaks, and can also be used to suppress ongoing viral activity. While it does not cure herpes infections, it helps manage the symptoms and reduce the risk of complications.

Who Should take it

Famciclovir is used to treat viral infections caused by herpes viruses, such as shingles (herpes zoster), recurrent genital herpes, and cold sores (herpes labialis). It is also used for suppressive therapy to prevent frequent outbreaks of genital herpes. In people with HIV, it can be used to treat recurrent episodes of orolabial or genital herpes.

For patients with blood cancers, famciclovir may be prescribed if they are at risk for or develop herpes virus infections, since their immune systems can be weakened by the cancer or its treatment. It is important to start treatment as soon as possible after symptoms begin for the best results.

Who should not take it

You should not take famciclovir if you have had an allergic reaction to famciclovir, penciclovir (the active form), or any of the ingredients in the tablet. People who have had a severe allergic reaction to Denavir® (penciclovir cream) should also avoid famciclovir.

Caution is needed for people with severe kidney problems, and the dose may need to be adjusted. If you have rare hereditary problems of galactose intolerance, severe lactase deficiency, or glucose-galactose malabsorption, you should talk to your healthcare provider before taking famciclovir, as the tablets contain lactose.

Commonly used with

Famciclovir is sometimes used along with other antiviral medications in people with weakened immune systems, such as those with blood cancers or HIV. It is also commonly used as part of supportive care in patients receiving chemotherapy or stem cell transplants, to prevent or treat herpes virus reactivation.

It may be given alongside medications for pain control or other supportive treatments, depending on the patient's needs.

Commonly tested with

In clinical studies, famciclovir has been compared to other antiviral medications such as acyclovir for the treatment of herpes virus infections. It has also been studied in combination with antiretroviral medications in HIV-infected patients.

In patients with blood cancers, famciclovir may be tested as part of infection prevention protocols, especially in those undergoing intensive chemotherapy or stem cell transplantation.