Famciclovir

Famciclovir is an antiviral medication for the treatment of herpes infections. It is a prodrug that is converted to penciclovir in the body and is active against herpes simplex viruses (HSV-1 and HSV-2) as well as the varicella-zoster virus.

For genital herpes, famciclovir offers advantages similar to those of valaciclovir: good absorption and a simple dosing schedule. It is an alternative for patients who do not tolerate valaciclovir.

A well-known brand name is Famvir®.

Famciclovir is activated to penciclovir in the body:

Conversion: 1. Famciclovir is converted to penciclovir in the intestine and liver 2. In infected cells, penciclovir is phosphorylated by viral thymidine kinase 3. Penciclovir triphosphate inhibits viral DNA polymerase 4. Viral DNA synthesis is blocked

Advantages:

• Good oral bioavailability (77%)
• Long intracellular half-life
• Selective action on virus-infected cells
• Little effect on healthy cells

Spectrum of activity:

• Herpes simplex type 1 and 2
• Varicella-zoster virus

Famciclovir is suitable for:

• Genital herpes – initial infection
• Genital herpes – recurrent episodes
• Suppressive therapy for frequent recurrences
• Shingles (herpes zoster)

Advantages:

• Alternative to valaciclovir
• Well tolerated
• Simple dosing schedule

Limitations:

• Does not cure herpes (the virus remains in the body)
• Not effective against other viruses
• Dose adjustment needed in renal impairment

Genital herpes – initial infection:

• 250 mg 3 times daily for 5-10 days

Genital herpes – recurrence:

• 125 mg 2 times daily for 5 days OR
• 1000 mg 2 times daily for 1 day (short-course therapy)

Suppressive therapy:

• 250 mg 2 times daily

Shingles:

• 500 mg 3 times daily for 7 days

In renal impairment: Dose reduction required depending on creatinine clearance.

How to take:

• With or without food
• With enough water
• At regular intervals between doses

During a herpes outbreak:

• Start as early as possible (at the first symptoms)
• Ideally within 24 hours of symptom onset

Suppressive therapy:

• At the same time every day
• Do not forget – gaps reduce effectiveness
• A trial discontinuation is possible after 6-12 months

Notes:

• Drink enough fluids
• Continue the treatment for the full prescribed duration even if symptoms improve

Famciclovir must not be used in cases of:

• Hypersensitivity to famciclovir or penciclovir

Dose adjustment in:

• Renal impairment (important!)

No dose adjustment needed in:

• Mild to moderate hepatic impairment
• Elderly patients without renal impairment

Severe hepatic impairment: No data are available. Famciclovir may be converted less well into its active form penciclovir and may then be less effective.

Pregnancy: Only if absolutely necessary. Less data available than for aciclovir/valaciclovir.

Breastfeeding: Not recommended (it is unknown whether it passes into breast milk).

Very common (10% or more):

• Headache

Common (1-10%):

• Nausea
• Diarrhea
• Dizziness
• Abdominal pain
• Skin rash

Uncommon:

• Fatigue
• Confusion (in elderly patients, renal impairment)

Rare:

• Hallucinations

Frequency not known:

• Severe skin reactions

Compared with aciclovir: Similar side effect profile. Gastrointestinal complaints may be slightly more common.

Interactions:

• Probenecid – increases penciclovir levels
• Other nephrotoxic medications – additive strain on the kidneys

No relevant interactions with:

• Hormonal contraception
• Most common medications

In renal impairment: Particularly important: dose adjustment required.