Famvir

Action

Converts to penciclovir and selectively inhibits DNA polymerase and viral DNA synthesis

Availability

Tablets: 125 mg, 250 mg, 500 mg

Indications and dosages

➣ Acute herpes zoster infection (shingles)

Adults: 500 mg P.O. q 8 hours for 7 days

➣ Recurrent genital herpes in immunocompetent patients

Adults: 1,000 mg P.O. b.i.d. for 1 day, starting as soon as symptoms appear

➣ Suppression of recurrent genital herpes

Adults: 250 mg P.O. b.i.d. for up to 1 year

➣ Recurrent herpes simplex infection in patients with human immunodeficiency virus

Adults: 500 mg P.O. b.i.d. for 7 days

➣ Herpes labialis (oral herpes simplex) in immunocompetent patients

Adults: 1,500 mg P.O. as a one-time dose given as soon as symptoms appear

Dosage adjustment

• Renal impairment

Contraindications

• Hypersensitivity to drug or its components

Precautions

Use cautiously in:

• renal or hepatic impairment

• elderly patients

• pregnant or breastfeeding patients

• children younger than age 18.

Administration

• Know that for best response, therapy should begin within 6 hours of onset of genital herpes symptoms or lesions.

• Give with or without food.

Adverse reactions

CNS: headache, fatigue, dizziness, drowsiness, paresthesia, insomnia

EENT: pharyngitis, sinusitis

GI: nausea, vomiting, diarrhea, constipation, abdominal pain, anorexia

Musculoskeletal: back pain, joint pain

Skin: pruritus, rash

Other: fever

Interactions

Drug-drug. Digoxin: increased digoxin blood level, increased risk of toxicity

Probenecid: increased blood level of penciclovir (active antiviral compound of famciclovir)

Patient monitoring

• When giving concurrently with digoxin, monitor digoxin blood level and evaluate for digoxin toxicity.

• Monitor CBC, blood urea nitrogen, creatinine, and electrolyte levels.

• Be aware that drug may take several weeks to reach therapeutic level.

• Know that renal failure may raise blood drug level, increasing the risk of adverse reactions.

• Avoid direct contact with infected areas. Wash hands frequently and wear gloves during patient contact.

Patient teaching

• Instruct patient to take with food or milk to avoid upset stomach.

• Inform patient that drug doesn't cure herpes but only decreases pain and itching by allowing sores to heal and preventing new ones from forming.

• Advise patient to wear loose-fitting clothing to avoid irritating lesions.

• Tell patient to report rash or itching.

• Instruct female patient to tell prescriber if she is pregnant or breastfeeding.

• As appropriate, review all other significant adverse reactions and interactions, especially those related to the drugs mentioned above.