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Pharmacologic class: Synthetic nucleoside
Therapeutic class: Antiviral
Pregnancy risk category B
Converts to penciclovir and selectively inhibits DNA polymerase and viral DNA synthesis
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
• Renal impairment
• Hypersensitivity to drug or its components
Use cautiously in:
• renal or hepatic impairment
• elderly patients
• pregnant or breastfeeding patients
• children younger than age 18.
• Know that for best response, therapy should begin within 6 hours of onset of genital herpes symptoms or lesions.
• Give with or without food.
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
Drug-drug. Digoxin: increased digoxin blood level, increased risk of toxicity
Probenecid: increased blood level of penciclovir (active antiviral compound of famciclovir)
• 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.
• 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.