Classifications: antiviral;
Therapeutic: antiviral

Prototype: Acyclovir
Pregnancy Category: B


125 mg, 250 mg, 500 mg tablets


Prodrug of the antiviral agent penciclovir; may have an advantage over acyclovir because of its greater stability intracellularly in infected cells. Prevents viral replication by inhibition of DNA synthesis in herpes virus–infected cells.

Therapeutic Effect

Effectiveness is indicated by decreasing pain and crusting of lesions followed by loss of vesicles, ulcers, and crusts. Interferes with DNA synthesis of herpes simplex virus type 1 and 2 (HSV-1 and HSV-2) infections, varicella-zoster virus, and cytomegalovirus.


Management of acute herpes zoster, genital herpes, recurrent episodes of genital herpes in immunocompromised adults. Suppression of recurrent episodes of genital herpes in immunocompetent adults.


Hypersensitivity to famciclovir, lactation.

Cautious Use

Renal or hepatic impairment, carcinoma, older adults, pregnancy (category B). Safety in children <18 y is not established.

Route & Dosage

Herpes Zoster, Treatment
Adult: PO 500 mg q8h for 7 d, start within 48–72 h of onset of rash

Renal Impairment
Clcr 40–59 mL/min: 500 mg q12h; 20–39 mL/min: 500 mg q24h

Treatment of Recurrent Genital Herpes
Adult: PO 125 mg b.i.d. x 5 d

Suppression of Recurrent Genital Herpes
Adult: PO 250 mg b.i.d. for up to 1 y


  • Reduce dosage in patients with reduced kidney function.
  • Store at room temperature, 15°–30° C (59°–86° F).

Adverse Effects (≥1%)

CNS: Headache, somnolence, dizziness, paresthesias, fatigue, fever, rigors. Hematologic: Purpura. GI: Nausea, diarrhea, vomiting, constipation, anorexia, abdominal pain. Body as a Whole: Pharyngitis, sinusitis, pruritus.


Drug: Probenecid may decrease elimination; famciclovir may increase digoxin levels.


Absorption: Readily absorbed from GI tract and rapidly converted to penciclovir in intestinal and liver tissue. Onset: Median times to full crusting of lesions, loss of vesicles, loss of ulcers, and loss of crusts were 6, 5, 7, and 19 d, respectively; median time to loss of acute pain was 21 d. Peak: 1 h. Distribution: Distributes into breast milk of animals. Metabolism: Metabolized in liver and intestinal tissue to penciclovir, which is the active antiviral agent. Elimination: Approximately 60% recovered in urine as penciclovir. Half-Life: Penciclovir 2–3 h.

Nursing Implications

Assessment & Drug Effects

  • Lab tests: Baseline CBC and routine blood chemistry studies prior to and after short courses of therapy; periodically during prolonged treatment.
  • Monitor digoxin level and assess for S&S of digoxin toxicity when digoxin is used concurrently with famciclovir.

Patient & Family Education

  • Learn potential adverse effects and report those that are bothersome to physician.
  • Be aware that a full therapeutic response may take several weeks.
  • Report S&S of hypersensitivity immediately to physician.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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