Acyclovir

Drug Interactions: See CLINICAL PHARMACOLOGY: Pharmacokinetics .

Acyclovir tablets are indicated for: - Acute treatment of herpes zoster (shingles) - Treatment of initial episodes and management of recurrent episodes of genital herpes - Treatment of chickenpox (varicella). The label notes effectiveness is greatest when therapy is started early after symptom onset.

Acute Treatment of Herpes Zoster: 800 mg every 4 hours orally, 5 times daily for 7 to 10 days. Genital Herpes: Treatment of Initial Genital Herpes: 200 mg every 4 hours, 5 times daily for 10 days. Chronic Suppressive Therapy for Recurrent Disease: 400 mg 2 times daily for up to 12 months, followed by re-evaluation. Alternative regimens have included doses ranging from 200 mg 3 times daily to 200 mg 5 times daily. The frequency and severity of episodes of untreated genital herpes may change over time. After 1 year of therapy, the frequency and severity of the patient’s genital herpes infection should be re-evaluated to assess the need for continuation of therapy with acyclovir tablets. Intermittent Therapy: 200 mg every 4 hours, 5 times daily for 5 days. Therapy should be initiated at the earliest sign or symptom (prodrome) of recurrence. Treatment of Chickenpox: Children (2 years of age and older): 20 mg/kg per dose orally 4 times daily (80 mg/kg/day) for 5 days. Children over 40 kg should receive the adult dose for chickenpox. Adults and Children over 40 kg: 800 mg 4 times daily for 5 days. Intravenous acyclovir is indicated for the treatment of varicella-zoster infections in immunocompromised patients. When therapy is indicated, it should be initiated at the earliest sign or symptom of chickenpox. There is no information about the efficacy of therapy initiated more than 24 hours after onset of signs and symptoms. Patients With Acute or Chronic Renal Impairment: In patients with renal impairment, the dose of acyclovir tablets should be modified as shown in Table 3. Table 3. Dosage Modification for Renal Impairment Normal Dosage Regimen Creatinine Clearance (mL/min/1.73 m 2) Adjusted Dosage Regimen Dose (mg) Dosing Interval 200 mg every 4 hours > 10 0-10 200 200 every 4 hours, 5x daily every 12 hours 400 mg every 12 hours > 10 0-10 400 200 every 12 hours every 12 hours 800 mg every 4 hours > 25 10-25 0-10 800 800 800 every 4 hours, 5x daily every 8 hours every 12 hours Hemodialysis: For patients who require hemodialysis, the mean plasma half-life of acyclovir during hemodialysis is approximately 5 hours. This results in a 60% decrease in plasma concentrations following a 6-hour dialysis period. Therefore, the patient’s dosing schedule should be adjusted so that an additional dose is administered after each dialysis. Peritoneal Dialysis: No supplemental dose appears to be necessary after adjustment of the dosing interval.

In controlled trials, the most frequent reactions were malaise (about 11.5%), nausea/vomiting (2.7%), and diarrhea (2.4%). Serious post-approval adverse events reported include CNS effects such as "aggressive behavior, agitation, ataxia, coma, confusion, decreased consciousness, delirium, dizziness," and renal/urogenital complications including "renal failure, renal pain," sometimes associated with crystalluria.