The most frequent adverse event reported during 3 clinical trials of treatment of herpes zoster (shingles) with 800 mg of oral acyclovir 5 times daily for 7 to 10 days in 323 patients was malaise (11.5%). The 323 placebo recipients reported malaise (11.1%).
The most frequent adverse event reported during 3 clinical trials of treatment of chickenpox with oral acyclovir at doses of 10 to 20 mg/kg 4 times daily for 5 to 7 days or 800 mg 4 times daily for 5 days in 495 patients was diarrhea (3.2%). The 498 patients receiving placebo reported diarrhea (2.2%).
In addition to adverse events reported from clinical trials, the following events have been identified during post-approval use of acyclovir. Because they are reported voluntarily from a population of unknown size, estimates of frequency cannot be made. These events have been chosen for inclusion due to either their seriousness, frequency of reporting, potential causal connection to acyclovir, or a combination of these factors.
General: Anaphylaxis, angioedema, fever, headache, pain, peripheral edema.
Nervous: Aggressive behavior, agitation, ataxia, coma, confusion, decreased consciousness, delirium, dizziness, dysarthria, encephalopathy, hallucinations, paresthesia, psychosis, seizure, somnolence, tremors. These symptoms may be marked, particularly in older adults or in patients with renal impairment (see PRECAUTIONS).
Digestive: Diarrhea, gastrointestinal distress, nausea.
Hematologic and Lymphatic: Anemia, leukocytoclastic vasculitis, leukopenia, lymphadenopathy, thrombocytopenia.
Hepatobiliary Tract and Pancreas: Elevated liver function tests, hepatitis, hyperbilirubinemia, jaundice.
Skin: Alopecia, erythema multiforme, photosensitive rash, pruritus, rash, Stevens-Johnson syndrome, toxic epidermal necrolysis, urticaria.
Special Senses: Visual abnormalities.
Urogenital: Renal failure, renal pain (may be associated with renal failure), elevated blood urea nitrogen, elevated creatinine, hematuria (see WARNINGS).
Overdoses involving ingestion of up to 100 capsules (20 g) have been reported. Adverse events that have been reported in association with overdosage include agitation, coma, seizures, and lethargy. Precipitation of acyclovir in renal tubules may occur when the solubility (2.5 mg/mL) is exceeded in the intratubular fluid. Overdosage has been reported following bolus injections or inappropriately high doses and in patients whose fluid and electrolyte balance were not properly monitored. This has resulted in elevated BUN and serum creatinine and subsequent renal failure. In the event of acute renal failure and anuria, the patient may benefit from hemodialysis until renal function is restored (see DOSAGE AND ADMINISTRATION).
800 mg every 4 hours orally, 5 times daily for 7 to 10 days.
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.
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.
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.
In patients with renal impairment, the dose of acyclovir tablets should be modified as shown in Table 3:
Normal Dosage Regimen
Creatinine Clearance mL/min/1.73 m 2)
Adjusted Dosage Regimen
200 mg every 4 hours
every 4 hours, 5x daily every 12 hours
400 mg every 12 hours
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
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.
No supplemental dose appears to be necessary after adjustment of the dosing interval.
Acyclovir Suspension was shown to be bioequivalent to acyclovir Capsules (n = 20) and 1 acyclovir 800-mg tablet was shown to be bioequivalent to 4 acyclovir 200-mg capsules (n = 24).
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