From the Guidelines
Acyclovir is an antiviral medication and does not require treatment itself, but rather is used to treat viral infections caused by herpes viruses. When considering the use of acyclovir, it's essential to understand its role in treating herpes simplex virus (HSV-1 and HSV-2), varicella-zoster virus (chickenpox and shingles), and Epstein-Barr virus. For herpes simplex infections, typical dosing is 200-800 mg orally 2-5 times daily for 5-10 days, depending on the specific condition, as per standard medical practice. However, if lesions persist in a patient receiving acyclovir treatment, resistance of the HSV strain to acyclovir should be suspected, and such patients should be managed in consultation with an expert 1. In cases of acyclovir-resistant strains, alternate therapy such as foscarnet, 40 mg/kg body weight IV every 8 hours until clinical resolution is attained, is often effective for treatment of acyclovir-resistant genital herpes 1. Key points to consider when using acyclovir include:
- Typical dosing for herpes simplex infections
- Potential for resistance and need for alternate therapy
- Importance of adequate hydration to prevent kidney problems
- Possible side effects such as nausea, headache, and dizziness It's crucial to note that all acyclovir-resistant strains are resistant to valacyclovir, and most are resistant to famciclovir, making foscarnet or topical cidofovir gel 1% applied to the lesions once daily for 5 consecutive days potential treatment options 1.
From the FDA Drug Label
OVERDOSAGE 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). The treatment for overdosage of acyclovir includes:
- Monitoring of fluid and electrolyte balance
- Hemodialysis in the event of acute renal failure and anuria, until renal function is restored 2
From the Research
Treatment Options for Acyclovir
- Acyclovir is an antiherpes agent used to treat herpes-virus infections, including those caused by herpes simplex and varicella-zoster viruses 3.
- The treatment of herpes simplex, herpes zoster, and other viral infections has been transformed by guanosine nucleoside antivirals such as valacyclovir (a prodrug of acyclovir) and famciclovir (a prodrug of penciclovir) 4.
- Valacyclovir is safe and effective in the therapy of patients with herpes simplex and herpes zoster and may be useful in other viral infections 4.
- Famciclovir and valacyclovir appear to decrease time to resolution of pain compared with acyclovir in patients with herpes zoster infections 5.
Comparison of Acyclovir with Other Antiviral Agents
- Valacyclovir is more effective than acyclovir and equally effective as famciclovir at hastening the healing of zoster-associated pain and postherpetic neuralgia (PHN) 4.
- A randomized clinical trial found that famciclovir is non-inferior to acyclovir in the treatment of herpes zoster, with similar rates of cure and time to full crusting of lesions 6.
- The discovery of acyclovir and penciclovir has led to the development of a successful systemic therapy for treating herpes simplex virus infection and varicella-zoster virus infection 7.
Mechanism of Action and Resistance
- Acyclovir and penciclovir are phosphorylated by viral thymidine kinase and are incorporated into the DNA chain by viral DNA polymerase, resulting in chain termination 7.
- Helicase-primase inhibitors (HPIs) such as pritelivir and amenamevir have novel mechanisms of action, drug resistance properties, pharmacokinetic characteristics, and clinical efficacy for treating genital herpes and herpes zoster 7.