What it's for (Indications)
- Acyclovir is an antiviral nucleoside analog indicated for the treatment of infections caused by herpes simplex virus (HSV) types 1 and 2, and varicella-zoster virus (VZV).
- Specific indications include the treatment of initial genital herpes and the management of recurrent episodes, including suppression.
- It is also used for the acute treatment of herpes zoster (shingles) and the treatment of varicella (chickenpox).
- Furthermore, acyclovir is indicated for the prophylaxis of recurrent genital herpes in immunocompetent individuals and for the treatment of mucocutaneous herpes simplex infections in immunocompromised patients.
- The intravenous formulation is reserved for severe infections, such as encephalitis, neonatal herpes, and severe mucocutaneous HSV infections in immunocompromised patients, or other serious HSV/VZV infections requiring systemic therapy.
Dosage Information
| Type | Guideline |
|---|---|
| Standard | Acyclovir dosage varies significantly depending on the specific viral infection, patient age, renal function, and immune status. It is available in oral (tablets, capsules, suspension), intravenous, and topical formulations. For oral administration, typical doses range from 200 mg five times a day for initial genital herpes to 800 mg five times a day for herpes zoster, usually for a duration of 5 to 10 days. Prophylactic regimens for recurrent genital herpes might involve 400 mg twice daily. Intravenous dosing is based on body weight (e.g., 5-10 mg/kg infused over 1 hour, every 8 hours) and requires careful adjustment in patients with impaired renal function. Topical formulations are applied to affected areas usually five times daily. Accurate dosing requires careful evaluation of the patient's clinical condition and adherence to prescribing information to ensure therapeutic efficacy and minimize adverse effects, particularly concerning renal impairment. |
Safety & Warnings
Common Side Effects
- Common adverse effects associated with acyclovir, particularly oral administration, include nausea, vomiting, diarrhea, and headache.
- Other frequently reported side effects may involve malaise, abdominal pain, and skin rash.
- More serious, albeit less common, adverse reactions can occur, especially with intravenous administration or in patients with compromised renal function or advanced age.
- These include renal dysfunction, characterized by elevated serum creatinine and blood urea nitrogen, which can lead to acute renal failure if not managed appropriately.
- Neurological effects such as lethargy, confusion, hallucinations, tremors, seizures, and coma have been reported, primarily in patients with renal impairment, the elderly, or those receiving high doses.
- Anaphylaxis, angioedema, hepatitis, and hematological abnormalities (e.
- g.
- , thrombocytopenia, leukopenia) are rare but serious adverse events that require immediate medical attention.
Serious Warnings
- Black Box Warning: **Serious Warnings** Acyclovir does not carry an FDA-mandated Black Box Warning. However, healthcare professionals and patients should be aware of several serious potential risks. **Renal Impairment:** Acute renal failure, sometimes fatal, has been observed, particularly with intravenous acyclovir, in patients who are dehydrated, have pre-existing renal disease, or are receiving concomitant nephrotoxic agents. Adequate hydration is paramount during intravenous administration, and dosage adjustment is imperative in patients with impaired renal function to minimize the risk of renal tubular damage and crystalluria. Renal function should be closely monitored throughout therapy, especially with higher doses or prolonged treatment. **Neurological Adverse Events:** Neurological effects, including lethargy, confusion, hallucinations, tremors, seizures, and coma, have been reported, primarily in older adults and patients with renal impairment who receive high doses or accumulate the drug due to decreased renal clearance. These effects can be severe and require careful patient monitoring, particularly in vulnerable populations. Discontinuation of the drug and supportive care may be necessary if such symptoms develop. **Drug Resistance:** Prolonged or repeated courses of acyclovir, particularly in immunocompromised patients, may lead to the selection of drug-resistant strains of HSV or VZV, potentially resulting in treatment failure. Clinical response should be monitored, and if a lack of response is observed, resistance testing may be considered.
- Patients receiving acyclovir, particularly intravenous formulations or those with underlying renal impairment, must maintain adequate hydration to prevent renal crystalluria and subsequent renal toxicity.
- Dosage adjustment is crucial in patients with renal dysfunction to avoid drug accumulation and increased risk of adverse effects, including neurological complications.
- Acyclovir is generally not curative for herpes infections; it manages symptoms and reduces viral shedding.
- Patients should be advised that acyclovir does not prevent the transmission of herpes simplex virus to others, and precautions such as avoiding intercourse during outbreaks and using barrier methods should still be practiced.
- Resistance to acyclovir can develop, especially in immunocompromised patients with prolonged or repeated exposure, leading to treatment failure.
- Therefore, careful monitoring of clinical response is essential, and alternative therapies may be required if resistance is suspected.
How it Works (Mechanism of Action)
Acyclovir is a synthetic purine nucleoside analogue with in vitro and in vivo inhibitory activity against herpes simplex virus types 1 (HSV-1), type 2 (HSV-2), and varicella-zoster virus (VZV). Its antiviral action is highly selective due to its unique mechanism. Acyclovir is initially phosphorylated to its active triphosphate form (acyclovir triphosphate) predominantly by the viral thymidine kinase, an enzyme present in herpesvirus-infected cells but absent or at very low levels in uninfected cells. This selective phosphorylation leads to high concentrations of the active drug within infected cells. Acyclovir triphosphate then competitively inhibits viral DNA polymerase, preventing the elongation of the viral DNA chain and acting as a DNA chain terminator by being incorporated into the viral DNA. This leads to irreversible inactivation of the viral DNA polymerase, effectively halting viral replication without significantly affecting host cell DNA synthesis.