💊 Aciclovir

Aciclovir is an antiviral drug, specifically a synthetic purine nucleoside analogue. It is primarily used to treat infections caused by herpes simplex virus (HSV) and varicella-zoster virus (VZV).

Aciclovir is a prodrug that is selectively phosphorylated by viral thymidine kinase in infected cells, converting it into aciclovir monophosphate. Host cell kinases then convert it to aciclovir triphosphate, which competitively inhibits viral DNA polymerase and is incorporated into viral DNA, leading to chain termination.

Aciclovir is indicated for the treatment of herpes simplex infections of the skin and mucous membranes, including initial and recurrent genital herpes. It is also used for the treatment of herpes zoster (shingles) and varicella (chickenpox). Prophylaxis of HSV infections in immunocompromised patients is another key indication.

Known hypersensitivity to aciclovir or valaciclovir is an absolute contraindication. Caution is required in patients with renal impairment, as dose adjustments are necessary to prevent accumulation and toxicity. Dehydration should be avoided, especially during intravenous administration.

Common adverse effects include headache, dizziness, nausea, vomiting, diarrhoea, and abdominal pain. Skin rashes and photosensitivity can also occur. Rarely, neurological effects such as confusion, hallucinations, and seizures have been reported, particularly with high doses or in renally impaired patients. Renal dysfunction can occur, especially with rapid intravenous infusion.

Renal function should be monitored, especially in elderly patients, those with pre-existing renal impairment, or during intravenous administration. Adequate hydration should be ensured, particularly with IV use. Monitor for neurological symptoms, especially in susceptible individuals.

Always check for known allergies to aciclovir or valaciclovir. Be aware of potential drug interactions, such as with probenecid which can increase aciclovir levels. For intravenous administration, ensure adequate hydration and slow infusion to prevent renal toxicity. Counsel patients on the importance of hydration and to report any unusual side effects.

High-yield facts include its selective activation by viral thymidine kinase and its efficacy against HSV and VZV. Remember its use in immunocompromised patients for prophylaxis. Emphasise the importance of early treatment for shingles to reduce post-herpetic neuralgia. Renal dose adjustment is a critical safety point.

SBA questions often test the appropriate use of aciclovir for different herpes infections, such as differentiating treatment for primary vs. recurrent genital herpes or the timing for shingles treatment. Questions may also focus on dose adjustments in renal impairment or identifying adverse effects related to renal or neurological toxicity. The prodrug mechanism and viral selectivity are also common themes.