Which medication must be monitored closely for renal function due to its nephrotoxicity?

Acyclovir is an antiviral medication commonly used to treat infections caused by certain viruses, including herpes simplex and varicella-zoster. One important aspect of acyclovir is its potential nephrotoxicity, which can occur, especially when it is administered rapidly through intravenous (IV) infusion or in patients with pre-existing renal impairment.

The mechanism behind the nephrotoxicity associated with acyclovir involves the crystallization of the drug in the renal tubules, which can lead to acute kidney injury if adequate hydration is not maintained. This crystallization can obstruct the renal tubules, increasing the pressure within the kidneys and impairing their ability to filter blood effectively. As a result, it is critical to monitor renal function closely in patients receiving acyclovir, particularly because adjustments in dosage may be required for individuals with varying levels of renal function.

In contrast, while metformin can pose risks related to renal function, especially concerning lactic acidosis in patients with significant renal impairment, its primary mechanism of toxicity is different and does not lead to nephrotoxicity in the same acute way as acyclovir. Amoxicillin, an antibiotic, has a relatively wide therapeutic index, and although monitoring may be warranted in patients with renal insufficiency, it