Which drug is safe to use when taking erythromycin, considering potential drug interactions?

Erythromycin is an antibiotic that can significantly affect the metabolism of various drugs due to its inhibition of the cytochrome P450 system, particularly CYP3A4. This interaction can lead to increased plasma levels of other medications that are metabolized by the same pathway, potentially causing toxicity.

Furosemide, a loop diuretic, is not primarily metabolized by CYP3A4 and therefore is considered safe to use concomitantly with erythromycin. It works by a different mechanism, primarily by inhibiting sodium and chloride reabsorption in the ascending loop of Henle, leading to diuresis without the risk of serious drug interactions with erythromycin.

In contrast, the other listed medications pose significant risks when taken with erythromycin. Theophylline, for example, can have its clearance decreased, leading to increased plasma concentrations and potential toxicity. Warfarin has an increased risk of bleeding due to altered metabolism, and diazepam could result in elevated blood levels, increasing the risk of sedation and respiratory depression.

Therefore, furosemide stands out as the safest option among these drugs for co-administration with erythromycin, minimizing the risk of adverse effects.