Family Nurse Practitioner Exam

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

1. Theophylline (Theo-Dur)

2. Warfarin (Coumadin)

3. Diazepam (Valium)

4. Furosemide (Lasix)

The correct answer is: Furosemide (Lasix)

Erythromycin is a macrolide antibiotic that is known to interact with several medications through its effect on cytochrome P450 enzymes, particularly CYP3A4. This can lead to increased plasma concentrations of drugs that are metabolized by this enzyme, thereby increasing the risk of side effects or toxicity. Furosemide, a loop diuretic, is not significantly affected by erythromycin in terms of drug interactions. It is primarily eliminated by the renal system and does not undergo significant metabolism via the cytochrome P450 pathway. Therefore, it is considered safe to use in conjunction with erythromycin, as it is unlikely to experience any altered pharmacokinetics due to the presence of the antibiotic. In contrast, other medications such as theophylline, warfarin, and diazepam are all substrates of the cytochrome P450 enzyme system. Theophylline can have increased levels when taken with erythromycin, leading to toxicity. Warfarin's anticoagulant effects can be potentiated, risking bleeding complications. Similarly, diazepam may have increased sedative effects due to elevated concentrations. Thus, furosemide emerges as the safest option to use alongside erythromycin without concerning interactions.