A nurse reviews the medication list of an organ transplant recipient taking cyclosporine. Which additional prescribed medication should cause the most concern?

A. Nystatin is an antifungal that is minimally absorbed systemically when taken orally. It is generally safe to use in transplant recipients and does not significantly interact with cyclosporine. Therefore, it is not a major concern. B. A standard multivitamin does not have significant drug interactions with cyclosporine. While it is important to monitor nutrient intake in transplant recipients, multivitamins are not considered a serious interaction risk. C. Clarithromycin is a macrolide antibiotic that inhibits cytochrome P450 3A4, the enzyme responsible for metabolizing cyclosporine. Co-administration can significantly increase cyclosporine blood levels, leading to toxicity. Cyclosporine toxicity can cause nephrotoxicity, hypertension, neurotoxicity, and increased risk of infections, making this combination potentially dangerous. Clients taking both medications require close monitoring, dose adjustments, or alternative therapy. D. Fluconazole is an antifungal that can also inhibit CYP3A4 and may increase cyclosporine levels, but the effect is generally less pronounced than with clarithromycin. Although monitoring is still important, clarithromycin poses a higher immediate risk for toxicity in this scenario.