A nurse is collecting data from a client who takes several daily medications and states that he wants to ask the provider for a prescription for sildenafil. The nurse knows that sildenafil is contraindicated due to an interaction with which of the following client's medications?

A. There's no documented interaction between cefuroxime and sildenafil. Cefuroxime is an antibiotic, and there are no known significant interactions with sildenafil. B. There's no documented interaction between metformin and sildenafil. Metformin, an antidiabetic medication, does not interact significantly with sildenafil. C. Both sildenafil and isosorbide are vasodilators, and concomitant use can result in severe hypotension due to additive effects on blood pressure lowering. Therefore, their combination is contraindicated. D. Naproxen, a nonsteroidal anti-inflammatory drug (NSAID), does not have a significant interaction with sildenafil. They can be safely used together in most cases, although caution may be needed in individuals with cardiovascular risk factors.