A nurse is providing medication teaching about sildenafil to a client who has erectile dysfunction. Which of the following statements is the nurses highest priority?

A. "This medication does not prevent sexually transmitted infections.": While it is important for clients to understand that sildenafil does not provide protection against STIs, this information is educational rather than immediately safety-related. It is important but not the highest priority. B. "Take the medication before you plan to engage in sexual intercourse.": Proper timing of sildenafil is necessary for efficacy, but incorrect timing does not pose an immediate life-threatening risk. This instruction focuses on therapeutic effectiveness rather than urgent safety. C. "This medication can cause a headache.": Headache is a common side effect due to vasodilation, but it is generally mild and self-limiting. Although clients should be aware, it is not a priority safety concern. D. "If you have an erection for more than four hours, seek emergency treatment.": Priapism is a rare but serious adverse effect of sildenafil that can cause permanent tissue damage and erectile dysfunction if not treated promptly. Educating the client about this risk is the highest priority because it involves immediate, potentially irreversible harm.