Switch fluoxetine to bupropion, since sexual dysfunction is a well-known SSRI side effect and bupropion has the lowest rate of sexual side effects among antidepressants.

Reflexively switching antidepressants without assessing the etiology risks destabilizing a 3-year remission for a symptom that may not be medication-related.

Assess the temporal relationship between the erectile dysfunction and the SSRI, and screen for medical and psychosocial causes before attributing it to fluoxetine.

Sexual dysfunction has multiple potential etiologies: medication-related (SSRI, antihypertensives, other medications), medical (diabetes, cardiovascular disease, hypogonadism, hyperprolactinemia), psychological (performance anxiety, relationship issues), and age-related vascular changes. The temporal relationship is important — if the dysfunction began 3 years ago when fluoxetine started, the SSRI is more likely contributory. If it developed recently while on a stable dose, medical causes become more likely. A comprehensive assessment prevents unnecessary medication changes.

Add sildenafil to address the erectile dysfunction while continuing fluoxetine unchanged, since this preserves the stable antidepressant regimen while targeting the specific sexual complaint.

Adding sildenafil without assessment assumes the etiology and misses potentially significant medical conditions.

Reassure the patient that erectile changes are a normal and expected part of aging at 50 and do not require further medical workup or medication adjustment at this time.

Dismissing the symptom as age-related without assessment fails the patient. Erectile dysfunction in a 50-year-old can be an early marker of cardiovascular disease.