A 45-year-old client takes duloxetine 60 mg daily for diabetic peripheral neuropathy and is now prescribed sumatriptan for new migraines, plus an over-the-counter cold remedy containing dextromethorphan. Which adverse outcome does the nurse counsel the client to recognize?

Duloxetine (Cymbalta) is a serotonin-norepinephrine reuptake inhibitor (SNRI) and a first-line agent for diabetic peripheral neuropathy, fibromyalgia, chronic musculoskeletal pain, major depression, and generalized anxiety disorder. Combining duloxetine with other serotonergic agents — triptans (sumatriptan, rizatriptan), other SSRIs/SNRIs, MAOIs, tramadol, dextromethorphan, ondansetron, linezolid, methylene blue, St John wort, or recreational drugs like MDMA — increases the risk of serotonin syndrome. Clinical features include mental status changes, neuromuscular hyperactivity (hyperreflexia, clonus including ocular clonus, tremor, rigidity), and autonomic instability (hyperthermia, tachycardia, hypertension, diaphoresis, mydriasis, GI symptoms). Onset is often within hours and severity ranges from mild to lethal. Management: stop all serotonergic agents, supportive care including IV fluids and cooling, benzodiazepines for agitation, and in severe cases cyproheptadine. Other duloxetine teaching: gradual taper at discontinuation to avoid SNRI discontinuation syndrome, suicidal ideation FDA boxed warning especially under age 25, hepatic concern with alcohol, BP and heart rate monitoring, do not crush or chew capsules, take consistently. Dental, anemia, and hearing loss are not the priority risks here.

Duloxetine + triptan + dextromethorphan = stacked serotonergic risk. Hyperreflexia with clonus is the hallmark exam finding for serotonin syndrome.