A 32-year-old woman on fluoxetine for depression is started on tramadol for chronic back pain. She presents to the emergency department with agitation, tremor, hyperreflexia, and a core temperature of 38.5°C. What is the drug of choice for acute management of serotonin syndrome in this patient?

Explanation

## Management of Serotonin Syndrome **Key Point:** Cyproheptadine is the specific pharmacological antidote for serotonin syndrome. It is a non-selective 5-HT antagonist that blocks both 5-HT~1A~ and 5-HT~2A~ receptors, directly counteracting excess serotonergic activity. ## Mechanism of Action Cyproheptadine works through: 1. Antagonism of central and peripheral 5-HT receptors 2. Rapid onset of action (within 12 hours of symptom resolution in most cases) 3. Both antiserotonergic and antihistaminic properties ## Dosing and Administration **High-Yield:** Standard regimen is: - **Loading dose:** 12 mg orally or via nasogastric tube - **Maintenance:** 2 mg every 2 hours (or 4–8 mg every 6 hours) until symptom resolution - **Maximum:** Typically 32 mg/day ## Supportive Measures While cyproheptadine is the specific agent, comprehensive management includes: - **Immediate:** Discontinue all serotonergic agents (SSRI, tramadol, MAOIs, etc.) - **Symptomatic control:** Benzodiazepines (lorazepam) for agitation and muscle rigidity - **Cooling measures:** For hyperthermia (ice packs, cooling blankets) - **Monitoring:** Vital signs, core temperature, CK levels (rhabdomyolysis risk) ## Differential: Serotonin Syndrome vs. Neuroleptic Malignant Syndrome | Feature | Serotonin Syndrome | NMS | |---------|-------------------|-----| | **Onset** | Hours to days | Days to weeks | | **Causative agents** | SSRIs, tramadol, MAOIs, linezolid | Antipsychotics (D~2~ antagonists) | | **Specific treatment** | Cyproheptadine | Dantrolene + bromocriptine | | **Hyperreflexia** | Prominent | May be absent | | **GI symptoms** | Common (diarrhea) | Rare | | **Mydriasis** | Often present | Absent | **Clinical Pearl:** The presence of **diarrhea and hyperreflexia** strongly favors serotonin syndrome over NMS, making cyproheptadine the correct choice in this case. **Warning:** Do NOT confuse serotonin syndrome with NMS — they require different specific pharmacological agents (cyproheptadine vs. dantrolene). ## Why Cyproheptadine Is First-Line 1. **Direct antagonism** of serotonergic excess (not just symptomatic relief) 2. **Rapid symptom resolution** when given early 3. **Oral bioavailability** (can be given via NG tube if needed) 4. **No risk of worsening** the underlying condition (unlike propranolol, which may mask compensatory tachycardia) [cite:Harrison 21e Ch 459]