A 32-year-old woman with major depressive disorder has been on sertraline 100 mg daily for 3 months with good response. She presents to the emergency department with a 6-hour history of agitation, confusion, and tremor. On examination: temperature 38.8°C, heart rate 118/min, blood pressure 148/92 mmHg, hyperreflexia, and clonus in the lower limbs. She denies recent medication changes but admits to self-starting fluoxetine 20 mg daily 2 days ago for "faster relief." Creatine kinase is 1200 U/L (normal <200). What is the most appropriate immediate management?

Explanation

## Diagnosis: Serotonin Syndrome **Key Point:** This patient has classic serotonin syndrome triggered by concurrent use of two SSRIs (sertraline + fluoxetine), creating excessive serotonergic activity. ### Clinical Features Present - **Triad of serotonin syndrome:** 1. Autonomic instability (fever 38.8°C, tachycardia, hypertension) 2. Neuromuscular abnormalities (tremor, hyperreflexia, clonus) 3. Altered mental status (agitation, confusion) - **Timeline:** Acute onset (6 hours) after adding second SSRI - **Elevated CK:** Indicates muscle involvement (rhabdomyolysis risk) ### Management Algorithm ```mermaid flowchart TD A[Serotonin Syndrome Suspected]:::outcome --> B{Severity?}:::decision B -->|Mild: tremor, hyperreflexia only| C[Discontinue serotonergic agent]:::action B -->|Moderate: clonus + autonomic changes| D[Stop all serotonergics immediately]:::action B -->|Severe: temp >40°C, rhabdo, DIC| E[ICU admission]:::urgent C --> F[Supportive care, monitor]:::action D --> G[Benzodiazepines for agitation/seizures]:::action D --> H[Active cooling if hyperthermic]:::action D --> I[IV fluids, monitor CK/renal function]:::action E --> J[All measures + consider cyproheptadine]:::action G --> K[Resolution in 24-72 hours]:::outcome ``` ### Immediate Management Steps 1. **Discontinue both SSRIs** — no washout period needed; serotonin syndrome resolves within 24–72 hours of cessation 2. **Benzodiazepines** (lorazepam 2–4 mg IV/IM) — first-line for agitation and seizure prophylaxis 3. **Supportive care** — active cooling, IV fluids, continuous monitoring of vital signs and CK 4. **Avoid cyproheptadine in mild-to-moderate cases** — reserved for severe, refractory serotonin syndrome; not first-line **High-Yield:** Serotonin syndrome is a **clinical diagnosis**; no specific lab confirms it. Diagnosis relies on symptom triad + temporal relationship to serotonergic drug exposure. **Clinical Pearl:** Unlike neuroleptic malignant syndrome (NMS), serotonin syndrome has **rapid onset** (hours to days), **rapid resolution** (24–72 hours after drug discontinuation), and **clonus is pathognomonic** for serotonin syndrome. ### Why NOT Cyproheptadine? - Cyproheptadine (5-HT~1A~ and 5-HT~2A~ antagonist) is a **second-line agent** used only in severe, life-threatening serotonin syndrome unresponsive to benzodiazepines - Not indicated as first-line; supportive care + benzodiazepines are sufficient for this moderate case - Onset of action is slow (30–60 min); benzodiazepines work faster [cite:Harrison 21e Ch 385]