A 42-year-old woman with major depressive disorder has been on sertraline 100 mg daily for 3 weeks. She now presents with complaints of severe headache, muscle rigidity, hyperthermia (38.5°C), and altered mental status. Her husband reports she started taking a herbal supplement (St. John's Wort) 2 days ago for "additional energy." On examination, she has hyperreflexia and clonus. What is the most appropriate immediate management?

Explanation

## Clinical Diagnosis: Serotonin Syndrome ### Pathophysiology The patient presents with classic serotonin syndrome — a potentially life-threatening condition caused by excessive serotonergic activity. St. John's Wort is a potent CYP3A4 and CYP2C9 inducer that also has intrinsic SSRI-like activity. Combined with sertraline, it creates a synergistic serotonergic overload. ### Clinical Triad of Serotonin Syndrome 1. **Neuromuscular** — hyperreflexia, clonus, muscle rigidity, tremor 2. **Autonomic** — hyperthermia, tachycardia, hypertension, diaphoresis 3. **Mental status** — agitation, confusion, altered consciousness ### Immediate Management Algorithm ```mermaid flowchart TD A[Suspected Serotonin Syndrome]:::outcome --> B{Severity?}:::decision B -->|Mild-Moderate| C[Discontinue serotonergic agents]:::action B -->|Severe with hyperthermia| D[Discontinue immediately]:::action C --> E[Supportive care, observe]:::action D --> F[Aggressive cooling measures]:::action D --> G[ICU monitoring]:::action F --> H[IV fluids, benzodiazepines]:::action H --> I[Consider cyproheptadine if severe]:::action I --> J[Serotonin syndrome resolves]:::outcome ``` ### Key Point: **Immediate discontinuation of ALL serotonergic agents is the cornerstone of management.** Continuing either medication risks progression to malignant hyperthermia-like state with rhabdomyolysis and acute kidney injury. ### High-Yield: Serotonin syndrome typically develops within **hours to days** of dose increase or drug combination. St. John's Wort is a major culprit — it is NOT a benign supplement and interacts with SSRIs, SNRIs, TCAs, MAOIs, and tramadol. ### Clinical Pearl: Unlike neuroleptic malignant syndrome (NMS), serotonin syndrome: - Develops **rapidly** (hours to 1–2 days) - Resolves **rapidly** (24–72 hours) after drug discontinuation - Features **hyperreflexia and clonus** (NMS has hyporeflexia) - Does NOT require dantrolene (supportive care + benzodiazepines suffice) ### Supportive Care Measures - **Cooling:** ice packs, cool IV fluids, cooling blankets - **Benzodiazepines:** lorazepam or diazepam for agitation and muscle relaxation - **Hydration:** IV fluids to prevent rhabdomyolysis-induced acute kidney injury - **Monitoring:** core temperature, CK, electrolytes, urine myoglobin ### Cyproheptadine Role Cyproheptadine (a 5-HT~1A~ and 5-HT~2A~ antagonist) is reserved for **severe, refractory cases** and is given as a loading dose (12 mg) followed by 2 mg every 2 hours. It is NOT first-line; discontinuation + supportive care resolves most cases.