21/08/2025
Drug-Induced Serotonin Syndrome:
A Neurologic Emergency
Key Points
1. Definition: A potentially life-threatening condition caused by excessive serotonergic activity in the CNS and peripheral nervous system.
2. Mechanism: Overstimulation of 5-HT1A/2A receptors due to:
◦ Increased serotonin synthesis (e.g., tryptophan)
◦ Decreased serotonin breakdown (MAOIs)
◦ Increased serotonin release (amphetamines, M**A)
◦ Direct receptor agonism (triptans, L*D)
◦ Reuptake inhibition (SSRIs, SNRIs, TCAs)
High-Risk Medications
1. Common Culprits
• Antidepressants: SSRIs (fluoxetine), SNRIs (venlafaxine), TCAs (clomipramine), MAOIs (phenelzine)
• Opioids: Tramadol, fentanyl, meperidine (pethidine)
• Migraine drugs: Triptans (sumatriptan)
• Antiemetics: Ondansetron, metoclopramide
• Recreational drugs: M**A, co***ne, L*D
2. Dangerous Combinations
• SSRI + MAOI (e.g., fluoxetine + linezolid) → absolute contraindication
• SSRI + tramadol (common in pain patients)
• SNRI + dextromethorphan (cough syrup)
Clinical Presentation
Hunter Criteria (Diagnosis Requires ≥1 of These)
• Spontaneous clonus (most specific sign)
• Inducible clonus + agitation/diaphoresis
• Ocular clonus + agitation/diaphoresis
• Hypertonia + hyperthermia (>38°C)
• Tremor + hyperreflexia
Triad of Symptoms
1. Neuromuscular: Myoclonus, hyperreflexia, rigidity
2. Autonomic: Tachycardia, hypertension, hyperthermia
3. Mental status changes: Agitation, delirium, coma
Management
1. Immediate Actions
◦ Discontinue all serotonergic drugs
◦ Supportive care: IV fluids, cooling for hyperthermia
◦ Benzodiazepines (e.g., lorazepam) for agitation/seizures
2. Severe Cases (Hyperthermia >41°C, Rigidity)
◦ Cyproheptadine (5-HT2A antagonist): 12 mg PO/NG, then 2–8 mg q6h
◦ ICU admission for intubation, paralysis, and cooling
3. Avoid
◦ Dantrolene (not effective; unlike malignant hyperthermia)
◦ Antipsychotics (may worsen hyperthermia)
Prevention
• Washout periods:
◦ 2 weeks between MAOIs and SSRIs
◦ 5 weeks for fluoxetine (long half-life)
• Check for drug interactions (e.g., St. John’s wort + SSRI)
Take-Home Message
• Suspect serotonin syndrome in any patient on serotonergic drugs with altered mental status + neuromuscular hyperactivity.
• Clonus + hyperreflexia are hallmark signs.
• When in doubt, stop the drugs and monitor.
Mnemonic: "SEROTONIN"
• Sweating
• Encephalopathy
• Rigidity
• Ocular clonus
• Tremor
• Overactive reflexes
• Nausea/vomiting
• Inducible clonus
• Neuromuscular excitation