Synopsis
Recognise clonus-based serotonin toxicity, reconstruct interacting exposures, stop serotonergic drugs, and control agitation, hyperthermia and organ injury without confusing it with neuroleptic malignant syndrome.
- Serotonin syndrome is a predictable toxicity from excessive serotonergic activity, most often after combination, overdose, dose escalation or a pharmacokinetic interaction rather than an idiosyncratic allergy.
- Symptoms usually begin within hours of a new exposure and combine mental-state change, autonomic activation and neuromuscular hyperactivity.
- Spontaneous, inducible or ocular clonus is the most discriminating bedside sign; hyperreflexia and tremor are often more prominent in the legs.
Key red flags
Temperature above 40 degrees, sustained rigidity, seizure, acidosis or rapidly rising CK indicates life-threatening toxicity requiring intubation and paralysis.
Investigation priorities
Identify serotonergic combinations, overdose, long half-life and metabolic interaction.
Management branches
Agitation, sweating and abnormal movements follow a medicine change or overdose.
- Stop all serotonergic and non-essential psychoactive medicines, secure an accurate exposure history and contact the National Poisons Information Service.
- Examine pupils, skin, bowel sounds, reflexes and spontaneous, ocular and inducible clonus while measuring core temperature and cardiorespiratory stability.
Key medicines
Lorazepam or diazepamTitrate intravenous or oral benzodiazepine in small repeated doses using current BNF and toxicology advice, with continuous respiratory observation in severe illness.
CyproheptadineToxicology may recommend an initial enteral dose followed by repeat and maintenance doses from current TOXBASE guidance; it cannot be given intravenously.