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Related Subjects: Acute Kidney Injury | Acute Rhabdomyolysis | Hyperkalaemia

Serotonin syndrome occurs most commonly soon after starting such medication or when the treatment dose is increased or an overdose is taken. The combination of a monoamine oxidase inhibitor (MAOI), in particular, MAO-A inhibitors that preferentially inhibit the metabolism of 5-HT, with serotonergic drugs is especially dangerous

About

• Excess serotonin (5-Hydroxytryptamine) may be due to overdose of SSRI, fluoxetine and sertraline
• Potentially life-threatening drug-induced toxidrome
• Increased serotonergic activity in peripheral (PNS) and central nervous systems (CNS).

Causes: together drugs may be additive

• Antidepressants: MAOIs, TCAs, SSRIs, SNRIs, trazodone and mirtazapine.
• Opiates: Pethidine, fentanyl, buprenorphine, oxycodone, tramadol.
• CNS stimulants: MDMA, phentermine, amphetamines, sibutramine, methamphetamine, cocaine
• Herbs: St John's Wort, ginseng, nutmeg
• Others: Valproate, buspirone, lithium, linezolid, chlorpheniramine, risperidone, olanzapine, ondansetron, granisetron, metoclopramide.

Clinical

• Inducible or ocular clonus with agitation or diaphoresis
• Tachycardia, shivering, sweating, mydriasis, diarrhoea
• Myoclonic jerks, hyperreflexia, clonus, hyperthermia.
• Increased vigilance and agitation. Metabolic acidosis
• Rhabdomyolysis. DIC, AKI, seizures.

Investigations

• FBC, U&E, LFTS, CRP, CK, lactate, Glucose, ABG
• 12 lead ECG, CXR and Urine if sepsis considered
• Unclear check CT head and LP/CSF ? HSV ? Encephalitis

Management[Get expert help early]

• ABC, Consider HDU if low GCS, High Temperature, AKI, Seizures
• Mainly supportive. Stopping serotonergic drugs usually brings about a rapid improvement.
• IV Diazepam 5-10 mg for seizures and agitation and can reduce muscle tone.
• Aggressive cooling if temperature over 40 C
• IV fluids 1-2 Litres and as needed. Supportive. Beta blockage for arrhythmias.
• Watch U&E, K, CK and Lactate and ABG for deterioration
• Consider
  • Diazepam 10mg IV. Can be repeated. Large doses may be required.
  • Cyproheptadine 12mg PO/NG stat then 8mg every 6 hours.
  • Chlorpromazine 25mg IM
  • Dantrolene 1-2.5mg/kg. Can be repeated up to a maximum of 10mg/kg.
  • Rhabdomyolysis consider 1.26% bicarbonate therapy
  • IV Glucose 10% if hypoglycaemia
• Should settle once causative drug stopped.
• Avoid opiates with intrinsic serotonergic activity

References

• Guidelines for the management of serotonin syndrome
• Serotonin Syndrome: Pathophysiology, Clinical Features, Management, and Potential Future Directions