Serotonin syndrome

Serotonin syndrome results from the overstimulation of 5HT-1A receptors. 

The classical triad of serotonin syndrome is: 

• Neuromuscular abnormality
• Tremor 
• Hyperflexia 
• Clonus 
• Hypertonia 
• Autonomic hyperactivity 
• Hyperthermia 
• Hyperhidrosis 
• Tachycardia 
• Diarrhoea 
• Mydriasis 
• Hyper or hypo tension 
• Mental state changes 
• Confusion 
• Coma 
• Agitation 
• Elevated mood 

Onset of symptoms is rapid, within 24 hrs of starting drug or of overdose

Drugs which can contribute to serotonin syndrome include: 

• Antidepressants/mood stabilisers 
• SSRIs
• TCA 
• MAOI 
• SNRIs 
• Lithium 
• St John’s Wort 
• Analgesics
• Fentanyl
• Tramadol 
• Illegal drugs 
• Cocaine 
• Ecstasy 
• Amphetamines 
• Others 
• Carbamazepine 
• Triptans 
• Linezolid 

Note that serotonin syndrome may be precipitated by a person who is taking a stable dose of an SSRI taking any medication which is a P450 inhibitor. 

Treatment of serotonin syndrome is: 

• Discontinue cause 
• Supportive management 
• Cyproheptadine – a histamine-1 and 5HT2 receptor antagonist 
• Chlorpromazine may have a role but is not widely used due to risk of adverse effects 

References

Ables, A. and Nagubilli, R. Prevention, recognition, and management of serotonin syndrome. Am Fam Physician. 2010; 81(9): 1139-1142. 

Birmes, P. et al. Serotonin syndrome: a brief review. CMAJ. 2003; 168(11): 1439-1442.