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Clinical Atlas Prestige · Evidence-first

Psych VivasEmergency psychiatry

Psych Vivas · Emergency psychiatry

Serotonin toxicity — structured clinical viva

Fellowship viva on Hunter criteria, linezolid trap, SS vs NMS, cyproheptadine dosing, cooling/ICU thresholds, and deprescribing.

clinical
On this page & tools

Target exams

FRANZCPMRCPsychABPNMD-DNB

Target exams

FRANZCPMRCPsychABPNMD-DNB
Prompt
You are the psychiatry registrar. ED asks you to review a 29-year-old on venlafaxine and recently started linezolid for MRSA soft-tissue infection. He has agitation, temperature 38.9 C, diaphoresis, ocular clonus, and inducible ankle clonus. A medical registrar wonders if this is NMS from an antipsychotic given two months ago. Defend your diagnosis, criteria, differential, management with doses, and prevention counselling.

Interpretation

Reveal interpretation

Diagnosis. Serotonin toxicity from venlafaxine + linezolid (linezolid has MAOI activity). Hunter pathway: serotonergic exposure plus ocular clonus with agitation and/or inducible clonus with diaphoresis/agitation — criteria met. Tempo and drug history argue strongly against delayed NMS from an antipsychotic two months ago.[1][3][4]

Differential. NMS, anticholinergic toxicity, sympathomimetic toxicity, sepsis/CNS infection, withdrawal states — use skin moisture, bowel sounds, reflex/clonus pattern, and drug timeline as discriminators.[2][4]

Management. Stop venlafaxine and reassess need/alternative for linezolid with infectious diseases. Supportive care, IV fluids, continuous monitoring, benzodiazepines (e.g. lorazepam 1–2 mg IV titrated), active cooling, cyproheptadine 12 mg oral/NG then 2 mg q2h if needed, maintenance 8 mg q6h. ICU if progressive hyperthermia/rigidity; consider non-depolarising paralysis for refractory heat generation. Avoid bromocriptine.[2][5]

Prevention counselling. Medication reconciliation before starting linezolid or methylene blue; warn about tramadol/pethidine/dextromethorphan with MAOIs; document high-risk combinations in the record; plan safer long-term antidepressant strategy after recovery.[3][5]

Escalating viva probes

ProbeModel point
Recite all Hunter rulesFive pathways including spontaneous clonus alone
Why cyproheptadine?5-HT2A antagonism; animal hyperthermia prevention support
When to paralyse?Severe hyperthermia/life-threatening rigidity refractory to cooling/benzos
Sternbach vs HunterHistorical ≥3/10 features vs preferred modern decision rules
Triptan+SSRI nuanceFDA caution vs AHS low absolute risk position

Key points

Linezolid trap

Linezolid + SNRI/SSRI can precipitate serotonin toxicity via MAOI activity.

Hunter first

Diagnose clinically with Hunter rules — no serum serotonin test.

Named regimen

Cyproheptadine 12 mg load → 2 mg q2h → maintenance 8 mg q6h (oral/NG).
[1] [2] [3]

References

  1. [1]Dunkley EJ, Isbister GK, Sibbritt D, et al. The Hunter Serotonin Toxicity Criteria: simple and accurate diagnostic decision rules for serotonin toxicity. QJM, 2003.PMID 12925718
  2. [2]Boyer EW, Shannon M The serotonin syndrome. N Engl J Med, 2005.PMID 15784664
  3. [3]Lawrence KR, Adra M, Gillman PK Serotonin toxicity associated with the use of linezolid: a review of postmarketing data. Clin Infect Dis, 2006.PMID 16652315
  4. [4]Perry PJ, Wilborn CA Serotonin syndrome vs neuroleptic malignant syndrome: a contrast of causes, diagnoses, and management. Ann Clin Psychiatry, 2012.PMID 22563571
  5. [5]Chiew AL, Isbister GK Management of serotonin syndrome (toxicity). Br J Clin Pharmacol, 2025.PMID 38926083