A patient taking an SSRI develops agitation, muscle twitching, diaphoresis, hyperreflexia, diarrhea, and rapid heart rate after being given a single dose of tramadol for pain. The MECHANISM of this interaction is:

• A Tramadol has serotonin reuptake inhibition properties; combined with SSRI creates excess serotonergic activity (serotonin syndrome) ✓
• B Tramadol inhibits CYP2D6, increasing SSRI levels
• C Tramadol activates 5-HT3 receptors which are blocked by SSRI
• D Tramadol directly releases norepinephrine causing adrenergic toxidrome

Explanation

Tramadol has a dual mechanism: weak mu-opioid receptor agonism AND serotonin/norepinephrine reuptake inhibition (similar to SNRIs). When combined with SSRIs, both drugs increase synaptic serotonin—producing serotonin syndrome. The clinical features (altered mental status, autonomic instability, neuromuscular abnormalities including clonus/hyperreflexia) follow the Hunter Criteria for diagnosis. Tramadol is also metabolized by CYP2D6 (active metabolite O-desmethyltramadol), but SSRIs like fluoxetine/paroxetine that inhibit CYP2D6 would reduce tramadol efficacy—the primary dangerous interaction here is pharmacodynamic, not pharmacokinetic.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.