Relative safety of mirtazapine overdose

A 43-y-o male with a history of AIDS, atrial fibrillation, and alcohol abuse presented to the emergency department 2 h after ingestion of 25 tablets of 15 mg mirtazapine (total 375 mg) with ethanol in a suicide attempt (no other coingestion). Vital signs were normal except for a mild tachycardia (rate 112). Physical examination was unremarkable except for lethargy. Fifty grams of activated charcoal with sorbitol was given. Electrocardiogram showed sinus tachycardia, left ventricular hypertrophy, and non-specific ST-segment changes. Serum mirtazapine on admission was 530 ng/mL (therapeutic level 20-50 ng/mL). Overnight monitoring revealed no tachyarrythmias, and discharge occurred after psychiatric evaluation. It appears that ingestions of mirtazapine approximately 10-fold of therapeutic exhibit minimal acute toxicity. From this and other cases in the literature exhibiting a 10-fold overdose, we conclude that isolated mirtazapine ingestions of this magnitude require no acute intervention other than short term (about 6 h) observation.