05 December 2025
: Case report 
Time Course of Serum Dextromethorphan Concentrations in a Case of Serotonin Syndrome After Massive Overdose
Management of emergency care, Rare coexistence of disease or pathology
Seigo Yamada ABDEF 1, Hiroaki Taniguchi
ABCDEF 2, Takero Terayama ABDEF 3*, Akashi Hayakawa D 4, Hiroyuki Toda D 4, Hiroko Abe C 5, Tetsuro Kiyozumi ABDF 1
DOI: 10.12659/AJCR.949204
Am J Case Rep 2025; 26:e949204
Table 2 Summary of previously reported cases of serotonin syndrome associated with dextromethorphan.
| Authors | Patient details | Dosage | Symptoms | DXM blood concentration | Co-medication blood concentration |
|---|---|---|---|---|---|
| Schwartz et al []6 | 20-year-old man | Supra-therapeutic DXM doses | Confusion, fever (38.4°C), tachycardia (168 bpm), hyperreflexia, clonus | 950 ng/mL (on arrival) | Escitalopram 23 ng/mL, Chlorpheniramine 430 ng/mL |
| Schwartz et al []6 | 6-year-old boy | Supra-therapeutic DXM doses (40 mg/kg) | Lethargy, confusion, lower-extremity rigidity, clonus, dilated pupils, diaphoresis | 2820 ng/mL | Sertraline 12.5 ng/mL, Caffeine 1.4 μg/mL |
| Ganetsky et al []7 | 18-year-old man | Recreational use of Coricidin™ (DXM 30 mg, chlorpheniramine 4 mg per tablet) | Agitation, neuromuscular hyperactivity, and autonomic instability | 930 ng/mL | None |
| Tanaka et al []8 | 64-year-old man, peritoneal dialysis | 30 mg of DXM | Myoclonus, tremor, agitation, slurred speech, diaphoresis | 2.68 ng/mL (60 h after dose ingestion) | Metoprolol 13 ng/mL |
| Monte et al []9 | 19-year-old man | Coricidin™ up to 48 tablets (DXM up to 1440 mg, chlorpheniramine up to 192 mg) | Agitation, delirium, mydriasis, ocular clonus, autonomic instability (blood pressure, 177/113 mmHg; heart rate, 128 bpm; temperature, 38.5°C) | 250 ng/mL (12 h after dose ingestion); 38 ng/mL (38 h after dose ingestion) | Chlorpheniramine: 330 ng/mL (12 h after dose ingestion), 140 ng/mL (38 h after dose ingestion) |
| Current case | 24-year-old man | 300 mg of DXM (4.6 mg/kg) | Impaired consciousness, clonus, and autonomic instability | 398 ng/mL (13 h after dose ingestion); 26 ng/mL (day 3); 2 ng/mL (day 4); undetectable (day 5) | Trazodone below 1 ng/mL, Methylphenidate below 1 ng/mL |
| DXM – dextromethorphan; bpm – beat per minute; h – hour. | |||||