OBJECTIVE: The cytochrome P450 2D6 (CYP2D6) is an enzyme involved in the oxidative biotransformation of various widely used drugs, including paroxetine, a substrate and strong inhibitor of the enzyme. The aim is to report on a case of protracted intoxication with paroxetine after a single overdose in a genotype-predicted intermediate CYP2D6 metabolizer. OBSERVATION: A 49-year-old man was receiving chronic treatment for more than 6 years with paroxetine 60 mg/day for an indication of agoraphobia. The patient ingested fifty 20 mg tablets of paroxetine in a suicide attempt. The toxic plasma level, accompanied by delirium, persisted for approximately 1 month after the overdose. According to the genotype profile, the patient was evaluated as an intermediate metabolizer with reduced CYP2D6 enzyme activity. CONCLUSION: As a consequence of the suicide attempt with overdose and the chronic paroxetine treatment that preceded it, phenoconversion to a poor metabolizer with very low CYP2D6 enzyme activity is suggested as contributing to an extremely long intoxication accompanied by delirium. Prolonged monitoring over a standard 24 h of both physical symptoms and drug plasma levels, together with a genetic profile assessment and phenoconversion consideration, is recommended after a single overdose in patients chronically treated with paroxetine.

CEITEC Central European Institute of Technology Masaryk University Brno Czechia

Center of Molecular Biology and Genetics University Hospital Brno Brno Czechia

Department of Clinical Pharmacy Hospital Pharmacy University Hospital Brno Brno Czechia

Department of Pharmacology and Toxicology Faculty of Pharmacy Masaryk University Brno Czechia

Department of Psychiatry University Hospital Brno and Faculty of Medicine Masaryk University Brno Czechia

Department of Psychiatry University Hospital Brno Brno Czechia

Laboratory of Clinical Microbiology Forlab Ltd Brno Czechia

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