Therapeutic and toxic concentrations of mirtazapine

Six cases involving the antidepressant mirtazapine were analyzed in detail at the San Diego County Medical Examiner's Office from 2004 to 2005. Mirtazapine was initially detected and confirmed in each of these cases by a liquid-liquid gas chromatography (GC)-MS basic drug screen. Following another liquid-liquid basic extraction, mirtazapine was quantitated by GC with nitrogen-phosphorus detection. For each case, mirtazapine concentrations in peripheral blood (pb), central blood (cb), vitreous (vit), and liver were determined against matrix specific calibration curves (limit of detection 0.01 mg/L; linear range 0.025-1.0 mg/L). In contrast with earlier studies of postmortem distribution of mirtazapine, we found concentrations in liver that were significantly higher. Mirtazapine was identified in the cause of death by the pathologist in three cases. In the drug-related deaths, mirtazapine concentrations (mean +/- S.D.) were 2.0 +/- 1.5 mg/L (pb), 1.6 +/- 1.0 mg/L (cb), 0.78 +/- 0.56 mg/L (vit), and 10 +/- 7.4 mg/kg (liver). Alternatively, concentrations considered therapeutic (three non-drug-related deaths) were (mean +/- S.D.) 0.18 +/- 0.22 mg/L (pb), 0.16 +/- 0.17 mg/L (cb), 0.12 +/- 0.16 mg/L (vit), and 0.73 +/- 0.68 mg/kg (liver). Although mirtazapine concentrations were elevated in blood and liver in three cases, it should be noted that other drugs were also found in toxic concentrations in each case. These data may further support the fact that mirtazapine is a relatively safe drug with respect to overdose.