High blood mirtazapine concentration in a newborn - A case of suspected postpartum infanticide.

We report a sudden death of an infant due to mirtazapine poisoning. A 15-day-old newborn boy was found dead when he was sleeping beside his mother who had suffered from panic disorder for approximately 1 year. After giving birth, she complained of palpitations and shaky hands, and was prescribed mirtazapine. The deceased newborn weighed 3,282 g and his height was 55 cm. There were no autopsy findings related to the death. The mirtazapine concentration as quantitated by liquid chromatography-tandem mass spectrometry analysis was 620 ng/mL in right heart blood, and was approximately 10 times higher than the therapeutic level in adults. Because transfer of mirtazapine into breast milk is low, mirtazapine was likely administered intentionally to the newborn. Based on the newborn's immature renal, liver, and blood-brain barrier function, the cause of death was attributed to mirtazapine poisoning. Poison-related homicide in the infant is rare. We report the first case of intentional mirtazapine poisoning case in a newborn.