Severe adverse effects in a newborn with two defective CYP2D6 alleles after exposure to paroxetine during late pregnancy.

Paroxetine, like other SSRIs, is reported not to increase the number of malformations in infants exposed to these drugs in utero. However, late pregnancy exposure to SSRIs sometimes leads to perinatal complications resembling the symptoms seen in serotonergic overstimulation. We report here a case of third trimester paroxetine exposure with adverse birth outcome in a newborn. The clinical symptoms in the infant included severe tremor and rigidity as well as loose stools during the first 4 days of life. Plasma paroxetine concentrations in infant plasma were quite low after birth, but she was genotyped to be a poor metabolizer of CYP2D6, the enzyme catalyzing the metabolism of paroxetine. In accordance with an earlier report, we suggest that even low plasma concentrations of paroxetine may be related to perinatal complications in infants exposed to paroxetine during late pregnancy and that the poor metabolizer genotype of CYP2D6 may be a risk factor for these complications.