A case of fluoxetine toxicity in a newborn of 38 weeks' gestation has been presented. The total drug concentration in cord blood was 80 ng/mL. The fluoxetine level, 26 ng/mL, is below the adult therapeutic level; the norfluoxetine cord blood level, 54 ng/mL, is at the adult therapeutic level. At 96 hours the fluoxetine level was not measurable and the norfluoxetine level was 55 ng/mL. The parent compound is fluoxetine, which is metabolized in the liver to norfluoxetine. The half-life of fluoxetine is 2 to 3 days, and that of norfluoxetine is 7 to 9 days. Interestingly, in our patient the fluoxetine was absent in the blood at 4 days, but norfluoxetine was present. The most common side effects of Prozac in adult patients involve primarily the central nervous system and include nervousness, tremor, jitteriness, and occasionally seizures. Central nervous system symptoms were most prominent in this newborn. He also had an increased heart rate. Cardiovascular side effects are less prominent in adults who are taking Prozac.
The neonate in this case was asymptomatic at 96 hours of age, indicating that the parent compound, fluoxetine, may be the active part of the drug and side effects may be caused by the parent compound.