Gene involved: CYP2D6

26-year-old female who recently delivered a baby, was started on Tylenol #3 (acetaminophen/codeine) for pain.

Genetic findings:

CYP2D6 UM (ultrarapid metaboliser)

Patients who have more than 2 normal function copies of the CYP2D6 gene “ultrarapid metabolisers” are able to metabolise codeine to morphine more rapidly and more completely. As a result, even with therapeutic doses of codeine, these individuals may experience the symptoms of morphine overdose, which include extreme sleepiness, confusion, and shallow breathing, which in some instances can be fatal. Nursing mothers with ultrarapid CYP2D6 metabolism may also produce breast milk containing higher than expected levels of morphine that can lead to severe adverse events in their infants. *6 In this case it was fatal for the infant.