codeine

Note: Codeine is metabolised by cytochrome P450 2D6 (CYP2D6) to morphine. The CYP2D6 ultrarapid metaboliser phenotype occurs in 1% to 10% of Western European populations (depending on country of origin) but up to 30% in people of North African descent. During repeated codeine therapy at usual analgesic doses, breastfeeding people with the CYP2D6 ultrarapid metaboliser phenotype produce significant amounts of morphine, which transfer through the milk to the infant. Over several days of therapy, the morphine may accumulate resulting in severe infant toxicity (central nervous system depression) and even death. Genotyping of pregnant people before the birth of their infant may predict the risk, but such tests are not routinely available.