In most cases, the occurrence of CNS depression is consistent between the mother and the baby. If the mother suffers from symptoms of CNS depression (eg, somnolence, grogginess), a physician should examine the baby for signs of CNS depression as well. If the baby is not fed well, does not wake up to be fed, does not gain weight, or shows limpness, he or she should be examined by a physician. Central nervous system depression in the baby appears to worsen after 4 days probably, owing to the accumulation of morphine with more breastfeeding. If possible, codeine should not be used for longer than 4 days. If pain still necessitates codeine, an attempt should be made to decrease the dose or to switch to non-codeine painkillers (eg, NSAIDs). Women who convert more codeine to morphine have a duplication of the gene encoding for cytochrome P450 2D6. This genetic predisposition can be detected by genetic test. This test, although not available in most hospitals, is available on the market. Although codeine is widely used in North America, 9 randomized studies comparing the use of codeine with various NSAIDs in laparotomy cases (ie, abdominal surgery) failed to show codeine to be superior in pain relief.

CNS—central nervous system, NSAIDs—nonsteroidal anti-inflammatory drugs.