In 2015 more than 30,000 deaths from opioid overdose were reported (FIGURE).1 More than 50% of the deaths were due to prescription opioids. The opioid crisis is a public health emergency and clinicians are diligently working to reduce both the number of opioid prescriptions and the doses prescribed per prescription.
In obstetrics, there is growing concern that narcotics used for the treatment of pain in women who are breastfeeding may increase the risk of adverse effects in newborns, including excessive sedation and respiratory depression. The American Academy of Pediatrics (AAP), the US Food and Drug Administration (FDA) and the American College of Obstetricians and Gynecologists (ACOG) recommend against the use of codeine and tramadol in women who are breastfeeding because their newborns may have adverse reactions, including excessive sleepiness, difficulty breathing, and potentially fatal breathing problems.2–4 In addition, there is growing concern that the use of oxycodone and hydrocodone should also be limited in women who are breastfeeding. In this article, I discuss the rationale for these recommendations.
Landmark women’s health care remains law of the land
Codeine is metabolized to morphine by CYP2D6 and CYP2D7. Both codeine and morphine are excreted into breast milk. Some women are ultrarapid metabolizers of codeine because of high levels of CYP2D6, resulting in higher concentrations of morphine in their breast milk and their breast fed newborn.2,5 In many women who are ultra-rapid metabolizers of codeine, CYP2D6 gene duplication or multiplication is the cause of the increased enzyme activity.6 Genotyping can identify some women who are ultrarapid metabolizers, but it is not currently utilized widely in clinical practice.
In the United States approximately 5% of women express high levels of CYP2D6 and are ultra-rapid metabolizers of codeine.4 In Ethiopia as many as 29% of women are ultrarapid metabolizers.7 Newborn central nervous system (CNS) depression is the most common adverse effect of fetal ingestion of excessive codeine and mor-phine from breast milk and may present as sedation, apnea, bradycardia, or cyanosis.8 Multiple newborn fatalities have been re-ported in the literature when lactating mothers who were ultrarapid metabolizers took co-deine. The FDA and ACOG recommend against the use of codeine in lactating women.
Hydrocodone, a hydrogenated ketone derivative of codeine, is metabolized by CYP2D6 to hydromorphone. Both hydrocodone and hydromorphone are present in breast milk. In lactating mothers taking hydrocodone, up to 9% of the dose may be ingested by the breastfeeding newborn.9 There is concern that hydrocodone use by women who are breastfeeding and are ultrarapid metabolizers may cause increased fetal consumption of hydromorphone resulting in adverse outcomes in the newborn. The AAP cautions against the use of hydrocodone.2
Oxycodone is metabolized by CYP2D6 to oxymorphone and is concentrated into breast milk.10 Oxymorphone is more than 10 times more potent than oxycodone. In one study of lactating women taking oxycodone, codeine, or acetaminophen, the rates of neonate CNS depression were 20%, 17%, and 0.5%, respectively.11 The authors concluded that for mothers who are breastfeeding oxycodone was no safer than codeine because both medications were associated with a high rate of depression in the neonate. Newborns who develop CNS depression from exposure to oxycodone in breast milk will respond to naloxone treatment.12 The AAP recommends against prescribing oxycodone for women who are breastfeeding their infants.2
In a recent communication, the Society for Obstetric Anesthesia and Perinatology (SOAP) observed that in the United States, following cesarean delivery the majority of women receive oxycodone or hydrocodone.13 SOAP disagreed with the AAP recommendation against the use of oxycodone or hydrocodone in breastfeeding women. SOAP noted that all narcotics can produce adverse effects in newborns of breastfeeding women and that there are no good data that the prescription of oxycodone or hydrocodone is more risky than morphine or hydromorphone. However, based on their assessment of risk and benefit, pediatricians prioritize the use of acetaminophen and morphine and seldom use oxycodone or hydrocodone to treat moderate to severe pain in babies and children.
Tramadol is metabolized by CYP2D6 to O-desmethyltramadol. Both tramadol and O-desmethyltramadol are excreted into breast milk. In ultrarapid metabolizers, a greater concentration of O-desmethyltramadol is excreted into breast milk. The FDA reported that they identified no serious neonatal adverse events in the literature due to the use of tramadol by women who are breastfeeding. However, given that tramadol and its CYP2D6 metabolite enter breast milk and the potential for life-threatening respiratory de-pression in the infant, the FDA included tramadol in its warning about codeine.3
Codeine, hydrocodone, oxycodone, and tramadol are all metabolized to more potent metabolites by the CYP2D6 enzyme. Individuals with low CYP2D6 activity, representing about 5% of the US population, cannot fully activate these narcotics. Hence they may not get adequate pain relief when treated with codeine, oxycodone, hydrocodone, or tramadol. Given their resistance to these medications they may first be placed on a higher dose of the narcotic and then switched from a high ineffective dose of one of the agents activated by CYP2D6 to a high dose of morphine or hydromorphone. This can be dangerous because they may then receive an excessive dose of narcotic and develop respiratory depression.14