Intravenous fentanyl, morphine, and hydromorphone are commonly employed opioids for general anesthesia. Fentanyl, renowned for being approximately one hundred times more potent than morphine, exhibits high lipophilicity and the propensity to accumulate in breast tissue. A study involving five women administered 100ug of fentanyl during the induction of general anesthesia aimed to ascertain its safety. Breast milk samples were collected from the subjects at five evenly spaced intervals over a 24-hour period. The analysis revealed that less than 0.1% of the administered dose was detected in the breast milk samples collected during the specified timeframes or in the cumulative breast milk collected over the entire period. Considering the low bioavailability of fentanyl and its brief duration of action, the authors advised resuming breastfeeding in the postoperative phase once the mother has regained alertness, particularly following reasonable intraoperative fentanyl doses.
A limited study involving laboring women who received patient-controlled remifentanil during delivery revealed no discernible disparity in neonatal Apgar scores or respiratory outcomes. Another study by Stocki et al. comprised a very small cohort of four women administered remifentanil via intravenous infusion during surgery, targeting a plasma concentration of 1.5 mcg/L at the conclusion of surgery. Subsequently, infants were breastfed at intervals ranging from 1.5 to 5 hours after extubation, with no adverse respiratory effects noted in the infants. Although these studies are modest in scale, they imply that remifentanil's ultra-short context-sensitive half-life, rapid metabolism by nonspecific blood and tissue esterases, and substantial protein binding with a low drug-free fraction may render it an optimal narcotic agent for breastfeeding mothers, particularly in scenarios where minimal postoperative pain is anticipated.
Morphine, with its extended half-life and the presence of active metabolites should provoke greater apprehension among breastfeeding mothers. While occasional administration is generally regarded as acceptable, repeated dosing calls for more caution. This cautious stance is similarly advised when evaluating opioids such as meperidine and hydromorphone.
The use of meperidine by breastfeeding mothers in the postpartum period should be cautioned against due to a theoretical elevated risk of neonatal respiratory sedation. Reports have documented instances of cyanosis, bradycardia, and apnea following its administration. This phenomenon is attributed to the presence of meperidine and its metabolite normeperidine, which possess half-lives in the neonate of 13 and 65 hours, respectively. Moreover, the variability in these half-lives contributes to a broad spectrum of levels excreted in breast milk.
| Opioid | Relevant pharmacology | Breastfeeding guidance |
|---|---|---|
| Fentanyl | About 100 times more potent than morphine, highly lipophilic with a propensity to accumulate in breast tissue; less than 0.1% of a 100 µg induction dose recovered in milk over 24 hours; low bioavailability and brief duration | Resume breastfeeding postoperatively once the mother has regained alertness, particularly after reasonable intraoperative doses |
| Remifentanil | Ultra-short context-sensitive half-life, rapid metabolism by nonspecific blood and tissue esterases, substantial protein binding with a low free fraction | May be an optimal narcotic when minimal postoperative pain is anticipated; infants fed 1.5–5 hours after extubation showed no adverse respiratory effects |
| Morphine | Extended half-life with active metabolites | Occasional administration generally acceptable; repeated dosing calls for more caution |
| Hydromorphone | — | Same cautious stance advised as for morphine |
| Meperidine | Neonatal half-life of meperidine 13 hours and normeperidine 65 hours, with wide variability in levels excreted into milk | Cautioned against postpartum because of theoretical neonatal respiratory sedation; cyanosis, bradycardia, and apnea have been reported |
