Naltrexone and Breastfeeding
Naltrexone can be used during breastfeeding with caution, as only minimal amounts transfer into breast milk (total relative infant dose ~1%), but the FDA label advises caution and individual risk-benefit analysis is essential. 1, 2
FDA Labeling Position
The FDA label for naltrexone explicitly states that caution should be exercised when naltrexone is administered to a nursing woman, noting that naltrexone and its metabolite 6-β-naltrexol are excreted in rat milk, though human data are limited. 1 The label does not provide definitive guidance on whether naltrexone is safe or contraindicated, leaving the decision to clinical judgment. 1
Pharmacokinetic Evidence
The total relative infant dose of naltrexone plus its active metabolite 6-β-naltrexol is approximately 1.06% of the maternal weight-adjusted dose, which is generally considered low. 2
The primary metabolite 6-β-naltrexol accounts for most of the infant exposure (0.83% as naltrexone equivalents), while naltrexone itself contributes only 0.03%. 2
In the single published case study, only 6-β-naltrexol was detected in infant plasma at a very low concentration (1.1 mcg/L), and the 6-week-old breastfed infant showed no adverse effects and achieved expected developmental milestones. 2
Clinical Considerations
The decision to use naltrexone during breastfeeding requires individual risk-benefit analysis weighing the mother's need for opioid antagonist therapy (typically for alcohol or opioid use disorder) against the limited but reassuring safety data. 2
Key Safety Points:
Most commonly used drugs are relatively safe for breastfed babies, with doses received via milk generally much smaller than known safe doses given directly to infants. 3
The available human data, though limited to a single case report, are reassuring with no observed adverse effects in the exposed infant. 2
Naltrexone is not listed among drugs absolutely contraindicated during breastfeeding (such as anticancer drugs, lithium, oral retinoids, iodine, amiodarone, or gold salts). 3
Practical Approach
If naltrexone is deemed necessary for maternal treatment, breastfeeding can continue with close monitoring of the infant for any unusual symptoms. 2
Monitor the infant for sedation, changes in feeding patterns, or developmental concerns, though no specific adverse effects have been reported. 2
Infants less than 6 weeks of age have immature hepatic and renal function, warranting extra caution with any medication exposure through breast milk. 4
The mother should be counseled that while data are limited, the single published case showed no harm to the nursing infant. 2
Important Caveat
The evidence base consists primarily of one case report with a low naltrexone dose (5 mg/day), and the FDA label's caution reflects this limited human data. 1, 2 The lack of extensive safety data does not equate to proven harm, but clinicians should document the risk-benefit discussion with patients. 2