Is the medication Xone safe for a breastfeeding mother with a three-month-old preterm infant who is still regaining weight?

Xone (Naltrexone) Should Be Used with Caution During Breastfeeding, Especially in a Preterm Infant

Given the limited human data on naltrexone excretion in breast milk and the particular vulnerability of your three-month-old preterm infant who is still regaining weight, I recommend avoiding Xone (naltrexone) during breastfeeding if alternative treatments are available, or using it only if the maternal benefit clearly outweighs the potential infant risk.

Key Safety Concerns

Limited Human Data

The FDA drug label for naltrexone explicitly states that "whether or not naltrexone is excreted in human milk is unknown" 1. While animal studies show that naltrexone and its active metabolite (6-β-naltrexol) are excreted in rat milk, we cannot reliably extrapolate this to human lactation.

Heightened Risk in Preterm Infants

Your situation involves two compounding risk factors:

• Prematurity: The 2020 ERS/TSANZ guideline specifically warns that antibody/drug absorption from breast milk, while normally minimal, can be significantly increased "in pre-term infants" 2. This is because preterm infants have:

  • Increased gut permeability in the first days/weeks of life
  • Immature hepatic metabolism
  • Reduced drug clearance capacity

• Poor Weight Gain: An infant still struggling to regain weight may have compromised physiologic reserves and reduced ability to handle medication exposure

Clinical Decision Framework

If Naltrexone Is Essential:

1. Monitor the infant closely for:

   • Sedation or unusual drowsiness
   • Poor feeding or decreased appetite
   • Any withdrawal-like symptoms (irritability, restlessness)
   • Continued weight gain trajectory

2. Timing considerations:

   • The drug's pharmacokinetics are not well-characterized in breast milk
   • Without peak milk concentration data, timing feeds around doses is not evidence-based

3. Consider alternatives first:

   • Explore non-pharmacologic interventions
   • Discuss alternative medications with better lactation safety profiles

General Principles from Guidelines

The 2020 Anaesthesia guideline emphasizes that "caution should be exercised when naltrexone is administered to a nursing woman" 1. This conservative approach is particularly warranted given:

• The unknown excretion profile in human milk
• Your infant's preterm status
• The ongoing weight gain concerns

Important Caveats

• No established "safe" dose: Without human lactation data, we cannot calculate relative infant dose (RID) or establish safety thresholds
• Unknown metabolite effects: The active metabolite 6-β-naltrexol's effects on nursing infants are completely unknown 1
• Individual variation: Maternal metabolism and milk composition vary, making predictions difficult

Practical Recommendation

Work with your prescribing physician to:

1. Reassess whether naltrexone is absolutely necessary at this time
2. If essential, establish a monitoring plan with your pediatrician before starting
3. Watch for any changes in infant behavior, feeding, or weight gain
4. Have a low threshold for stopping the medication if concerns arise

The absence of human safety data, combined with your infant's preterm status and growth concerns, creates a situation where the precautionary principle should guide decision-making.