Is dextromethorphan (DM) safe for lactating mothers?

Dextromethorphan Safety During Breastfeeding

Dextromethorphan is generally considered safe for lactating mothers with a relative infant dose of less than 1%, though caution is warranted due to limited specific guidance in breastfeeding guidelines and one reported case of rash in an exposed infant. 1

Pharmacokinetics and Breast Milk Transfer

Dextromethorphan (DM) and its active metabolite dextrorphan (DX) are distributed into breast milk with the following characteristics:

• Breast milk-to-plasma ratios of 1.0 for DM and 1.6 for DX 1
• Unbound milk-to-plasma ratios of 1.1 for DM and 2.0 for DX 1
• Estimated relative infant dose (RID) of <1% of the maternal dose 1

Safety Assessment

Evidence Supporting Safety:

• The estimated infant exposure following a single 30 mg maternal dose is minimal:

  • 0.33 ± 0.32 μg/kg/day for DM
  • 1.8 ± 1.0 μg/kg/day for DX 1

• Dextromethorphan has a well-established safety profile with infrequent and usually non-severe adverse reactions 2

Cautions:

• One nursing infant developed an erythematous rash during a clinical study of DM in breastfeeding 1
• No specific guidance on dextromethorphan during lactation is provided in the Association of Anaesthetists guidelines 3
• Extra caution should be taken with infants less than 6 weeks of age due to immature hepatic and renal function 4

Recommendations for Clinical Use

If dextromethorphan is needed by a breastfeeding mother:

1. Use the lowest effective dose for the shortest duration possible 4
2. Take the medication immediately after breastfeeding to maximize clearance time before the next feeding 4
3. Monitor the infant for potential adverse effects, particularly skin rashes 1
4. Consider alternative cough suppressants if the mother is taking monoamine oxidase inhibitors (MAOIs) due to potential drug interactions 2

Alternative Medications for Cough

If concerns exist about using dextromethorphan while breastfeeding, consider these alternatives that have more established safety profiles:

• Inhaled corticosteroids for cough associated with asthma or allergies 4
• Salbutamol for bronchospasm, which is classified as "Compatible" with breastfeeding 4

Key Points for Clinical Practice

• The benefits of treating maternal symptoms often outweigh the minimal risk of medication exposure through breast milk 4
• Standard adult dosing is typically appropriate for breastfeeding mothers 4
• Infants older than 6 months have more mature metabolism and are at lower risk for adverse effects from medications in breast milk 4
• Monitor the infant for unusual symptoms, particularly rash, irritability, or changes in feeding patterns

While the available evidence suggests dextromethorphan is likely safe during breastfeeding based on its low relative infant dose, clinicians should be aware of the limited specific guidance in breastfeeding guidelines and the isolated report of rash in an exposed infant.