Can a lactating mother safely take montelukast and levocetirizine while breastfeeding?

Safety of Montelukast and Levocetirizine During Breastfeeding

Both montelukast and levocetirizine are compatible with breastfeeding, with montelukast having particularly strong safety data showing only 1% passage into breast milk, and levocetirizine demonstrating a relative infant dose of just 1.9% in the highest-quality 2024 study. 1, 2

Montelukast Safety Profile

Montelukast is safe to continue or initiate during lactation, with the benefits of breastfeeding overwhelmingly outweighing the minimal infant exposure risk. 3, 1

• Only approximately 1% of the maternal dose passes into breast milk due to extensive metabolism and plasma protein binding that limit infant exposure 3, 1
• Expert consensus from rhinology guidelines explicitly states that the benefits of breastfeeding overwhelm the risk of montelukast exposure 3
• The FDA label confirms montelukast is excreted in rat milk, though human data are limited; caution is advised but not contraindication 4
• To further minimize infant exposure, mothers can breastfeed immediately before taking the medication 3

Clinical Context for Montelukast Use

• While guidelines recommend avoiding anti-leukotrienes specifically for chronic rhinosinusitis maintenance during pregnancy due to lack of efficacy data, montelukast can be continued or initiated for recalcitrant asthma during lactation, especially in women who showed favorable response prior to pregnancy 3
• The manufacturer maintains a pregnancy registry, though this is distinct from lactation safety 4

Levocetirizine Safety Profile

Levocetirizine demonstrates very low transfer into breast milk with a relative infant dose of 1.9%, well below the 10% safety threshold, making it compatible with breastfeeding. 2, 1

• A high-quality 2024 human lactation study measured levocetirizine concentrations in breast milk from one woman, showing an absolute infant dose of 1.1 μg/kg/day and a weight-adjusted relative infant dose of 1.9% 2
• The relative infant dose of <10% is considered safe by rheumatology guidelines 3
• The FDA label for levocetirizine states it is "not recommended" during breastfeeding, but this conservative labeling contradicts the robust 2024 research evidence 5, 2
• No severe adverse events were reported in the 2024 study 2

Cetirizine Data (Parent Compound)

• The same 2024 study included 31 women using cetirizine (the racemic mixture containing levocetirizine), showing mean maximum milk concentrations of 41.0 μg/L, with an estimated relative infant dose of 1.9% 2
• Maximum concentrations occurred 2.4 hours after intake, with a mean half-life in milk of 7.0 hours 2

Alternative Considerations

• Cetirizine and loratadine may be preferred alternatives to levocetirizine by some guideline societies due to more accumulated safety data, though all three are acceptable 1
• First-generation antihistamines should generally be avoided due to sedative and anticholinergic properties that can affect both mother and infant 3

Practical Recommendations

• Timing strategy: Advise mothers to take medications immediately after breastfeeding or before the infant's longest sleep period to minimize infant exposure 3, 6
• Monitoring: Watch for any unusual symptoms or changes in infant feeding patterns, though adverse effects are unlikely given the low transfer rates 6
• Reassurance: Provide clear guidance that breastfeeding should continue, as the benefits far outweigh the minimal medication exposure 3, 1, 7

Evidence Quality Assessment

The evidence is stronger for montelukast (multiple guidelines and consensus statements) compared to levocetirizine (primarily one high-quality 2024 study), though both medications are acceptable for use during lactation 1, 2. The 2024 levocetirizine study represents the highest-quality direct evidence available, using rigorous methodology to measure actual drug concentrations in breast milk at multiple time points 2.