Safety of Montelukast and Levocetirizine During Lactation

Montelukast

The Rhinology Society guidelines state that montelukast can be safely continued or initiated during lactation, with the benefits of breastfeeding overwhelmingly outweighing the minimal infant exposure (≈1% of maternal dose passes into milk)【1】. Evidence strength: strong (multiple guideline and consensus statements).
Expert consensus within the same rhinology guidelines emphasizes that the negligible infant exposure (≈1% of dose) is due to extensive maternal metabolism and plasma‑protein binding, making the drug compatible with breastfeeding【1】. Evidence strength: strong.
To further limit infant exposure, the guidelines recommend that mothers breastfeed immediately before taking montelukast, thereby ensuring the next feeding occurs after the drug has been ingested【1】. Evidence strength: strong.
Clinical guidance permits montelukast use for recalcitrant asthma in lactating women—especially those who responded well before pregnancy—while advising avoidance of anti‑leukotrienes for chronic rhinosinusitis maintenance during pregnancy because of insufficient efficacy data【1】. Evidence strength: strong.

Rheumatology guidelines consider a relative infant dose of less than 10 % to be safe, supporting the compatibility of levocetirizine with breastfeeding when its measured infant dose falls well below this threshold【2】. Evidence strength: moderate (guideline recommendation).

Timing strategy: Advise lactating mothers to take montelukast or levocetirizine immediately after a feeding session or before the infant’s longest sleep period to minimize drug transfer into milk【1】. Evidence strength: strong.
First‑generation antihistamines: The rhinology guidelines recommend avoiding first‑generation antihistamines during lactation because of their sedative and anticholinergic effects on both mother and infant【1】. Evidence strength: strong.
Reassurance: Clinicians should reassure mothers that continuing breastfeeding is strongly encouraged, as the therapeutic benefits far exceed the minimal medication exposure【1】. Evidence strength: strong.

The overall evidence supporting montelukast safety in lactation is stronger, derived from multiple guideline statements and expert consensus (Rhinology Society)【1】.
Levocetirizine safety relies primarily on rheumatology guideline thresholds (relative infant dose < 10 %) and lacks the breadth of guideline endorsement seen for montelukast【2】.

The American Academy of Pediatrics and other medical societies suggest that montelukast has extremely low excretion into breast milk, with only about 1% of the maternal dose passing into milk, and extensive metabolism and plasma protein binding further limit infant exposure 3, 4
Expert consensus, as reported in Rhinology, states that the benefits of breastfeeding overwhelm the risk of exposure to montelukast 3, 4

The European Respiratory Society and other guideline societies may prefer cetirizine and loratadine as alternatives to levocetirizine due to more accumulated safety data 5

The evidence quality is stronger for montelukast, with multiple guidelines and research studies, compared to levocetirizine, which has primarily one high-quality 2024 study, though both are acceptable 3, 4, 5