Is montelukast (Singulair) safe to use during pregnancy?

Montelukast Use During Pregnancy

Montelukast can be safely continued or initiated during pregnancy for asthma control, particularly in women who have demonstrated favorable response prior to pregnancy, though inhaled corticosteroids remain the preferred first-line therapy. 1, 2, 3

Safety Classification and Evidence Base

• Montelukast is FDA Pregnancy Category B, indicating animal studies show no fetal risk but adequate controlled human studies are limited 4
• The most recent 2020 ERS/TSANZ guidelines classify montelukast as "probably safe" with limited data suggesting no significantly increased risk of malformations, though the number of exposed women remains insufficient to ensure complete fetal safety 1
• Cases of limb reduction defects have been reported in post-marketing surveillance, though a causal relationship has not been established 1, 4

Clinical Recommendations for Asthma Management

When to Use Montelukast:

• Continue montelukast in women already well-controlled on it pre-pregnancy, as maintaining asthma control outweighs theoretical medication risks 2, 3
• Consider initiating montelukast for recalcitrant asthma when conventional inhaled medications fail to achieve adequate control 1, 2, 3
• The American Congress of Obstetricians and Gynecologists and American College of Allergy support montelukast use when clinically indicated 2

Preferred Alternatives:

• Inhaled corticosteroids (particularly budesonide) remain first-line therapy, with decades of safety data showing no adverse fetal effects 1, 2
• Short-acting beta-agonists like albuterol have extensive reassuring pregnancy data 1

Important Clinical Context

The Risk of Uncontrolled Asthma:

• Poorly controlled asthma poses definite risks to both mother and fetus, including maternal hypoxia with well-documented adverse fetal effects 2, 3
• Asthma exacerbations during pregnancy can lead to severe fetal problems and should be managed aggressively 1
• The risk of untreated severe asthma exceeds any theoretical medication risk 1

Research Evidence on Pregnancy Outcomes

• A 2022 Japanese prospective cohort study (the most recent high-quality evidence) found montelukast was not associated with increased risk of major congenital anomalies (adjusted OR 0.78,95% CI 0.23-2.05) 5
• A 2017 Danish population study of 827 montelukast-exposed pregnancies found no significant increase in major congenital anomalies, though increased risks of preterm birth and maternal complications were observed—risks known to be associated with maternal asthma itself, not the medication 6
• A 2009 multicenter prospective study found no increase in major malformations above baseline (1 malformation in 180 exposures), though lower birth weight was observed in both asthma groups regardless of medication 7

Specific Contraindications and Alternatives

• Avoid montelukast for chronic rhinosinusitis during pregnancy due to lack of efficacy data in this condition 2, 8
• For allergic rhinitis, prefer intranasal corticosteroids (particularly budesonide) or sodium cromolyn over montelukast 1, 2, 3
• Avoid 5-lipoxygenase inhibitors (zileuton) entirely in pregnancy 2

Breastfeeding Considerations

• Only approximately 1% of montelukast passes into breast milk, with extensive metabolism and plasma protein binding limiting infant exposure 2, 3
• The benefits of breastfeeding generally outweigh the minimal exposure risk 2, 3
• Consider timing breastfeeding immediately before medication intake to further minimize infant exposure 2, 3

Monitoring and Practical Management

• Use the lowest effective dose during pregnancy 2, 3
• Regular monitoring of asthma control is essential throughout pregnancy 2, 3
• Healthcare providers should report prenatal montelukast exposure to the pregnancy registry at (800) 986-8999 4
• Balance maternal risk of inadequate therapy against fetal risk of uncontrolled maternal disease when making treatment decisions 3

Common Pitfalls to Avoid

• Do not discontinue effective asthma therapy upon pregnancy recognition—uncontrolled asthma poses greater risk than medication exposure 2, 3
• Do not assume all leukotriene modifiers are equivalent; zileuton should be avoided while montelukast has acceptable safety data 2
• Recognize that observed pregnancy complications (preterm birth, lower birth weight) in studies are likely attributable to asthma severity rather than montelukast itself 7, 6