What are the guidelines for using Montelukast (Singulair) during pregnancy?

Montelukast Use During Pregnancy

Direct Recommendation

Montelukast is safe to use during pregnancy for asthma management, particularly when there has been a favorable prepregnancy response, and should be continued or initiated when needed for adequate asthma control. 1, 2, 3

Safety Classification and Evidence Base

Montelukast is FDA Pregnancy Category B, meaning animal reproduction studies have shown no fetal risk, though adequate controlled human studies are limited. 4 The drug crosses the placenta in animal studies, but extensive human observational data has been reassuring. 4

Key Safety Data:

• No increased risk of major congenital malformations above the 1-3% baseline rate has been demonstrated across multiple studies. 5, 6, 7, 8
• A 2024 meta-analysis found no significant increase in congenital anomalies with pooled risk ratio of 1.13 [95% CI (0.74,1.73), p = 0.56]. 8
• A 2022 Japanese prospective cohort study of 231 pregnancies exposed to leukotriene receptor antagonists found major congenital anomaly rate of only 1.9%, with adjusted odds ratio of 0.78 (95% CI 0.23-2.05, p = 0.653). 6
• Post-marketing surveillance has reported rare cases of congenital limb defects, but a causal relationship has not been established, and most women were taking multiple asthma medications. 4

Clinical Indications and Guidelines

For Asthma Management:

Montelukast should be used for recalcitrant asthma during pregnancy, especially in patients who demonstrated uniquely favorable response before pregnancy. 1, 2, 3 The American Congress of Obstetricians and Gynecologists and the American College of Allergy support this approach. 2, 9

Treatment Algorithm:

1. First-line therapy remains inhaled corticosteroids (particularly budesonide, which has the most extensive human safety data and is also Pregnancy Category B). 2, 3
2. Add montelukast when inhaled medications alone fail to achieve adequate asthma control. 2
3. Continue montelukast if the patient was well-controlled on it prior to pregnancy. 1, 2, 3
4. Use the lowest effective dose during pregnancy. 2, 3

For Allergic Rhinitis:

Montelukast can be used for allergic rhinitis during pregnancy, but intranasal corticosteroids (particularly budesonide) or sodium cromolyn are preferred first-line options. 1, 9 The same guidelines that apply to asthma management should be followed—use montelukast when there has been a uniquely favorable prepregnancy response. 1

Montelukast is generally not recommended for chronic rhinosinusitis maintenance during pregnancy due to lack of efficacy data in this condition. 2

Important Maternal and Fetal Considerations

Potential Associations (Not Causally Established):

• Lower birth weight: Studies have shown mean birth weight approximately 200-300g lower in montelukast-exposed pregnancies, but this is likely attributable to maternal asthma severity rather than the medication itself. 5, 8
• Preterm delivery: Meta-analysis showed increased odds ratio of 1.82 [95% CI (1.35,2.45)] for preterm delivery and low birthweight combined. 8 However, Danish population data suggests this risk is associated with maternal asthma complications rather than montelukast specifically. 7
• Maternal complications: Increased risk of preeclampsia and gestational diabetes has been observed, but these are known complications of poorly controlled asthma. 7

Critical Context:

Poorly controlled asthma poses far greater risks to maternal and fetal health than appropriate medication use. 2, 3, 9 Asthma exacerbations during pregnancy can lead to severe fetal problems and must be managed aggressively. 2

Breastfeeding Guidance

Montelukast is safe during breastfeeding. 2, 3, 9 Only about 1% of the drug passes into breast milk, and extensive metabolism plus plasma protein binding limit infant exposure. 2, 3, 9 The benefits of breastfeeding outweigh any theoretical risk. 2, 9 Consider timing breastfeeding prior to medication intake to further minimize infant exposure. 2, 9

Monitoring Requirements

• Regular monitoring of asthma control is essential throughout pregnancy. 2, 3
• Taper to the lowest effective dose that maintains adequate control. 1, 2
• Healthcare providers should report any prenatal exposure to the pregnancy registry at (800) 986-8999. 4

Critical Pitfalls to Avoid

• Do not discontinue effective asthma therapy due to pregnancy concerns—uncontrolled asthma is more dangerous than medication exposure. 2, 3, 9
• Avoid oral decongestants during the first trimester if treating rhinitis, as they are associated with increased risk of gastroschisis and small intestinal atresia. 1, 9
• Do not use zileuton (5-lipoxygenase inhibitor) in pregnant or lactating mothers—this is contraindicated. 2
• Do not assume all leukotriene modifiers have the same safety profile—montelukast and pranlukast have more data than zafirlukast. 6