Singulair (Montelukast) in Pregnancy
Primary Recommendation
Montelukast is classified as FDA Pregnancy Category B and can be used during pregnancy when clinically indicated for asthma or allergic rhinitis, though it should not be first-line therapy. 1
Safety Profile and Evidence Base
FDA Classification and Animal Studies
- Montelukast is FDA Pregnancy Category B, meaning no teratogenicity was observed in rats at doses up to 400 mg/kg/day (approximately 100 times the maximum recommended human dose) or in rabbits at doses up to 300 mg/kg/day (approximately 110 times the maximum recommended human dose). 1
- Animal reproduction studies showed no evidence of teratogenic effects, though animal studies are not always predictive of human response. 1
- Montelukast crosses the placenta in both rats and rabbits following oral dosing. 1
Human Pregnancy Data
- A prospective, multicentre comparative study of 180 montelukast-exposed pregnancies found no increase in the baseline rate of major malformations (1 major malformation out of 160 live births). 2
- The same study noted lower mean birth weight (3,214 ± 685 g vs 3,424 ± 551 g in non-teratogen controls, P = 0.038) and shorter gestational age, but these differences were attributed to maternal asthma severity rather than montelukast itself. 2
- During worldwide marketing experience, congenital limb defects have been rarely reported in offspring of women treated with montelukast during pregnancy, though most were taking other asthma medications and no causal relationship has been established. 1
Clinical Decision-Making Algorithm
When to Consider Montelukast
For Asthma Management:
- Consider montelukast for recalcitrant asthma if the patient showed favorable response prior to pregnancy. 3
- Inhaled corticosteroids and bronchodilators remain first-line therapy with longer safety track records. 3
- Untreated asthma with maternal hypoxia poses well-documented adverse fetal effects that may outweigh medication risks. 3
For Allergic Rhinitis:
Risk-Benefit Assessment
- Use montelukast during pregnancy only if clearly needed and when the potential maternal benefit justifies any potential fetal risk. 1
- The decision should weigh maternal risk of no therapy versus fetal risk of uncontrolled maternal disease against the risk of medication exposure. 3
- For medications with established safety profiles during pregnancy, the benefits of disease control typically far outweigh theoretical risks. 4
Important Clinical Caveats
Timing Considerations
- There is no evidence supporting the common practice of stopping immunomodulators at 32 weeks gestation based on theoretical fetal immune system concerns. 4
- Montelukast can be continued throughout pregnancy if clinically indicated for disease control. 4
Monitoring and Registry
- Merck maintains a pregnancy registry to monitor outcomes of women exposed to montelukast during pregnancy. 1
- Healthcare providers are encouraged to report prenatal exposure by calling (800) 986-8999. 1
Lactation
- Montelukast is excreted in rat milk, though it is unknown if it is excreted in human milk. 1
- Caution should be exercised when administering to nursing mothers, as many drugs are excreted in human milk. 1
Preferred Alternatives with Better Safety Data
- For asthma: Inhaled corticosteroids (particularly budesonide, which has FDA Pregnancy Category B based on human data) and inhaled beta-agonists have been used for many years without documented adverse fetal effects. 5, 3
- For allergic rhinitis: Second-generation antihistamines and intranasal corticosteroids have comparable or better safety documentation during pregnancy. 6, 3
Human pregnancy data for montelukast remain limited compared to other asthma controllers, though available evidence is reassuring. 5