Is Montelukast (Singulair) safe to use during pregnancy?

Is Montelukast Safe in Pregnancy?

Yes, montelukast is safe to use during pregnancy and is classified as FDA Pregnancy Category B, meaning it can be continued or initiated during pregnancy, particularly for patients with asthma who have shown favorable response prior to conception. 1, 2, 3

FDA Classification and Safety Profile

• Montelukast holds FDA Pregnancy Category B classification based on reassuring animal reproductive studies showing no teratogenic effects at doses far exceeding human exposure, and accumulating human safety data. 1, 3

• Animal studies in rats (up to 400 mg/kg/day) and rabbits (up to 300 mg/kg/day) showed no teratogenicity at exposures approximately 100-110 times the maximum recommended human dose. 3

• The drug crosses the placenta in animal studies, but adequate controlled studies in pregnant women remain limited. 3

Clinical Guidelines and Recommendations

Major medical societies including the American Congress of Obstetricians and Gynecologists and the American College of Allergy support montelukast use during pregnancy when clinically indicated, especially for recalcitrant asthma. 2, 4, 5

• Continue montelukast throughout pregnancy if it provided effective asthma control before conception, as poorly controlled asthma poses greater risks to maternal and fetal health than the medication itself. 2, 4

• Montelukast can be initiated during pregnancy for patients with difficult-to-control asthma, though inhaled corticosteroids remain first-line therapy. 2, 4

• Use the lowest effective dose during pregnancy, as recommended for all medications in this setting. 2

Human Pregnancy Data

The available human evidence is reassuring regarding major malformations:

• A prospective multicenter study of 180 montelukast-exposed pregnancies found only 1 major malformation among 160 live births (0.6%), which does not exceed the 1-3% baseline population risk. 6

• A large Danish population study of 827 pregnancies exposed to montelukast found no significant increase in major congenital anomalies (adjusted OR 1.4,95% CI 0.9-2.3 for montelukast alone; OR 1.0,95% CI 0.6-1.8 for montelukast with other asthma medications). 7

• A Japanese prospective cohort study of 231 LTRA-exposed pregnancies (including 122 montelukast exposures) found a 1.9% rate of major congenital anomalies with no increased risk compared to controls (adjusted OR 0.78,95% CI 0.23-2.05). 8

Important Considerations and Caveats

Lower birth weight and shorter gestational age have been observed in some studies, but these appear related to maternal asthma severity rather than montelukast exposure itself:

• One study found mean birth weight 304g lower in montelukast-exposed infants, but this difference was present in both asthma groups (montelukast and disease-matched controls), suggesting the association is with maternal asthma rather than the medication. 6

• Increased rates of preterm birth and maternal complications (preeclampsia, gestational diabetes) were noted in Danish data, but these are known complications of poorly controlled asthma itself. 7

• About 25% of newborns had fetal distress in one study, though this finding requires cautious interpretation given the underlying maternal disease. 6

Breastfeeding Safety

• Only about 1% of montelukast passes into breast milk, and extensive metabolism plus plasma protein binding further limit infant exposure. 2, 4

• The benefits of breastfeeding generally outweigh the minimal risk of exposure; consider timing breastfeeding prior to medication intake to further minimize infant exposure. 2, 4

Clinical Algorithm for Use

For asthma during pregnancy:

1. Continue montelukast if it provided good control before pregnancy 2, 4
2. Initiate montelukast for recalcitrant asthma not controlled by inhaled corticosteroids 2, 4
3. Monitor asthma control regularly, as uncontrolled asthma poses greater fetal risks than medication 2, 4

For allergic rhinitis during pregnancy:

• Montelukast can be used if there was favorable pre-pregnancy response, though intranasal corticosteroids (particularly budesonide) or sodium cromolyn are preferred first-line options. 1, 5
• Montelukast is generally not recommended for chronic rhinosinusitis maintenance during pregnancy due to lack of efficacy data in this condition. 2

Key Pitfalls to Avoid

• Do not discontinue effective asthma therapy due to pregnancy concerns - poorly controlled asthma is more dangerous to mother and fetus than montelukast exposure. 2, 4

• Do not confuse montelukast with zileuton - 5-lipoxygenase inhibitors like zileuton should be avoided in pregnancy, but montelukast (a leukotriene receptor antagonist) is safe. 2

• Do not assume all asthma medications have equivalent pregnancy safety - while montelukast is Category B, individual agents have different evidence bases and should be evaluated separately. 4