Is it safe to continue montelukast (Singulair) and cetirizine (Zyrtec) during a 17-week pregnancy?

Safety of Montelukast and Cetirizine at 17 Weeks Pregnancy

Both montelukast and cetirizine can be safely continued at 17 weeks of pregnancy, with cetirizine being one of the preferred antihistamines due to extensive safety data, and montelukast being supported by major professional societies for asthma control during pregnancy. 1, 2, 3

Cetirizine Safety Profile

Cetirizine is specifically recommended as a preferred antihistamine during pregnancy due to its established safety record. 2, 3

• Multiple guidelines identify cetirizine (along with chlorphenamine and loratadine) as preferred antihistamines over newer agents like levocetirizine, which should be avoided in the first trimester. 2, 3
• A prospective controlled study of 196 first-trimester cetirizine exposures found no increased risk of major birth defects (OR 1.07; CI 0.21-3.59) compared to controls. 4
• At 17 weeks gestation, you are past the critical organogenesis period (first trimester), making cetirizine use even more reassuring. 4

Montelukast Safety Profile

The American Congress of Obstetricians and Gynecologists and the American College of Allergy support montelukast use during pregnancy, particularly for patients with recalcitrant asthma who had favorable response before pregnancy. 1, 2

• Montelukast is FDA Pregnancy Category B, meaning animal studies show no fetal risk but human data are limited. 1, 5
• The FDA label notes that congenital limb defects have been rarely reported during post-marketing surveillance, but a causal relationship has not been established, and most women were taking multiple asthma medications. 5
• A multicentre prospective study of 180 montelukast-exposed pregnancies found no increased rate of major malformations above baseline. 6
• European guidelines classify montelukast as "probably safe" with limited data suggesting no significantly increased risk of malformations. 1

Critical Clinical Context

Poorly controlled asthma poses greater risks to maternal and fetal health than appropriate medication use. 1, 2

• 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 from these agents. 1
• Regular monitoring of asthma control is essential throughout pregnancy. 2

Practical Management Algorithm

Continue both medications if they are providing adequate symptom control:

• If montelukast was providing good asthma control before pregnancy, continuation is supported by major professional societies. 1, 2
• Cetirizine should be maintained as it is among the preferred antihistamines with the most safety data. 2, 3
• Use the lowest effective dose during pregnancy. 1

Important Caveats

• Do not assume all antihistamines have equivalent safety profiles—cetirizine is specifically preferred over newer agents. 2, 3
• If asthma control is inadequate, inhaled corticosteroids (particularly budesonide) remain first-line therapy with decades of safety data. 1
• About 1% of montelukast passes into breast milk if planning to breastfeed, but benefits generally outweigh risks. 1, 2