Of the new class of asthma medicines called leukotriene blockers, Singulair is the first intended for both adults and children as young as six, and the first developed for once-daily use. Singulair works by blocking leukotrienes, powerful substances that are involved in the inflammatory process associated with asthma.

Singulair has been studied for the long-term control of asthma, but is not intended for the relief of acute asthma episodes or symptoms. It should not be used to relieve an asthma episode or be abruptly substituted for oral or inhaled corticosteroids. Patients should have quick-relief medicines available to treat worsening asthma.

The marketing clearance of Singulair is based on clinical studies that measured efficacy and safety in more than 3,000 adults and children, aged six to 14 years.

In clinical studies, Singulair improved asthma control in many patients by significantly decreasing asthma attacks, preventing daytime and night-time asthma symptoms, and reducing reliance on other asthma medicines, such as quick-relieving bronchodilators. It also allowed many patients to reduce gradually their use of inhaled steroids. Inhaled steroids are the most commonly used drugs for long-term asthma control, but they can be difficult to use and have been associated with potential side effects, particularly at high doses and with long-term use. However, Singulair may not completely eliminate the need for inhaled or systemic corticosteroids. Patients should not decrease or stop taking other asthma medicines unless instructed by their doctor.

Side effects with Singulair were usually mild and generally did not require patients to stop taking Singulair. Side effects seen in adults and children during the clinical trials were similar for the groups treated with Singulair and for those treated with placebo. The most commonly reported side effects in adults for both placebo and Singulair were headache, influenza and abdominal pain. There was no increase in side effects with extended treatment, and no clinically meaningful drug interactions.