Singulair is a medication used for the treatment of the symptoms of both asthma and seasonal allergies. As a product, it is akin to Advair. It is a prophylactic and chronic treatment designed for use on a daily basis and not for acute asthmatic attacks (a β-agonist inhaler like Albuterol should be used in these cases). Singulair was originally released for treatment of asthma-related symptoms in 1998. In 2003, the FDA approved its use seasonal allergies (to treat symptoms such as rhinitis, itchy eyes, postnasal drip, etc.).

Recent research has identified a group of compounds called leukotrienes that, in an overabundance, can lead to asthma and allergic reactions. "Leukotrienes are biologically active compounds formed [from the metabolism of] arachidonic acid and other polyunsaturated fatty acids," writes Prof. Bengt Samuelsson2. "Leukotrienes are of importance in host defense reactions and have a pathophysioloigcal role in inflammation and allergic reactions." However, in some people, the levels of leukotrienes present in the lungs and brochia are too high and cause a massive inflammatory response, severely narrowing the passages to and from the lungs. This leads to the classic "asthma attack" symptoms - wheezing and shortness of breath.

The active ingredient in Singulair is montelukast sodium, part of the leukotriene-antagonist class of medications. As a selective and orally active leukotriene receptor antagonist, Singulair inhibits the cysteinyl leukotriene CysLT1 receptor, thereby stopping the production of leukotrienes. The Merck monograph3 states:

Montelukast is an orally active compound that binds with high affinity and selectivity to the CysLT1 receptor (in preference to other pharmacologically important airway receptors, such as the prostanoid, cholinergic, or β-adrenergic receptor). Montelukast inhibits physiologic actions of LTD4 at the CysLT1 receptor without any agonist activity.

Montelukast sodium is described chemically as:

[R-(E)]-1-[[[1-[3-[2-(7-chloro-2- quinolinyl)ethenyl]phenyl]-3-[2-(1-hydroxy-1-methylethyl)phenyl]propyl]thio]methyl]cyclopropaneacetic acid, monosodium salt.
The empirical formula is C35H35ClNNaO3S, and its molecular weight is 608.18.

Singulair is distributed in multiple forms due to the fact that it has been approved for and is used in just about every age group - from as young as 12 months on up.

  • For adults and adolescents (15 years and older), a 10mg tablet is available (contains 10.4mg of montelukast sodium);
  • For older children (between ages 6 and 11), 4mg and 5mg chewable tablets are available (4.2mg and 5.2mg montelukast sodium, respectively); Phenylketonuric patients should be aware that the 4mg and 5mg chewable tablets contain phenylalanine (a component of aspartame), 0.674mg and 0.842mg per 4mg and 5mg chewable tablet, respectively;
  • And, for very young children (aged 12 months* to 5 years), the medicine is available in a powdered state (called oral granules) that can be mixed with juice or other liquid for ingestion; each packet contains 4mg montelukast (4.2mg montelukast sodium).

Side effects during clinical trials included headache, ear infection, sore throat, and upper respiratory infection. These were generally mild and none of the clinical participants stopped using the medication because of these effects.

Many clinical trials have been held that have proven the efficacy of Singulair compared to placebo for all forms of asthma as well as seasonal allergies. For details on these trials, please refer to the Merck monograph (available from the Singulair Web site1 under the "Healthcare Providers" section).

* = Note: Infants as young as 12 months have only been studied for asthmatic patients. For seasonal allergies, 2 years is the preferred minimum age for prescibing Singulair.


1. Singulair. Merck. 10/10/2003.
2. Biochemical studies of leukotrienes. Bengt Samuelsson, Professor, M.D., PhD. at Karolinska institutet. 10/10/2003.
3. Singulair Monograph (9088817). Merck & Co., Inc. May 2003.
4. U.S. Food and Drug Administration (FDA).

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