Leukotriene receptor antagonists

Leukotriene receptor antagonists (LTRAs) block the action of leukotriene D4 (and to a lesser extent leukotrienes C₄ and E₄) on the cysteinyl leukotriene receptor CysLT₁ in the lungs and bronchial tubes. This action reduces the inflammatory bronchoconstriction caused by leukotriene. LTRAs are not suitable for treating acute asthma attacks. They do not interact with theophyllines, as they operate by different molecular mechanisms.

Zafirlukast, tablets are prescribed for prophylaxis of asthma, suitable for adults and children. Zafirlukast is often used in conjunction with an inhaled steroid and/or long-acting bronchodilator. Tablets are taken on an empty stomach (one hour before, or two hours after food). Avoidance advised in patients with hepatic impairment, and moderate to severe renal impairment. Common side-effects include gastrointestinal disturbances, headache and respiratory infections.

Montelukast, orally administered drugs are prescribed for prophylaxis of asthma and to provide symptomatic relief of seasonal allergic rhinitis in asthmatic patients. Montelukast is primarily used as a complementary therapy in adults in addition to inhaled corticosteroids, if these are insufficient in controlling their asthma. In addition to film-coated tablets, montelukast is available in chewable tablets and granules that can be mixed in to cold soft food for administration. Like zafirlukast, these medications should be taken on an empty stomach. Common side-effects include gastrointestinal disturbances, headaches, hypersensitivity reactions and drowsiness. The original trade name (under patent coverage) was Singulair, but since patent expiry generic montelukast is sold under a range of brand names.

A drug acting on the same inflammatory pathway is zileuton, which inhibits the 5-LOX (5-lipoxygenase) enzyme that catalyses the formation of leukotrienes LTB₄, LTC₄, LTD₄, and LTE₄ from arachidonic acid. Although not approved for use in the UK, zileuton is approved in the US for the maintenance treatment of asthma. Common side-effects include headache and gastrointestinal disturbances (heartburn, mild stomach pain, nausea).