The cysteinyl leukotrienes, leukotriene C4 (LTC4), LTD4, and LTE4 are pro-inflammatory agents previously known as the “slow reacting substances of anaphylaxis”. These arachidonic acid derivatives have broad ranging pro-inflammatory actions including airway smooth muscle contraction and bronchoconstriction, increase in vascular permeability, increase in mucus secretion, and inflammatory cell infiltration of lung tissue.1 The leukotriene receptor antagonists (LTRAs) zafirlukast, pranlukast, and montelukast block the effects of these mediators and are the most recently released agents with potential anti-inflammatory action for use in asthma.2 They are antagonists of LTC4, LTD4, and LTE4 and act as selective competitive antagonists of the cysteinyl leukotriene (CysLT₁) receptor, as distinct from the 5-lipoxygenase inhibitor zileuton.

An association between LTRAs and Churg-Strauss syndrome (CSS) has recently been suggested by a series of published case reports. CSS is a rare systemic vasculitis whose characteristic features include extravascular eosinophil infiltration/vasculitis, peripheral eosinophilia, and asthma. The case reports published to date describe 15 subjects, 13 of whom were being treated with zafirlukast3-7 and one with pranlukast8; a single case of pulmonary eosinophilia following treatment with montelukast9 has also been reported although this case may reasonably be reclassified as CSS. The Medicines Control Agency (UK) has received five reports of CSS associated with the use of montelukast and notes 35 such foreign …