Leukotriene Antagonist

INTRODUCTION:
  • Leukotriene receptor antagonists, called LTRAs for short, are a class of oral medication that is non-steroidal. 
  • They may also be referred to as anti-inflammatory bronchoconstriction preventors. 
  • LTRAs work by blocking a chemical reaction that can lead to inflammation in the airways.
MECHANISM OF ACTION:
  • There are two main approaches to block the actions of leukotrienes.
  1. Inhibition of the 5-lipoxygenase pathway
  • Drugs that inhibit the 5-lipoxygenase enzyme will inhibit the synthetic pathway of leukotriene metabolism; drugs such as MK-886 that block the 5-lipoxygenase activating protein (FLAP) inhibit functioning of the 5-lipoxygenase enzyme and may help in treating atherosclerosis.
  1. Antagonism of cysteinyl-leukotriene type 1 receptors
  • Agents such as montelukast and zafirlukast block the actions of cysteinyl leukotrienes at the CysLT1 receptor on target cells such as bronchial smooth muscle via receptor antagonism.
  • These modifiers have been shown to improve asthma symptoms, reduce asthma exacerbations and limit markers of inflammation such as eosinophil counts in the peripheral blood and bronchoalveolar lavage fluid. 
  • This demonstrates that they have anti-inflammatory properties.
MONTELUKAST:
  • Montelukast is a LTRA (Leukotriene receptor antagonist) used in maintainance therapy of asthma and relief of seasonal allergies.
  • It is not useful in acute attacks. It is usually administered orally. 
  • Montelukast is a CysLT1 antagonist; that is it blocks the action of leukotriene D4 on the cysteinyl leukotriene receptor CysLT1 in the lungs and bronchial tubes by binding to it. This reduces the bronchoconstriction otherwise caused by the leukotriene, and results in less inflammation.
  • They are indicated for prophylactic therapy of mild to moderate asthma as alternatives to inhaled glucocorticoids.
  • They are more acceptable in children.
  • They are not used for terminating asthma episodes.
  • Leukotrienes antagonists are effective in aspirin induced asthma.
  • Because of its method of operation, it is not useful for the treatment of acute asthma attacks. Again because of its very specific focus of operation, it does not interact with other allergy medications such as theophylline.
SIDE EFFECTS:
  • Side effects include gastrointestinal disturbances, hypersensitivity reactions, sleep disorders and increased bleeding tendency, aside from many other generic adverse reactions. 
  • Its use is associated with a higher incidence of Churg-Strauss syndrome
Exam Question
  • Montelukast mechanism of action is Competitive inhibition of leukotriene synthesis
  • Montelukast is leukotriene antagonist
  • The leukotriene receptor antagonist used in bronchial asthma is Zafirleukast
  • Leukotrienes antagonists are effective in aspirin induced asthma.

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