Mechanism of Action
Muscarinic antagonist competitively inhibit effect of acetylcholine at muscarinic receptors – hence block the contraction of air way smooth muscle and the increase in secretion of mucus that occurs in response to vagal activity e.g atropine sulfate.
Systemic adverse effects as a result of rapid absorption include urinary retention, tachycardia, loss of accommodation and agitation and local effects like excessive dryness of mouth limits the quantity of atropine used. Ipratropium bromide is poorly absorbed and does not readily enter the central nervous system thus permits the delivery of high doses to muscarinic receptor in the airways; hence, it can safely be used for bronchial asthma.
Antimuscranic antagonist drugs appear to be slightly less effective than b- agonists agents in reversing asthmatic bronchospasm, The addition of ipratropium enhances the bronchodilation produced by nebulized albuterol in acute sever asthma. The antimuscarinic agents appear to be of significant value in chronic obstructive pulmonary diseases – perhaps more than asthma. They are useful as alternative therapies for patients intolerant of b – agonists.
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