What is the mechanism of action of ipratropium bromide?

Ipratropium bromide works primarily as a short-acting muscarinic antagonist (SAMA). This means that it blocks the action of acetylcholine at muscarinic receptors in the bronchial smooth muscle. By doing so, it leads to bronchodilation, which helps alleviate symptoms of bronchospasm associated with conditions such as asthma and chronic obstructive pulmonary disease (COPD). The drug is commonly used in the management of respiratory disorders, particularly for its rapid onset of action in relieving acute symptoms.

In contrast, the other options represent different classes of medications with distinct mechanisms. Leukotriene receptor antagonists work by blocking leukotriene pathways and are primarily used for asthma management. Long-acting beta agonists (LABAs) target beta-adrenergic receptors to induce bronchodilation over a longer duration. Inhaled corticosteroids are anti-inflammatory agents that reduce airway inflammation but do not act on muscarinic receptors. Therefore, ipratropium's role as a short-acting muscarinic antagonist is what sets it apart as the correct mechanism of action in this context.