Which medication does not directly stimulate beta-2 receptors to relax bronchioles?

• A. Albuterol
• B. Salmeterol
• C. Ipratropium bromide
• D. Levalbuterol

Answer: (C)

Bronchodilation from beta-2 receptor stimulation works by activating those receptors on bronchial smooth muscle, which raises cAMP and causes the muscle to relax. Some medications directly target these receptors to produce fast or long-lasting bronchodilation.

Ipratropium bromide, on the other hand, is an antimuscarinic agent. It blocks acetylcholine from binding to muscarinic receptors, reducing parasympathetic-driven bronchoconstriction rather than activating beta-2 receptors. So it does not directly stimulate beta-2 receptors to relax the airways.

The other options—albuterol and levalbuterol (beta-2 agonists) and salmeterol (a long-acting beta-2 agonist)—all exert bronchodilation by directly activating beta-2 receptors.