Ipratropium bromide is preferred over atropine as an inhaled bronchodilator in chronic obstructive pulmonary disease chiefly because:

• A It selectively blocks M3 receptors while sparing M2 receptors
• B It inhibits phosphodiesterase-4, unlike atropine
• C It has intrinsic beta-2 agonist activity providing additive bronchodilation
• D Its quaternary ammonium structure limits systemic absorption and central anticholinergic effects ✓

Explanation

Ipratropium is a quaternary ammonium derivative of atropine. Because it carries a permanent positive charge it is poorly absorbed across mucous membranes and the blood-brain barrier, so inhaled therapy gives local bronchodilation with minimal systemic anticholinergic toxicity. It blocks M3 and M2 receptors equally, has no adrenergic or phosphodiesterase activity, and tiotropium rather than ipratropium is the long-acting M3-preferred analogue.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

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Written and medically reviewed by the StethoPrep medical team.