Which drug is a physiologic antagonist of histamine?

Which drug is a physiologic antagonist of histamine?

• A. Diphenhydramine
• B. Epinephrine
• C. Ranitidine
• D. Montelukast

Answer: (B)

A physiologic antagonist works by counteracting histamine’s effects through a different physiological pathway rather than by blocking histamine receptors directly. Epinephrine fits this role because it activates adrenergic receptors to oppose histamine-driven changes: alpha-1–mediated vasoconstriction reduces edema and hypotension, while beta-2–mediated bronchodilation relieves histamine-induced bronchoconstriction. This combination rapidly reverses the broad effects histamine can cause in allergic reactions or anaphylaxis, making it the best choice for physiologic antagonism of histamine. In contrast, the other drugs directly block histamine or its downstream mediators (for example, H1 or H2 receptor antagonists, or leukotriene receptor antagonists), which is pharmacologic antagonism rather than physiologic antagonism.

A physiologic antagonist works by counteracting histamine’s effects through a different physiological pathway rather than by blocking histamine receptors directly. Epinephrine fits this role because it activates adrenergic receptors to oppose histamine-driven changes: alpha-1–mediated vasoconstriction reduces edema and hypotension, while beta-2–mediated bronchodilation relieves histamine-induced bronchoconstriction. This combination rapidly reverses the broad effects histamine can cause in allergic reactions or anaphylaxis, making it the best choice for physiologic antagonism of histamine.

In contrast, the other drugs directly block histamine or its downstream mediators (for example, H1 or H2 receptor antagonists, or leukotriene receptor antagonists), which is pharmacologic antagonism rather than physiologic antagonism.