A patient with definite Meniere's disease is started on betahistine as first-line prophylactic therapy. The principal pharmacological action by which betahistine reduces the frequency of vertigo attacks is:
- A Antagonism of H3 receptors in the inner ear and brainstem, increasing release of endogenous histamine ✓
- B Blockade of H1 receptors in the vestibular nuclei, producing central vestibular suppression
- C Inhibition of type IV phosphodiesterase, reducing endolymph production by the stria vascularis
- D Selective ototoxic destruction of vestibular hair cells while sparing cochlear hair cells
Correct answer: A. Antagonism of H3 receptors in the inner ear and brainstem, increasing release of endogenous histamine
Explanation
Betahistine is a structural analogue of histamine that acts mainly as a potent H3 receptor antagonist. Blocking presynaptic H3 autoreceptors increases hypothalamic histamine release, which improves vestibular compensation and cochlear blood flow, and it has weak H1 agonist activity. Option B describes drugs like cinnarizine used for acute suppression, not prophylaxis. Option D describes intratympanic gentamicin. Betahistine does not act on the stria vascularis.
Reference: Diseases of Ear, Nose and Throat (Dhingra), 8th ed.
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