2-(2-METHYLAMINOETHYL)PYRIDINE

Indications

Betahistine is indicated in treatment of Meniere's disease (vertigo, hearing loss and tinnitus); it is not effective in preventing vertigo attacks.

Mechanism of action

The precise mechanism of betahistine's actions is unclear; it has antagonistic actions on histamine H3 receptors, and is a weak agonist at H receptors. In animal studies, it inhibits generation of spikes in vestibular nuclei. Its vasodilator activity (similar to histamine's) presumably improves blood flow in the inner ear and brainstem.

Pharmacokinetics

After oral administration, betahistine is rapidly and completely absorbed, rapidly metabolised (to one major metabolite, 2-pyridylacetic acid) and 90% excreted within 24 hours. Plasma and urinary half-lives are about 3.5 hours.

Side effects

Common adverse reactions include headache, nausea and dyspepsia. More rarely, hypersensitivity reactions (rash, pruritis, bronchospasm) and hypotension may occur.

Drug interactions

Co-administration of betahistine and monoamine oxidase inhibitors type B reduces metabolism of betahistine. Theoretically, interactions might occur with concurrent antihistamines; however, no significant problems have been reported.

Dosage forms

Betahistine is provided as scored tablets, 16 mg. Dose is 8-16 mg taken three times daily. It should be taken with food to minimise risk of GIT upsets. Patients are warned that it may take several weeks for beneficial effects to be noticed.

Precautions

Betahistine should be used with caution in individuals with asthma, urticaria, phaeochromocytoma or hypersensitivity to any components of tablets. Betahistine is contraindicated in people with active or history of peptic ulcer. Betahistine is classified in Pregnancy Safety Category B2: insufficient data available; it is contraindicated in pregnancy and lactation, and in children under 18.