Betahistine

Betahistine hydrochloride is the generic name for the anti vertigo drug SERC. It was first registered in Europe in 1970 for the treatment of Ménière's disease. It is commonly prescribed for people who have balance disorders or to alleviate the vertigo symptoms associated with Ménière's disease.

Betahistine is available in 8mg or 16mg tablets taken 3 times daily. Doses may be adjusted to between 24-48mg a day as needed. It is contraindicated for people with peptic stomach ulcers or tumours of the adrenal gland. People with bronchial asthma should be closely monitored.

Chemistry and Pharmacokinetics

Betahistine chemically is 2-[2-(methylamino) ethyl] pyridine, and is formulated as the dihydrochloride salt. Is is as close resembling between the structures of betahistine and histamine.

Betahistine comes in a tablet form and should be taken orally. It is rapidly and completely absorbed from its tablet form. The mean plasma half-life is 3-4 hours, and excretion is virtually complete in the urine within 24 hours. Plasma protein binding is very low.

The metabolism of betahistine produced two inactive metabolites, pyriylacetic acid and 2-(2-aminoethyl) pyridine.

Mode of Action

Betahistine has a very strong affinity for histamine H3 receptors and a weak affinity for histamine H1 receptors.

The mode of action of betahistine was believed to be a direct stimulating (agonistic) effect on H1 receptors located on blood vessels in the inner ear. This would give rise to local vasodilation and increased permeability, which would help reverse the underlying problem of endolympathic hydrops.

In addition, betahistine has a powerful antagonistic effects at H3 receptors, and increases the levels of neurotransmitters released from the nerve endings. This is thought to have two consequences;

  • the increased amounts of histamine released from histaminergic nerve endings can stimulate H1 receptors, thus augmenting the direct agonistic effects of betahistine on these receptors. This explains the potent vasodilatory effects of betahistine in the inner ear, which are well documented.

    • it is postulated that betahistine increases the levels of neurotransmitters such as serotonin in the brainstem, which inhibits the activity of vestibular nuclei. Means, betahistine reduce the firing rate of vestibular nuclei in the brain.

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