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Betahistine
Betahistine hydrochloride (brand names Serc, Betaserc) is an antivertigo drug.
It was first registered in Europe in 1970 for the treatment of Ménière's disease.
It is commonly prescribed to patients with balance disorders or to alleviate vertigo symptoms associated with Ménière's disease.
Betahistine is available in 8 mg, 16 mg, or 24 mg tablets.
It is contraindicated for people with peptic ulcers or tumours of the adrenal gland. People with bronchial asthma should be closely monitored.
Its structure closely resembles that of phenethylamine and histamine.
Mode of action
Betahistine has a very strong affinity for histamine H3 receptors and a weak affinity for histamine H1 receptors. Betahistine seems to dilate the blood vessels within the middle ear which can relieve pressure from excess fluid and act on the smooth muscle.
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 endolymphatic 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.
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