Betahistine

From Wikipedia, the free encyclopedia

Betahistine
Systematic (IUPAC) name
N-methyl-2-pyridin-2-ylethanamine
Identifiers
CAS number	?
ATC code	N07CA01
PubChem	2366
Chemical data
Formula	C8H12N2
Mol. mass	136.194
Pharmacokinetic data
Bioavailability	?
Metabolism	?
Half life	?
Excretion	?
Therapeutic considerations
Pregnancy cat.	?
Legal status
Routes	?

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.

Contents 1 Chemistry and Pharmacokinetics 2 Mode of Action 3 Side Effects 4 Footnotes

[edit] Chemistry and Pharmacokinetics

Betahistine chemically is 2-[2-(methylamino) ethyl] pyridine, and is formulated as the dihydrochloride salt. Its structure closely resembles that of histamine.

Betahistine comes in tablet form and should be taken orally. It is rapidly and completely absorbed. 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.

Betahistine is transformed into aminoethylpyridine and hydroxyethylpyridine and excreted with the urine as pyridylacetic acid. There is some evidence that one of these metabolites, aminoethylpyridine, may not be inactive and exerts effects similar to those of betahistine on ampullar receptors.^[1]

A new use may be in the field of obesity management. Dr Nir Barak, of the Rabin Medical Centre in Tel Aviv has undertaken trials and it is reported (Telegraph, UK, 19 February 2007) that volunteers lost better than 1.5 Kg/week over twelve weeks and experienced a distaste for fatty foods.

[edit] 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 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.

[edit] Side Effects

• No sedation/drowsiness
• Doesn't impair driving performance
• Low level of gastric side effects
• No significant antidopaminergic effects
• Nausea can be a side effect, but the patient is generally already experiencing nausea due to the vertigo so it goes largely unnoticed.

[edit] Footnotes