|Systematic (IUPAC) name|
|Trade names||Serc, Veserc|
|Protein binding||Very low|
|Metabolism||To 2-(2-aminoethyl)pyridine and 2-pyridylacetic acid|
|Mol. mass||136.194 g/mol|
|(what is this?)|
Betahistine dihydrochloride (brand names Veserc, Serc, Hiserk, 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 comes in both a tablet form as well as an oral solution, and is 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 be active and exert effects similar to those of betahistine on ampullar receptors.
Mode of action
Betahistine has a very strong affinity as an antagonist for histamine H3 receptors and a weak affinity as an agonist for histamine H1 receptors. Betahistine seems to dilate the blood vessels within the inner ear which can relieve pressure from excess fluid and act on the smooth muscle.
Betahistine has two modes of action. Primarily, it has a direct stimulating (agonistic) effect on H1 receptors located on blood vessels in the inner ear. This gives rise to local vasodilation and increased permeability, which helps to reverse the underlying problem of endolymphatic hydrops.
More importantly, betahistine has a powerful antagonistic effects at H3 receptors, thereby increasing the levels of neurotransmitters histamine, acetylcholine, norepinephrine, and serotonin released from the nerve endings. The increased amounts of histamine released from histaminergic nerve endings can stimulate receptors. This stimulation explains the potent vasodilatory effects of betahistine in the inner ear, that are well documented.
- It is postulated that betahistine's increase in the level of serotonin in the brainstem inhibits the activity of vestibular nuclei.
- Low level of gastric side effects.
- Nausea can be a side effect, but the patient is generally already experiencing nausea due to the vertigo so it goes largely unnoticed.
- Patients taking betahistine dihydrochloride may experience several hypersensitivity and allergic reactions. In the November 2006 issue of "Drug Safety," Dr. Sabine Jeck-Thole and Dr. Wolfgang Wagner reported that betahistine dihydrochloride may cause several allergic and skin-related side effects. These include rash in several areas of the body; itching and hives; and swelling of the face, tongue and mouth. Other hypersensitivity reactions reported include tingling, numbness, burning sensations, shortness of breath and laboured breathing. The study authors suggest that hypersensitivity reactions may be a direct result of betahistine's role in increasing histamine levels throughout the body. Hypersensitivity reactions quickly subside after betahistine has been discontinued.
Digestive side effects Betahistine may also cause several digestive-related side effects. The package insert for Serc, a trade name for betahistine, states that patients may experience several gastrointestinal side effects. These may include nausea, upset stomach, vomiting, diarrhea and stomach cramping. These symptoms are usually not serious and subside between doses. Patients experiencing chronic digestive problems may lower their dose to the minimum effective range and by taking betahistine with meals. Additional digestive problems may require that patients consult their physician in order to find a possible suitable alternative.
Other side effects Patients taking betahistine may experience several other side effects ranging from mild to serious. The package insert for Serc states that patients may experience nervous-system side effects, including headache. Some nervous system events may also partly be attributable to the underlying condition rather than the medication used to treat it. The study by Jeck-Thole and Wagner also reports that patients may experience headache and liver problems, including increased liver enzymes and bile-flow disturbances. Any side effects that persist or outweigh the relief of symptoms of the original condition may warrant that the patient consult their physician to adjust or change the medication.