The effect of betahistine on gastric acid secretion and mucosal blood flow in conscious dogs

Allergic and immunologic features of Ménière's disease

Ménière's disease (MD), which by definition is idiopathic, has been ascribed to various causes, including both inhalant and food allergies. Patients with MD report higher rates of allergy history and positive skin or in vitro tests compared with a control group of patients with other otologic diseases and to the general public. Recent immunologic studies have shown higher rates of circulating immune complexes, CD4, and other immunologic components in patients with MD compared with healthy controls. Published treatment results have shown benefit from immunotherapy and/or dietary restriction for symptoms of MD in those patients who present with both allergy and MD.

Allergy and Ménière's disease

Ménière's disease (MD), which by definition is idiopathic, has been ascribed to various causes, including both inhalant and food allergies. Patients with MD report higher rates of allergy history and positive skin or in vitro tests compared to a control group of patients with other otologic diseases and to the general public. Recent immunologic studies have shown higher rates of circulating immune complexes, CD4, and other immunologic components in patients with MD compared to normal controls. Published treatment results have shown benefit from immunotherapy and/or dietary restriction for symptoms of MD in patients with both allergy and MD.

Betahistine: a retrospective synopsis of safety data

Betahistine is a structural analogue of histamine that is prescribed for the treatment of vestibular disorders such as Ménière's disease and the symptomatic treatment of vertigo. It is estimated from sales information that >130 million patients have been exposed to the drug since its registration in 1968. In this review we analyse the safety profile of betahistine based on data obtained during >35 years of worldwide postmarketing surveillance. Until 31 December 2005, 554 adverse drug reaction (ADR) reports with 994 individual signs and symptoms were received by the marketing authorisation holder from worldwide sources and were reviewed and evaluated. Signs and symptoms of cutaneous hypersensitivity reactions during betahistine therapy were the most frequently reported complaints. They consisted of usually mild and self-limiting rash, pruritus and urticaria, and all symptoms were reversible after drug discontinuation. Betahistine was reported to be involved in one anaphylactoid reaction and one case of Stevens-Johnson syndrome. Anaphylactic reactions with fatal outcome were not reported. The reports that describe gastrointestinal complaints mostly concern nausea and vomiting or unspecific abdominal pain. These were typically non-serious complaints. Hepatobiliary involvement was reported 25 times, including increases in alkaline phosphatase, gamma-glutamyltransferase, and alanine and aspartate aminotransferase levels. None of the patients concerned developed severe liver failure or died. ADRs related to the nervous system predominantly reveal heterogeneous events that are not suggestive of a specific adverse reaction profile for betahistine. A clinical intolerance to betahistine that gave rise to asthma or bronchospasm was only reported in eight ADRs. A total of three cases of neoplasm have been reported. One case concerned a male patient of unknown age who experienced weight loss, insomnia, impatience and irritability soon after the start of betahistine therapy. An undiagnosed phaeochromocytoma was suspected. The remaining two cases were assessed as being unrelated to betahistine by the reporter. Finally, four deaths have been reported during the course of postmarketing surveillance for betahistine. The reporter assessed the causal relationship to betahistine in two as unrelated, in one as unlikely and the other as unassessable. In summary, clinical and postmarketing studies have revealed a good safety profile of betahistine that was confirmed by the safety surveillance data presented.

Some studies of the action of betahistine at H1 and H2 receptors for histamine

Betahistine produced a concentration-dependent contraction of the guinea-pig ileum and was about 27 times less active than histamine in this respect. Betahistine induced desensitization of contractile responses to histamine in the guinea-pig ileum. The H1 histamine receptor antagonist mepyramine was a competitive antagonist of the action of betahistine on the guinea-pig ileum. Betahistine caused relaxation of the rat uterus contracted by acetylcholine, and this action of betahistine was blocked by the H2 receptor antagonist cimetidine. Betahistine had a concentration-dependent positive chronotropic action on isolated guinea-pig atria, and in this respect was tenfold less potent than histamine. The action of betahistine on the atria was blocked by the H2 receptor antagonist YM11170. Betahistine caused a concentration-related contraction of the isolated lung parenchymal strip of the guinea-pig, and YM11170 potentiated this effect. Betahistine failed to release histamine from rat peritoneal mast cells at concentrations up to 100 microM and it did not prevent histamine release induced by either substance P or anti-IgE. Betahistine produced a dose-related flare and wheal reaction when injected intradermally into human skin. It is concluded that betahistine has agonist activity at both H1 and H2 receptors for histamine.

Studies on histamine H2 receptors coupled to cardiac adenylate cyclase. Effects of guanylnucleotides and structural requirements for agonist activity

In particulate preparations from guinea-pig ventricle, histamine in the concentration range 10(-6)--10(-3) M caused a 3--5fold stimulation of adenylate cyclase activity which was dependent on the presence of GTP. The effects of fourteen analogs of histamine were examined on this cyclase preparation. Five of the compounds studied proved to be partial agonists relative to histamine while nine others had essentially the same intrinsic activity as histamine. The intrinsic activities of the partial agonists were increased by GppNHp to the extent that dimaprit, which was a partial agonist in the presence of GTP, became a full agonist in the presence of GppNHp. The relative potencies of the full agonists as activators of the cyclase were found to correlate with the relative potencies on physiologically defined H2 receptor systems. Activation of the cyclase by histamine, as well as by several of the agonist analogs, including dimaprit and tolazoline, was completely blocked by the H2 antagonist cimetidine, but was not affected by pharmacologically relevant concentrations of the H1 antagonist mepyramine, the beta-blocker alprenolol, or the alpha-blocker phentolamine. The results suggest that all the agonists studied probably interact with a common H2 receptor site on the cardiac muscle cell leading to activation of adenylate cyclase. The accompanying increase in cyclic AMP is presumably responsible for the chronotropic and inotropic effects of histamine and related compounds on cardiac muscle.

Liberation of histamine by compound 48/80, tolazoline, betahistine and burimamide from isolated spontaneously beating guinea pig and rabbit atrial pairs

Tolazoline, betahistine, burimamide and compound 48/80 release histamine from isolated guinea pig atria resulting in histamine concentrations that stimulate H2-receptors. Tolazoline, burimamide and 48/80 also release histamine from rabbit atria but do not result in histamine concentrations that will stimulate either H1- or H2-receptors. However, betahistine (which does not release histamine from rabbit atria) and tolazoline stimulate the rabbit atrial chronotropic response by releasing catecholamines.