Effects of betahistine metabolites on frog ampullar receptors

Report from a Consensus Conference on the treatment of Ménière's disease with betahistine: rationale, methodology and results

Ménière’s disease is a disorder of the inner ear that causes vertigo, tinnitus, fullness and hearing loss. Although several treatments are available, the success rate is reported to be around 70%, similar to placebo. Betahistine, a weak H1 receptor agonist and an effective H3 receptor antagonist, is frequently prescribed for Ménière’s disease, especially to reduce recurrent vertigo attacks. The effects of this drug on hearing and other audiological symptoms remains unclear. Given the inconclusive reports in the literature, we proposed a consensus conference on the use of betahistine in Ménière’s disease. The aim was to define best practice criteria for therapy for Ménière’s disease, improve clinical suitability and reduce heterogeneity of the therapeutic approach. The consensus conference on betahistine for Ménière’s disease involved a group of Italian experts in vestibular disorders who were asked a series of questions prepared by opinion leaders. The Delphi method, an iterative investigation method, was used to increase consensus. Via a tele-voting system, each participant anonymously evaluated all statements using a Likert 5-point scale. Betahistine was considered useful for the treatment of dizziness and vertigo during the intercritical phase of the disease (87% agreeing answers). However, during the acute phase of the disease betahistine was considered less effective and useful only when associated with other drugs (71% agreement). Similarly, the efficacy of the drug was considered low when used to reduce progressive hearing loss, tinnitus, and ear fullness. The experts advocated the use of betahistine during the intercritical phase of Ménière’s disease to reduce the number and severity of vertigo attacks. Its use seems to be at low risk of major side effects.

Good Clinical Approach: Delphi Consensus for the Use of Betahistine in Menière's Disease

Menière's disease is a disorder of the inner ear that causes vertigo, tinnitus, fullness, and hearing loss. Several pharmacological treatments are available, but none of them has shown significant results. Betahistine has been largely used but its effect on the main symptoms of Menière's disease remains unclear. In order to improve clinical appropriateness and to reduce the heterogeneity of the therapeutic approaches for Menière's disease, we proposed a European Consensus Conference on Betahistine's prescription. A group of European experts in vestibular disorders completed a questionnaire, prepared by opinion leaders, on the use of betahistine in Menière's disease. The Delphi method was used as an iterative investigation method in order to increase and establish the consensus. While betahistine was considered useful to reduce the number of the vertigo attacks during the intercritical phase of the disease, its use during attacks was considered helpful only when associated with other drugs. Betahistine was not considered useful for preventing hearing loss. The experts support the use of betahistine during the intercritical phase of the disease to reduce the number and severity of vertigo episodes. They also defined the parameters for a good clinical approach to evaluate the efficacy of betahistine treatment for Menière's disease.

Ménière's Syndrome or Disease: Time Trends in Management and Quality of Evidence Over the Last Two Decades

OBJECTIVE

To evaluate the evidence and trends in published literature on the treatment of Ménière's syndrome or disease (MS/D) by comparing studies published in the last two decades.

DATA SOURCES

A literature search was performed on AMED, EMBASE, HMIC, MEDLINE, PsycINFO, BNI, CINAHL, HEALTH BUSINESS ELITE, CENTRAL and Cochrane Ear, Nose and Throat disorders groups trials register using a combination of MeSH. The date of last search was October 2014.

STUDY SELECTION AND DATA EXTRACTION

Two hundred five studies (104 in decade I and 101 in decade II) were evaluated to report trends in the management of this condition, the differing levels of evidence published for each treatment modality, evaluate whether the guidelines published by the AAOHNS-Committee on Hearing and Equilibrium had been correctly employed, and whether the randomized controlled trials (RCTs) were compliant with the CONSORT guidelines.

RESULTS

The number of published RCTs almost tripled from decade I (1994-2003) to decade II (2004-2103). There was a significant decline in the use of surgical intervention (p = 0.013); however, the number of studies involving the use of intratympanic injection remained largely unchanged. There was a shift in the level of evidence in published studies; studies with level 1 evidence tripled from decade I to II (4.8 to 17.8%, respectively) (p = 0.03); however, compliance with the AAOHNS-CHE criteria for reporting treatment outcomes and the CONSORT checklist was still poor.

CONCLUSION

Although the evidence base on published literature on MS/D has improved over the last decade with an increase in emphasis on RCTs and quality of life (QoL) studies, a significant number of studies failed to follow AAOHNS-CHE criteria for reporting treatment outcome and the CONSORT criteria for reporting RCTs.

Betahistine exacerbates amikacin ototoxicity

OBJECTIVE

Betahistine augments cochlear blood flow and is currently used as an efficient therapeutic agent. Amikacin is used in a wide range of areas, but its ototoxic effect continues to be problematic. This study investigates the effect of betahistine on amikacin-induced ototoxicity.

METHODS

Thirty-two healthy rats were randomized to 4 groups of 8 rats in each group (amikacin, amikacin+betahistine, betahistine, and no treatment). Amikacin was administered intramuscularly to groups 1 and 2 for 14 days. Betahistine was delivered by oral gavage to groups 2 and 3 for 21 days. Distortion-product otoacoustic emissions (DPOAE) and auditory brainstem response (ABR) tests were conducted on all rats.

RESULTS

There were significant decreases in the DPOAE levels and significant increases in the ABR thresholds of the amikacin and amikacin+betahistine groups on the 7th, 14th, and 21st days, as compared to their basal values. The DPOAE levels of the amikacin+betahistine group significantly decreased on days 7, 14, and 21, and the ABR thresholds significantly increased on the same days, as compared to the amikacin group.

CONCLUSION

Our study implies that amikacin's ototoxic effects are augmented by the concurrent use of betahistine. Experimental and clinical research, supported by histopathological studies, is needed to affirm our findings.

Medical and noninvasive therapy for Meniere's disease

Nonoperative therapy continues to be the mainstay of treatment of patients suffering from Meniere disease. Despite extensive research, the exact pathogenesis of Meniere disease remains elusive. The poorly understood nature of this condition has made it nearly impossible to develop treatments that are curative. Most modern treatments are aimed at controlling symptoms. This article reviews the various nonoperative treatments that have been used to treat Meniere disease historically as well as outlining the authors' clinical treatment paradigm.

Neuropharmacology of vestibular system disorders

This work reviews the neuropharmacology of the vestibular system, with an emphasis on the mechanism of action of drugs used in the treatment of vestibular disorders. Otolaryngologists are confronted with a rapidly changing field in which advances in the knowledge of ionic channel function and synaptic transmission mechanisms have led to the development of new scientific models for the understanding of vestibular dysfunction and its management. In particular, there have been recent advances in our knowledge of the fundamental mechanisms of vestibular system function and drug mechanisms of action. In this work, drugs acting on vestibular system have been grouped into two main categories according to their primary mechanisms of action: those with effects on neurotransmitters and neuromodulator receptors and those that act on voltage-gated ion channels. Particular attention is given in this review to drugs that may provide additional insight into the pathophysiology of vestibular diseases. A critical review of the pharmacology and highlights of the major advances are discussed in each case.

Histamine (H3) receptors modulate the excitatory amino acid receptor response of the vestibular afferents

Although the effectiveness of histamine-related drugs in the treatment of peripheral and central vestibular disorders may be explained by their action on the vestibular nuclei, it has also been shown that antivertigo effects can take place at the peripheral level. In this work, we examined the actions of H3 histaminergic agonists and antagonists on the afferent neuron electrical discharge in the isolated inner ear of the axolotl. Our results indicate that H3 antagonists such as thioperamide, clobenpropit, and betahistine (BH) decreased the electrical discharge of afferent neurons by interfering with the postsynaptic response to excitatory amino acid agonists. These results lend further support to the idea that the antivertigo action of histamine-related drugs may be caused, at least in part, by a decrease in the sensory input from the vestibular endorgans. The present data show that the inhibitory action of the afferent neurons discharge previously described for BH is not restricted to this molecule but is also shared by other H3 antagonists.

Dose- and duration-dependent effects of betahistine dihydrochloride treatment on histamine turnover in the cat

Drugs interacting with the histaminergic system are currently used for vertigo treatment and it was shown in animal models that structural analogues of histamine like betahistine improved the recovery process after vestibular lesion. This study was aimed at determining the possible dose and duration effects of betahistine treatment on histamine turnover in normal adult cats, as judged by the level of messenger RNA for histidine decarboxylase (enzyme synthesizing histamine) in the tuberomammillary nuclei. Experiments were conducted on betahistine-treated cats receiving daily doses of 2, 5, 10, or 50 mg/kg during 1 week, 3 weeks, 2 months, or 3 months. The 1-week, 3-week, and 2- and 3-month treatments correspond to the acute, compensatory, and sustained compensatory stages of vestibular compensation, respectively. The lowest dose (2 mg/kg) given the longest time (3 months) was close to the dosage for vestibular defective patients. Data from the experimental groups were compared to control, untreated cats and to placebo-treated animals. The results clearly show that betahistine dihydrochloride administered orally in the normal cat interferes with histamine turnover by increasing the basal expression level of histidine decarboxylase mRNA of neurons located in the tuberomammillary nuclei of the posterior hypothalamus. The effects were both dose- and time-dependent. In conclusion, compensation of both static and dynamic deficits is subtended by long-term adaptive mechanisms that could be facilitated pharmacologically using betahistine dihydrochloride.

Double-blind, randomized, multicenter study comparing the effect of betahistine and flunarizine on the dizziness handicap in patients with recurrent vestibular vertigo

OBJECTIVE

The aim of this double-blind, randomized, multicenter study was to compare the efficacy of betahistine dihydrochloride (BH) and flunarizine (FL) using the Dizziness Handicap Inventory (DHI), a validated self-assessment questionnaire that has not previously been used in a clinical trial to evaluate antivertigo drugs.

MATERIAL AND METHODS

Patients with recurrent vertigo of peripheral vestibular origin and who were severely handicapped by vertigo were randomized to an 8-week course of treatment with oral BH 48 mg daily or oral FL 10 mg daily. The efficacy endpoints were the total DHI score and the physical, functional and emotional subscores.

RESULTS

Fifty-two patients completed the study. After 8 weeks of treatment the mean total DHI score and the physical subscore were significantly lower in the BH group compared to the FL group (7.5 and 3.6 points, respectively). The mean total DHI score as well as the three subscores decreased significantly after 4 and 8 weeks in both treatment groups.

CONCLUSION

This study showed that at 8 weeks BH is significantly more effective than FL in terms of improving the total DHI score and the physical subscore. It was also established that the DHI is a useful and reliable method for evaluating the efficacy of antivertigo drugs.

Binding affinity profile of betahistine and its metabolites for central histamine receptors of rodents

In order to clarify the interaction of betahistine (BH) and its metabolites [aminoethylpyridine (AEP) and hydroxyethylpyridine (HEP)] for receptors that mediate the physio-pharmacological activities of histamine, we performed in vitro competition binding studies to obtain their binding affinity profile for H(1)-, H(2)- and H(3)-histamine receptors prepared from rodent brains. Crude synaptosomal membranes were incubated in the absence (total binding) or presence of the unlabelled ligands used to saturate the specific binding, or with different concentrations of BH, AEP or HEP. Receptor binding methods were validated by running known standard drugs together with the test compounds. Like histamine, only BH interacted with H(1)-histamine receptors with comparable affinity (around 10(-5)M). BH and its metabolite AEP both interacted with the H(3)-histamine receptors, with microM affinity. HEP still showed some affinity for the H(3)-receptors but with a K(i)only 1/50 that of the parent compound. Histamine showed 10(-8)M affinity for the H(3)-receptor sites and was the only ligand to interact with H(2)-histamine receptors, all the others giving affinities above the mM range. Hill coefficients (as slopes of the sigmoidal inhibition isotherms) were close to unity for BH against H(1)- and H(3)-binding sites and for AEP against H(3)-sites, indicating that these interactions take place in the absence of cooperativity. Histamine and HEP interacted with H(1)- and H(3)-receptors with a Hill coefficient less than unity for the former and higher than unity for the latter (presence of negative and positive cooperativity, respectively). The results suggest that BH and its metabolites may act as neurotransmitter modulators of the histaminergic system.