- betahistine dihydrochloride
POM: Prescription only medicine
This information is intended for use by health professionals
DosageAdults: Initial oral treatment is 8 to 16 mg three times daily, taken preferably with meals. Maintenance doses are generally in the range 24 - 48 mg daily. Daily dose should not exceed 48 mg. Dosage can be adjusted to suit individual patient needs. Sometimes improvement could be observed only after a couple of weeks of treatment.
Renal impairmentThere are no specific clinical trials available in this patient group, but according to post-marketing experience no dose adjustment appears to be necessary.Hepatic impairmentThere are no specific clinical trials available in this patient group, but according to post-marketing experience no dose adjustment appears to be necessary.
Elderly populationAlthough there are limited data from clinical studies in this patient group, extensive post marketing experience suggests that no dose adjustment is necessary in this population.
Paediatric population:Betahistine tablets are not recommended for use in children and adolescents below age 18 due to lack of data on safety and efficacy.
Method of administrationTake the tablets preferably with meals or after meals with a glass of water.
|Common:||nausea & dyspepsia|
|Nervous system disorders:|
|In addition to those events reported during clinical trials, the following undesirable effects have been reported spontaneously during post-marketing use and in scientific literature. A frequency cannot be estimated from the available data and is therefore classified as not known.|
|Immune system disorders:|
|Not known:||hypersensitivity reactions, e.g. anaphylaxis.|
|Not known:||Mild gastric complaints (e.g. vomiting, gastrointestinal pain, abdominal distension and bloating). These can normally be dealt with by taking the dose during meals or by lowering the dose.|
|Skin and subcutaneous tissue disorders|
|Not known:||cutaneous and subcutaneous hypersensitivity reactions, in particular angioneurotic oedema, urticarial, rash, and pruritus|
Reporting of suspected adverse reactionsReporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme at: www.mhra.gov.uk/yellowcard.
Betahistine affects the histaminergic system:Betahistine acts both as a partial histamine H1-receptor agonist and histamine H3-receptor antagonist also in neuronal tissue, and has negligible H2-receptor activity.Betahistine increases histamine turnover and release by blocking presynaptic H3-receptors and inducing H3-receptor downregulation.Betahistine may increase blood flow to the cochlear region as well as to the whole brain:Pharmacological testing in animals has shown that the blood circulation in the striae vascularis of the inner ear improves, probably by means of a relaxation of the precapillary sphincters of the microcirculation of the inner ear.Betahistine was also shown to increase cerebral blood flow in humans.
Betahistine facilitates vestibular compensation:Betahistine accelerates the vestibular recovery after unilateral neurectomy in animals, by promoting and facilitating central vestibular compensation; this effect is characterised by an up-regulation of histamine turnover and release, is mediated via the H3 Receptor antagonism.In human subjects, recovery time after vestibular neurectomy was also reduced when treated with betahistine.
Betahistine alters neuronal firing in the vestibular nuclei:Betahistine was also found to have a dose-dependent inhibiting effect on spike generation of neurons in lateral and medial vestibular nuclei.The pharmacodynamic properties as demonstrated in animals may contribute to the therapeutic benefit of betahistine in the vestibular system.The efficacy of betahistine was shown in studies in patients with vestibular vertigo and with Ménière's disease as was demonstrated by improvements in severity and frequency of vertigo attacks.
AbsorptionOrally administered betahistine is readily and almost completely absorbed from all parts of the gastro-intestinal tract. After absorption, the drug is rapidly and almost completely metabolized into 2-pyridylacetic acid. Plasma levels of betahistine are very low. Pharmacokinetic analyses are therefore based on 2-PAA measurements in plasma and urine.Under fed conditions Cmax is lower compared to fasted conditions. However, total absorption of betahistine is similar under both conditions, indicating that food intake only slows down the absorption of betahistine.
DistributionThe percentage of betahistine that is bound by blood plasma proteins is less than 5 %.
BiotransformationAfter absorption, betahistine is rapidly and almost completely metabolised into 2-PAA (which has no pharmacological activity).After oral administration of betahistine the plasma (and urinary) concentration of 2-PAA reaches its maximum 1 hour after intake and declines with a half-life of about 3.5 hours.
Excretion:2-PAA is readily excreted in the urine. In the dose range between 8 and 48 mg, about 85% of the original dose is recovered in the urine. Renal or fecal excretion of betahistine itself is of minor importance.
Linearity:Recovery rates are constant over the oral dose range of 8 48 mg indicating that the pharmacokinetics of betahistine are linear, and suggesting that the involved metabolic pathway is not saturated.
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