Introduction
This medical condition appears almost balanced between sexes (53% female) and reports increase with aging. Tinnitus is commonly associated with hearing loss of up to 90%. Chronic tinnitus occurs when the symptom persists for longer than six months1. About 40% of tinnitus are idiopathic, termed ‘primary tinnitus’, up to 20% have disabling effects such as insomnia, anxiety, and depression and is referred to as ‘bothersome tinnitus2.
Different causes of tinnitus, such as, acoustic trauma, emotional distress, and metabolic disorders promote cochlear disfunction1. Postulated theories, such as discordant damage theory and maladaptive neuroplastic response theory, predict that the cochlear disfunction reduces cochlear nerve inhibition, resulting in hyperexcitability of the auditory neural center perceived as tinnitus3. There is no standard treatment across a wide range of interventions, such as transcranial magnetic stimulation, sounds, and cognitive-behavioral therapies; moreover, many of them are difficult to access4, 5.
Betahistine dihydrochloride was initially indicated for Ménière’s disease, but its empirical use for primary tinnitus has progressively increased in several countrie6. For instance, in the United Kingdom it was the most prescribed tinnitus medication by otolaryngologists and the second by general practitioners7. The drug is a weak histamine H1 receptor agonist and a potent histamine H3 receptor antagonist.3 It is believed to improve cochlear blood flow8 and neural function,9diminishing the effects of cochlear disfunction and central auditory hyperactivity.
This is encouraged by promising scientific results (32.8% of clinical improvement vs. 17.0% untreated);10,11 safety (similar to the placebo);3 and accessibility even in emerging countries (e.g., one month of treatment cost about 5.0% of the Brazilian minimal wage). However, in a recent systematic review by Wegner et al.3, only five clinical trials were selected, all of which were compromised by methodologic flaws.