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.