This is an interesting group that presently appears poised to move from the uncertain role category to the more conventional category. Whereas the antihistamines used in treating vertigo are usually centrally acting histamine H1-receptor antagonists, in some parts of the world an H1+H2-receptor agonist (and possibly H3 antagonist ), Serc (betahistine), is used. According to Timmerman (quoting Laurikainen), H1 receptors do not appear to be important at all in vestibular function and the antivertiginous effects of antihistamines are mediated either through non-H1 receptors or other effects of the drugs. Also, the H1 (and H2) effects are rather minor. Accordingly, Serc’s effects might occur through H2 agonism or H3 antagonism (Timmerman, 1994). H3 is an autoreceptor that modulates H1 and H2 as well as potentially other neurotransmitter systems. Thus, an agent that primarily affected H3, could at this writing, essentially, pharmacologically do anything. The pharmacological literature is confusing as some authors suggest that betahistine is an H3 agonist (Kingma, 1997) rather than an antagonist (Timmerman, 1994).
In this condition, the person has a sensation of turning or rotation in space in the absence of actual rotation. Usually, debris from the otolithic membrane, located in the saccule and utricle, accumulates at the ampulla of the posterior semicircular canal and adheres to the cupula, making it more sensitive to angular movement. Vertigo is often accompanied by nausea, vomiting, and gait ataxia. It can be caused by peripheral vestibular lesions that affect the labyrinth of the inner ear or the vestibular division of CN VIII. It can also be caused by central lesions that affect the brainstem vestibular nuclei or their connections. Vertigo due to peripheral lesions is usually intermittent, lasts for brief periods of time, and is always accompanied by unidirectional, but not vertical, nystagmus. Vertigo due to central lesions may or may not be accompanied by nystagmus. If nystagmus is present, it may be vertical, unidirectional, or multidirectional. Some HI receptor antagonists (., the piperazine derivatives, cyclizine, and meclizine) and promethazine (a phenothiazine) have proved to be beneficial in the treatment of vertigo. Promethazine has the added advantage of relieving vomiting, which commonly accompanies vertigo.