Rheoencephalographic and other studies of betahistine in humans: I. The cerebral and peripheral circulatory effects of single doses in normal subjects.

Two groups of six young normal male subjects were studied by an improved form of rheoencephalography (intracranial rheoncephalography), by photoplethysmography, and by impedance plethysmography to investigate the possible effects of single doses of betahistine hydrochloride (SERC) and placebo on the normal human cranial, cerebral, scalp, and calf circulations. Two subjects participated in both groups. The results of the two studies were similar and were combined for this presentation. One subject reported slight transient faintness and visual blurring after 20 mg of the drug. No other adverse or side effects were encountered. The results show that the drug causes definite, strong, reproducible, and dose-related responses in the studied circulations, typically those of decreases in their waveform amplitudes and pulse propagation times. Betahistine hydrochloride thus acts as a potent cerebral and peripheral microcirculatory vasodilator in normal humans when given orally. Split-dose studies indicate that responses followed each dose and that the second response was superimposed on the first. The value of using betahistine hydrochloride in overlapping doses is suggested. Atypical cranial, cerebral, scalp, and calf amplitude increases were found in some high-dosage (16-mg) trials. These increases may indicate that betahistine hydrochloride can also act as an arterial vasodilator in sufficiently high dosage, but they equally may indicate that sufficiently profound microcirculatory vasodilatation can elicit secondary arterial circulatory increases.