Neuropharmacological comparison between domperidone and metoclopramide

Domperidone, a new gastrokinetic with potent antiemetic properties is devoid of central effects, up to high dose levels. To assess the CNS activity of domperidone and metoclopramide, the inhibition of intracranial self-stimulation (ICS) in two different situations, and the influence on EEG in dogs were studied. The dissociation between the antiemetic and central effects of both compounds were evaluated in dogs given a stereotypogenic dose of apomorphine. A significant and dose-related inhibition of ICS (conditioned situation) was obtained with 0.8 and 1.6 mg/kg i.v. domperidone and with 0.125, 0.25 and 0.50 mg/kg i.v. metoclopramide. The ED50 values were 0.79 mg/kg and 0.25 mg/kg respectively. The effect was most pronounced 4 hr after administration with domperidone and 15 min after administration with metoclopramide. In the EEG studies, no specific structure-related effects were found but the total potency was increased with domperidone 0.8 and 1.6 mg/kg i.v. and with metoclopramide 0.063, 0.125, 0.25 and 0.50 mg/kg i.v. This increase was due to a decrease in fast frequencies, an increase of slower frequencies and a slight increase of the amplitude. Sleep-like patterns were not observed with either compound. In the apomorphine-test in dogs, the ratio between the i.v. ED50 values for antagonism of stereotypy and of emesis was 180 (1.8/0.01) for domperidone and 2.67 (0.64/0.24) for metoclopramide. Thus, central effects and antiemetic effects are concomitant with metoclopramide, whereas with domperidone, extremely large doses are required to obtain central effects.