Metoclopramide, domperidone and dopamine in man: actions and interactions

The effects of oral doses of the dopamine antagonist antiemetics metoclopramide and domperidone on baseline and dopamine stimulated renal function and systemic haemodynamics were assessed in a placebo controlled crossover study in 9 healthy volunteers. Metoclopramide did not change baseline ERPF, GFR or FF over 2 h post dosing but it significantly reduced baseline U_NaV, U_KV, urine flow, urinary dopamine excretion, supine and erect diastolic blood pressure and supine systolic blood pressure. Domperidone and placebo did not cause these effects. Metoclopramide caused a marked rise and domperidone a small fall in plasma aldosterone concentration (PAC) but placebo was without effect. Neither antiemetic altered plasma renin activity (PRA) but a small fall occurred with placebo. Two hours after pretreatment with placebo dopamine (2 μg/kg/min) increased effective renal plasma flow (ERPF), glomerular filtration rate (GFR), sodium excretion rate (U_NaV), urine flow rate, urinary dopamine excretion rate, supine systolic blood pressure and supine and erect pulse rate and decreased the potassium excretion rate (U_KV), filtration fraction (FF) and supine diastolic blood pressure. Metoclopramide pretreatment, did not attenuate the dopamine induced rise in ERPF, GFR, urine flow, urinary dopamine excretion or supine systolic blood pressure but it did attenuate the rise in pulse rate, the fall in diastolic pressure, and the antikaliuretic effect of dopamine leading to a net kaliuresis when compared to placebo. Domperidone was similar to placebo. Neither metoclopramide nor domperidone given orally caused clinically important antagonism of the renal haemodynamic effects of dopamine. However the effects of metoclopramide on blood pressure and electrolyte excretion may have clinical importance. Metoclopramide has significant pharmacodynamic effects which are probably not due to DA₂ antagonism but may be mediated by DA₁ antagonism or be non-specific.