Interactions between domperidone and ropinirole, a novel dopamine D2-receptor agonist.

1. Ropinirole, SK&F 101468 has been characterized preclinically as a specific dopamine D2-receptor agonist. Nine male healthy subjects were investigated for the effects on supine and erect heart rate and blood pressure, catecholamines and prolactin, of a single dose of 800 micrograms ropinirole preceded by a single dose of 20 mg domperidone or domperidone-placebo, and those of a single dose of domperidone followed by ropinirole-placebo. 2. Single doses of 800 micrograms ropinirole did not cause clinically significant changes in supine resting heart rate and blood pressure. However, they caused postural faintness on 3 min immobile upright standing on 10/26 occasions. 3. Pretreatment with 20 mg domperidone 1 h before administration of ropinirole prevented the postural symptoms in all but one subject. It did not alter ropinirole's plasma pharmacokinetics. 4. Ropinirole did not alter supine or standing catecholamine concentrations. 5. Domperidone increased the plasma concentrations of prolactin whereas ropinirole administered alone reduced them. A single dose of 800 micrograms ropinirole did not attenuate the prolactin increase induced by a single dose of 20 mg domperidone administered 1 h earlier.