Haloperidol and prolactin concentrations in Asians and Caucasians.

Serum haloperidol and prolactin concentrations were measured in 34 normal male volunteers (12 Caucasians, 11 American-born Asians, and 11 foreign-born Asians) over a 7-hour period after haloperidol administration (0.5 mg given intramuscularly or 1.0 mg given orally). The results were similar between the two Asian groups but significantly different between Caucasians and Asians. After controlling for body surface area, Caucasians still had lower serum haloperidol concentrations and less prominent prolactin responses than did Asians. Furthermore, the ethnic difference in prolactin responses could not be fully accounted for by the differences in serum haloperidol concentrations between the two ethnic groups. These results indicate that both pharmacokinetic factors, including absorption and hepatic first-pass metabolism, and pharmacodynamic factors (dopamine receptor-mediated responses) contribute to the difference in responses between Caucasians and Asians.