Rapid formation of reduced haloperidol in guinea pigs following haloperidol administration.

Haloperidol, a butyrophenone neuroleptic, is metabolically reduced in man, but not in rat and not in many other experimental animals. Here we present data that describes reductive haloperidol metabolism in guinea pigs in vivo. When haloperidol was injected intraperitoneally to guinea pigs, it was converted to reduced haloperidol so quickly that 1 hr after the injection the concentration of haloperidol was only about one fifth of that of reduced haloperidol. Dopamine metabolism was enhanced in the striatum after the administration of reduced haloperidol, but this enhancement could mostly be explained by oxidation of a small amount of reduced haloperidol back to haloperidol. The molecular mechanisms of haloperidol reduction should be further studied using guinea pigs as a model for human haloperidol metabolism.