Effect of a genetic polymorphism of CYP1A2 inducibility on the steady state plasma concentrations of haloperidol and reduced haloperidol in Japanese patients with schizophrenia

The effect of a genetic polymorphism of inducibility of cytochrome P450 (CY P) 1A2 on the steady state plasma concentrations (Css) of haloperidol and r educed haloperidol was studied to clarify if these Css are dependent on the CYP1A2 activity. The subjects were 101 Japanese schizophrenic inpatients r eceiving oral haloperidol 12 mg/d. The Css of haloperidol and reduced halop eridol were measured in duplicate by high performance liquid chromatographi c method, and were corrected to the mean body weight. A point mutation from guanine (wild-type) to adenine (mutated-type) at position - 2964 in the 5' -flanking region of CYP1A2 gene was identified by polymerase chain reaction (PCR)-fragrment length polymorphism method. Based on the present results, i.e., significant effects of CYP2D6 genotypes on the Css of haloperidol and reduced haloperidol, analyses were separately performed in two groups, i.e ., patients with 0 mutated allele of the CYP2D6 (41 cases) and those with 1 or 2 mutated alleles (10 cases). Subjects in each CYP2D6 genotype group co nsisted of 4 subgroups according to smoking habit and the presence of the m utated allele of the CYP1A2. Neither the Css of haloperidol nor that of red uced haloperidol significantly differed among the 4 subgroups in either CYP 2D6 genotype group. The present study thus suggests that the CYP1A2 activit y does not play an important role in controlling the Css of haloperidol or reduced haloperidol.