Hideki Morishita

Haplotype structures of the UGT1A gene complex in a Japanese population.

Genetic polymorphisms of UDP-glucuronosyltransferases (UGTs) are involved in individual and ethnic differences in drug metabolism. To reveal co-occurrence of the UGT1A polymorphisms, we first analyzed haplotype structures of the entire UGT1A gene complex using the polymorphisms from 196 Japanese subjects. Based on strong linkage disequilibrium between UGT1A8 and 1A10, among 1A9, 1A7, and 1A6, and between 1A3 and 1A1, the complex was divided into five blocks, Block 8/10, Block 9/6, Block 4, Block 3/1, and Block C, and the haplotypes for each block were subsequently determined/inferred. Second, using pyrosequencing or direct sequencing, additional 105 subjects were genotyped for 41 functionally tagged polymorphisms. The data from 301 subjects confirmed the robustness of block partitioning, but several linkages among the haplotypes with functional changes were found across the blocks. Thus, important haplotypes and their linkages were identified among the UGT1A gene blocks (and segments), which should be considered in pharmacogenetic studies.

Genetic Variations and Haplotype Structures of the ABCB1 Gene in a Japanese Population: An Expanded Haplotype Block Covering the Distal Promoter Region, and Associated Ethnic Differences

As functional ABCB1 haplotypes were recently reported in the promoter region of the gene, we resequenced the ABCB1 distal promoter region, along with other regions (the enhancer and proximal promoter regions, and all 28 exons), in a total of 533 Japanese subjects. Linkage disequilibrium (LD) analysis based on 92 genetic variations revealed 4 LD blocks with the same make up as previously described (Blocks −1, 1, 2 and 3), except that Block 1 was expanded to include the distal promoter region, and that a new linkage between polymorphisms −1789G>A in the distal promoter region and IVS5 + 123A>G in intron 5 was identified. We re‐assigned Block 1 haplotypes, and added novel haplotypes to the other 3 blocks. The reported promoter haplotypes were further classified into several types according to tagging variations within Block 1 coding or intronic regions. Our current data reconfirm the haplotype profiles of the other three blocks, add more detailed information on functionally‐important haplotypes in Block 1 and 2 in the Japanese population, and identified differences in haplotype profiles between ethnic groups. Our updated analysis of ABCB1 haplotype blocks will assist pharmacogenetic and disease‐association studies carried out using Asian subjects.

Drug interaction between tacrolimus and carbamazepine in a Japanese heart transplant recipient: a case report.

This article reports changes in tacrolimus (FK506) blood levels connected with carbamazepine (CBZ). A drug interaction between FK506 and CBZ was investigated in a woman, who was in her 40s, who underwent heart transplantation. Pharmacokinetic parameters were measured, including dose and trough blood levels (C(0)), area under the serum concentration-time curve from 0 to 12 hours (AUC(0-12h)), and apparent clearance of oral FK506 (CL/F) for FK506 alone (about 3 months before starting CBZ) and combined with CBZ (11 days and about 3 months after starting CBZ). FK506 C(0) levels were decreased within 7 days of CBZ treatment. FK506 dosing required a 1.3- to 1.4-fold increase to maintain adequate blood levels while taking 200 mg CBZ daily. The AUC(0-12h)/dose 11 days after CBZ treatment was about 50% of the value before CBZ, and was about 70% at 3 months after CBZ treatment. The CL/F at 11 days and about 3 months after starting CBZ treatment was about 2 times higher than before CBZ therapy. FK506 C(0) levels are decreased by CBZ treatment, and blood levels should be closely monitored.

Drug interactions between tacrolimus and phenytoin in Japanese heart transplant recipients: 2 case reports.

OBJECTIVE The purpose of the study was to demonstrate how the interaction between phenytoin and tacrolimus (FK 506) can be managed clinically and to characterize the change in FK 506 levels after discontinuation of phenytoin in two Japanese heart transplant recipients with different dosing periods ofphenytoin. METHODS A drug interaction between phenytoin and FK 506 was investigated in 2 patients. The concentration-dose ratios (CDR: trough blood FK 506 level (ng/ml)/FK 506 dose (mg/day) on the previous day) were calculated as an index of the induction of the CYP3A4 enzyme during and after phenytoin therapy. RESULTS About 2- to 3-fold dosages of FK 506 were required to maintain the required blood level when phenytoin was used concomitantly in the two cases examined. The FK 506 dose was constant within 21 days after discontinuing phenytoin in Patient 1 who had 36 days of phenytoin therapy. In Patient 2 with 21-day phenytoin therapy, the FK 506 doses and CDR varied for 10 days after discontinuing phenytoin, and expected FK 506 C0 levels were achieved within 11 days. CONCLUSIONS The persistence of CYP induction after discontinuing phenytoin is dependent on the history of administration and, perhaps, on the dosing period in particular.