634 Background: Tamoxifen is a prodrug that is metabolized to active metabolites, Z-4-hydroxy-N-desmethyltamoxifen (BX) and Z-4-hydroxy-tamoxifen (4OH) where CYP2D6 plays a major role in the conversion. Genetic polymorphisms of CYP2D6 by ethnicities are well known with CYP2D6*10 in Asians (up to 50% in Koreans), and CYP2D6 *2 and *4 in American Whites as major variant alleles. We analyzed the steady state plasma concentrations of tamoxifen and its metabolites in patients (pts) with breast cancer to evaluate their associations with various CYP2D6 genotypes. Methods: Blood samples were collected from 219 pts on tamoxifen, 20 mg daily as adjuvant therapy for more than 3 months at National Cancer Center, Korea. Plasma tamoxifen, N-desmethyltamoxifen, BX, 4OH were measured by validated HPLC with fluorescence detector, and analyzed according to CYP2D6 genotype groups by Wilcoxon rank sum test. CYP2D6*10, CYP2D6*5 and CYP2D6*2×2 were identified by PCR-RFLP methods, and the rests were classified as CYP2D6*1 (wild type). This study was approved by IRB at National Cancer Center Hospital (NCCNHS04–033) and conducted after informed consent obtained by the patients. Results: Thus far, we measured plasma concentration of tamoxifen and its metabolites for 158 pts among 198 pts genotyped. 59 pts (29.8%) carried CYP2D6*1/*1, 84 pts (42.4%) *1/*10 and 49 pts (24.7%) *10/*10. Other types were CYP2D6*1/*5 (8.6%), *5/*5 (1.0%), *1/*2×2 (2.5%). Pts with CYP2D6 *10/*10 (n=40) demonstrated significantly lower steady state plasma concentrations of BX and 4OH than those with other genotypes (n=118) (BX: 7.9 vs.19.2. ng/ml [95 % CI; 5.5–10.4 vs. 15.8–22.7 ng/ml] p<0.0001; 4OH: 1.5 vs. 2.8 ng/ml [95 % CI; 1.1–2.0 vs. 2.3–3.3 ng/ml] p<0.0001), whereas there were no differences with *1/*10 (n=64) vs. without *10 allele (n=54) (BX: 20.6 vs. 18.1 ng/ml; 4OH: 2.9 vs. 2.7 ng/ml). Basically no significant differences in BX/4OH or other compounds by various CYP2D6*2 ×2 and *5 alleles were observed. Conclusions: The steady state plasma concentrations of BX and 4OH were significantly low with CYP2D6 *10/*10 genotype, and their clinical implications need to be explored.(Supported by a grant NCC-0410590). No significant financial relationships to disclose.
Steady-state plasma concentrations of haloperidol and reduced haloperidol after oral haloperidol in schizophrenic patients and analysis of factors determining their concentrations in hair.
