| Rabeprazole (RPZ), which is a relatively novel class of proton pump inhibitors (PPIs) after lansoprazole and pantoprazole, has been widely used for the treatment of acid-related diseases. It is metabolized mainly by cytochrome P450(CYP2C19). The activity of CYP2C19 depends on the CYP2C19 genotype status. This leads the marked kinetic difference of RPZ. Therefore, we studied the kinetic characteristics of RPZ in subjects who had different genotype status and intended to supply the basis of pharmacokinetics for the dose regimen of RPZ, based on identification of genotypes. Methods1. Genotyping procedures for CYP2C19: Venous blood samples (2ml each) were obtained from 70 unrelated healthy Chinese Han subjects. The proportion of men and women was 44/26. Their mean age was 22 years (range, 19~26 years). The genome DNA were extracted by classic SDS-proteinase K-hydroxybenzene-chloroform methods from blood. Though regular polymerase chain reaction (PCR) amplification, electrophoresis on 2% agarose gel and EB-staining, we observed and analyzed the specific segments of CYP2C19 ml in exon 5 and CYP2C19 m2 in exon 4, associated with the poor metabolizer phenotype. Using 50 bp DNA ladder as DNA marker in ultraviolet transilluminator. From these performances, the chosen good samples went on being digested with restriction endonuclear enzyme BamHI Sma □ separately. After electrophoresis on 4% agarose gel, took pictures using numeric camera and saved it in computer. We coded the bands in different number: 1 expressed wt/wt genotype type, 2 expressed wt/ml type, 3 expressed wt/m2 type, 4 expressed ml /ml type, 5 expressed ml/m2 type homozygote, 6 expressedm2/m2 type and inputted SPSS 10.0 to classify and analyze.2. The study for pharmacokinetics in subjects based on identification of genotypes: 18 unrelated healthy Chinese subjects were recruited from a total of 70 subjects. 6of them were homozygous for the wild-type(wt) allele in both exon 5 and exon 4(wt/wt) and classified as the homozygous extensive metabolizers (hoEMs) group.6 of them were classified as the heterozygous extensive metabolizers (heEMs) group. The other 6 of them were classified as the poor metabolizers (PMs) group. None of the subjects had a history of significant medical illness or being hypersensitive to any drugs. They did not consume extensive amounts of alcohol and were non-smokers. None of them had taken any other drugs for at least 2 weeks before the study and did not take any other drugs during the study. Their normal health status was judged on the basis of a physical examination with screening blood chemistries, including a complete blood count and liver function test, urinalysis and electrocardiogram performed before the study. After an overnight fast, each of them received an oral dose of 40mg rabeprazole as the enteric-coated formulation with 200ml water. A standardized meal was served separately at 4 hours and 10 hours after the drug ingestion. Venous blood samples (4ml each) were collected into heparinized tubes, immediately before the drug administration and at 1,2,3,4,5,6,7,8,10,12,15h after dosing. The samples were spun immediately after the collection, and the plasma samples were stored at -20 until assayed. . The plasma concentrations of rabeprazole were determined by reversed high-performance liquid chromatography(HPLC) with DAD detection according to an analytical method developed. The plasma concentration-time data were disposed with 3p97 program. The peak concentration (Cmax) and the peak time (Tmax) of rabeprazole were determined from the respective observed concentration-time data. The area under the curve (AUC) were calculated by the linear trapezoidal method. The data were expressed as mean values±SEM throughout the paper. Difference in pharmacokinetic data between the extensive metabolizer and poor metabolizer groups were evaluated statistically by use of a two-sample t test, p value of < 0.05 was considered to be statistically significant.Results1. Genotyping procedures for CYP2C19: Of the 70 individuals analyzed, 21were homozygous for the wild-type (wt) allele in both exon 5 and exon 4 (wt/wt), 31 were heterozygous for the CYP2C19 ml(wt/ml), 7 were heterozygous for the CYP2C19 m2(wt/m2), 3 were heterozygous for the two defects (ml/m2), and 8 were homozygous for the CYP2C19 ml(ml/ml). 11 were PMs phenotype, 21 were hoEMs phenotype and 38 were heterozygous extensive metabolizers (heEMs) phenotype. In healthy Chinese Han subjects, the allele frequencies of PMs, hoEMs, heEMs phenotype for CYP2C19 were 16°/ck 30%> 54%, respectively.2. The pharmacokinetics in subjects based on identification of genotype: The concentration-time curve in the hoEMs group ^ heEMs group and PMs group were adequately fit to one-compartment open model. The pharmacokinetic parameters such as AUC were (1454±294), (3208±789) and(6477±157) ug-h-I/1; ri/2ke were (0.90±0.12), (1.44±0.40)and(1.87±0.28) h; CL/F were (14.2±5.0), (5.8±2.2) and (1.6±0.7) mL-kg-'min"1 ; Cmax were (606.3±0.147.7) , (879.1±173.4) and (1421.0±372.7) ug/L ; 7max were (2.83±0.75), (3.17±0.75) and (3.33±1.03) h, respectively. As can be expected from the plasma concentration-time data, there were significant (p<0.05) genotype difference in the three groups in the mean kinetic parameters of rabeprazole such as AUC > Tm^ CL/F, Cmax.Conclusions1. CYP2C19-related genotype is one of the major factors to influence the interindividual kinetic variability of rabeprazole.2. There were marked differences in the metabolic disposition of rabeprazolebetween hoEMs group and heEMs group, hoEMs group and PMs group with respect to CYP2C19 from a China population: the poor metabolize group (PMs) -> the heterozygous extensive metabolize group(heEMs) had significantly greater AUC, Cmax and less CLorai of rabeprazole compared with the homozygous extensive metabolize group (hoEMs).3. We should take into account individualized dose regimen of rabeprazole,based on identification of genotype with respect to CYP2C19.
|
PDF Full Text Request