Purpose: To assess the possibility of using CYP2D6 10 +/- CYP3A5*3 as biomarkers to predict the pharmacokinetics of diltiazem and its two metabolites among healthy Chinese subjects. METHODS 41 healthy Chinese were genotyped for CYP3A5 3 and CYP2D6 10, and then received a single oral dose of diltiazem hydrochloride capsules (300 mg). Multiple blood samples were collected over 48 h, and the plasma concentrations of diltiazem, N-desmethyl diltiazem and desacetyl diltiazem were determined by HPLC-MS/MS. The relationships between the genotypes and pharmacokinetics were investigated.
Results: The pharmacokinetics of diltiazem, N-desmethyl diltiazem were not significantly affected by both CYP3A5 3 and CYP2D6*10 alleles. However, the systemic exposure of the pharmacologyically active metabolites, desacetyl diltiazem, was 2-fold higher in CYP2D6 10/10 genotype carriers than in 1/10 or 1/1 ones (AUC(o-inf) of CYP2D6 1/1, 1/10 and 10/10 are 398.2 +/- 162.9, 371,0 69.2 and 726.2 +/- 468.1 respectively, p <0.05).
Conclusions: Two of the most frequent alleles, CYP3A5 3 and CYP2D6 10, among Chinese do not have major impacts on the disposition of diltiazem and N-desmethyl diltiazem. However, the desacetyl diltiazem showed 2-fold accumulation in individuals with CYP2D6 10/10 genotype. Despite this, the effect of genotype of CYP2D6 on clinical outcome of diltiazem treatment is expected to be limited.