ABCB1 polymorphisms may have a minor effect on ciclosporin blood concentrations in myasthenia gravis patients

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Numerous studies have shown that MDR1 polymorphisms in the form of single nucleotide poymorphisms or haplptype affect ciclosporin pharmacokinetics or blood concentrations in organ transplantation patients, but some results conflict with others. WHAT THIS STUDY ADDS • We had thought that the diease condition might conceal the minor effect of MDR1 polymorphisms. • We chose myasthenia gravis patients as a population in which disease conditions were less severe. • We also used different pharmacokinetics indices, such as dose‐adjusted trough blood concentrations, dose‐adjusted peak blood concentrations and trough blood concentrations under the same ciclosporin regimen. AIMS Ciclosporin (CsA), which is widely used in autoimmune disease and transplantation, has a narrow therapeutic index. It also shows considerable interindividual variability in its pharmacokinetics, which may be attributable to polymorphisms of the multidrug efflux pump P‐glycoprotein, encoded by MDR‐1. The aim was to determine the role of genetic polymorphisms in MDR‐1 with respect to interindividual variability of CsA blood concentrations in myasthenia gravis (MG) patients. METHODS MG patients (n = 129) receiving CsA were genotyped for MDR‐1 1236C→T (exon 12), 2677G→T (exon 21) and 3435C→T (exon 26). Trough blood and peak blood concentrations were determined to see if there was correlation with the corresponding genotype. RESULTS We observed a trend for CsA blood concentrations, especially peak blood concentrations, to be higher with the wild‐type allele compared with minor alleles in genotype and haplotype. Furthermore, under the same CsA regimen, it was found that the trough concentrations of variant genotype (ABCB1 1236TT or ABCB1 2677TT) were significant greater than those of wild‐type (ABCB1 1236CC or ABCB1 2677GG, respectively) (P = 0.0222 and 0.0081). The trough concentrations of wild‐type haplotype pair group were significantly lower those that of the mutant type pair group (TT‐TT‐TT) (P = 0.007). CONCLUSIONS ABCB1 polymorphisms in both genotype and haplotype may have a minor effect on the CsA blood concentrations.