Population Pharmacokinetic Analysis of Tacrolimus in Adult Chinese Patients with Myasthenia Gravis: A Prospective Study.

BACKGROUND AND OBJECTIVES

Tacrolimus is a widely used immunosuppressive agent with narrow therapeutic window. Nowadays, tacrolimus has gained acceptance as a therapeutic option in myasthenia gravis (MG) treament, however, little is known about its pharmacokinetic characteristics in MG population. In this study, we aimed to investigate the population pharmacokinetic (PopPK) of tacrolimus in patients with MG and to develop model-informed dosing regimens.

METHODS

Trough concentrations of tacrolimus (267 measurements) and cytochrome P450 (CYP) genotypes were determined in 97 Chinese adults. The non-linear mixed-effects model was used for PopPK modeling. Monte Carlo simulations based on the established model were employed to design dosing regimens.

RESULTS

The PopPK model was described using a one-compartment model with first-order absorption and elimination. The mean apparent clearance (CL/F) of tacrolimus was 17.1 L/h, with a between-subject variability of 20.1%. Covariate screening of demographic characteristics, blood test results, co-medications, and CYP3A53 or CYP3A41G polymorphisms showed that the CYP3A5*3 genotype and co-administration of a Wuzhi capsule significantly affected tacrolimus CL/F.

CONCLUSIONS

For patients with the CYP3A533 allele, the required tacrolimus dose for 75% of subjects to achieve target trough concentrations of 4.8-15 ng/mL was 2 mg every 12 h (q12h). For patients with the CYP3A511 allele, the required dose was 2 mg tacrolimus q12h with a Wuzhi capsule, and for patients with the CYP3A513 allele, the required dose was 3 mg of tacrolimus q12h or 4 mg q24h co-administered with a Wuzhi capsule. This model could be employed to optimize individualized therapies for patients with MG.