Comparative performance of oral midazolam clearance and plasma 4ß-hydroxycholesterol to explain interindividual variability in tacrolimus clearance.

ABSTRACT

AIMS: We compared the CYP3A4 metrics weight-corrected midazolam apparent oral clearance (MDZ Cl/F/W) and plasma 4ß-hydroxycholesterol/cholesterol (4ß-OHC/C) as they relate to tacrolimus (TAC) Cl/F/W in renal transplant recipients. METHODS: For a cohort of 147 patients, 8 h area under the curve (AUC) values for TAC and oral MDZ were calculated besides measurement of 4ß-OHC/C. A subgroup of 70 patients additionally underwent intravenous erythromycin breath test (EBT) and were administered the intravenous MDZ probe. All patients were genotyped for common polymorphisms in CYP3A4, CYP3A5 and P450 oxidoreductase, among others. RESULTS: MDZ Cl/F/W, 4ß-OHC/C/W, EBT and TAC Cl/F/W were all moderately correlated (r = 0.262-0.505). Neither MDZ Cl/F/W nor 4ß-OHC/C/W explained variability in TAC Cl/F/W in CYP3A5 expressors (n = 29). For CYP3A5 non-expressors (n = 118), factors explaining variability in TAC Cl/F/W in a MDZ-based model were MDZ Cl/F/W (R2  = 0.201), haematocrit (R2  = 0.139), TAC formulation (R2  = 0.107) and age (R2  = 0.032; total R2  = 0.479). In the 4ß-OHC/C/W-based model, predictors were 4ß-OHC/C/W (R2  = 0.196), haematocrit (R2  = 0.059) and age (R2  = 0.057; total R2  = 0.312). When genotype information was ignored, predictors of TAC Cl/F/W in the whole cohort were 4ß-OHC/C/W (R2  = 0.167), MDZ Cl/F/W (R2  = 0.045); Tac QD formulation (R2  = 0.036), and haematocrit (R2  = 0.032; total R2  = 0.315). 4ß-OHC/C/W, but not MDZ Cl/F/W, was higher in CYP3A5 expressors because it was higher in CYP3A4*1b carriers, which were almost all CYP3A5 expressors. CONCLUSIONS: A MDZ-based model explained more variability in TAC clearance in CYP3A5 non-expressors. However, 4ß-OHC/C/W was superior in a model in which no genotype information was available, likely because 4ß-OHC/C/W was influenced by the CYP3A4*1b polymorphism.