The pharmacokinetics of many drugs are altered by pregnancy. Drug distribution and protein binding are changed by pregnancy. While some drug metabolizing enzymes have an apparent increase in activity, others have an apparent decrease in activity. Not only is drug metabolism affected by pregnancy, but renal filtration is also increased. In addition, pregnancy alters the apparent activities of multiple drug transporters resulting in changes in the net renal secretion of drugs.

We evaluated the hypothesis that CYP3A5 expression can affect intrarenal tacrolimus accumulation. An oral dose of tacrolimus was administered to 24 healthy volunteers who were selected based on their CYP3A5 genotype. Compared to CYP3A5 nonexpressors, expressors had a 1.6-fold higher oral tacrolimus clearance and 2.0- to 2.7-fold higher metabolite/parent AUC ratios for 31-DMT, 12-HT and 13-DMT. In addition, the apparent urinary tacrolimus clearance was 36% lower in CYP3A5 expressors, compared to nonexpressors. To explore the mechanism behind this observation, we developed a semi-physiological model of renal tacrolimus disposition and predicted that tacrolimus exposure in the renal epithelium of CYP3A5 expressors is 53% of that for CYP3A5 nonexpressors, when normalized to blood AUC. These data suggest that at steady state, intrarenal accumulation of tacrolimus, and its primary metabolites, will depend on the CYP3A5 genotype of the liver and kidneys. This may contribute to inter-patient differences in the risk of tacrolimus-induced nephrotoxicity.

Background Higher concentrations of AM19 and AM1c9, secondary metabolites of cyclosporine A (CsA), have been associated with nephrotoxicity in organ transplant patients. The risk of renal toxicity may depend upon the accumulation of CsA and its metabolites in the renal tissue. We evaluated the hypothesis that CYP3A5 genotype, and inferred enzyme expression, affects systemic CsA metabolite exposure and intra-renal CsA accumulation. Methods An oral dose of CsA was administered to 24 healthy volunteers who were selected based on their CYP3A5 genotype. CsA and its six main metabolites in whole blood and urine were measured by LC-MS. In vitro incubations of CsA, AM1, AM9 and AM1c with recombinant CYP3A4 and CYP3A5 were performed to evaluate the formation pathways of AM19 and AM1c9. Results The mean CsA oral clearance was similar between CYP3A5 expressors and nonexpressors. However, compared to CYP3A5 nonexpressors, the average blood AUC for AM19 and AM1c9 was 47.4% and 51.3% higher in CYP3A5 expressors (P = 0.040 and 0.011, respectively), corresponding to 30% higher AUCmetabolite/AUCCsA ratios for AM19 and AM1c9 in CYP3A5 expressors. The mean apparent urinary CsA clearance, based on a 48-hour collection, was 20.4% lower in CYP3A5 expressors compared to CYP3A5 nonexpressors (4.2 ± 1.0 and 5.3 ± 1.3 mL/min, respectively, P = 0.037), which is suggestive of CYP3A5-dependent intra-renal CsA metabolism. Conclusions At steady-state, intra-renal accumulation of CsA and its secondary metabolites should depend on the CYP3A5 genotype of the liver and kidneys. This may contribute to inter-patient variability in the risk of CsA-induced nephrotoxicity.