Relative contributions of metabolic enzymes to systemic elimination can be estimated from clinical DDI studies: Validation using an in silico approach.

OBJECTIVE: The contribution ratios (CR) of metabolic enzymes to the systemic clearance of a drug can be estimated from in vitro studies. Another feasible approach is to calculate them based on the increase in the area under the time-concentration curve (AUC) caused by the co-administration of a potent and selective inhibitor in a clinical drug-drug interaction (DDI) study. However, some factors, such as the inhibitory potency of the inhibitor and the inhibition of first-pass metabolism, might affect the estimation of CR based on clinical DDI studies. We aimed to validate the accuracy of the DDI-based estimation of CR using an in silico approach. MATERIALS AND METHODS: An in silico DDI study was conducted using a population-based physiological pharmacokinetic simulator to estimate the CR of cytochrome P450 (CYP)3A4 for zolpidem, sildenafil, omeprazole, triazolam, and repaglinide. The ratio of the AUC value seen in the presence of an inhibitor (ketoconazole or itraconazole) to that observed in the absence of the inhibitor (AUC ratio) was also calculated. The CR for CYP3A4 obtained using the simulator (CRdef) were compared with those calculated from the AUC ratio (CRest). RESULTS: When ketoconazole was used, good correlations between the CRest and CRdef were obtained for all examined substrates (inconsistencies were seen in < 10% of subjects). CR estimates derived from the AUC ratio were found to be accurate. Some underestimation was observed, possibly due to incomplete inhibition, and some overestimation caused by extensive first-pass metabolism was noted. CONCLUSION: This study verified that CR obtained from AUC ratios in DDI studies are quite reliable.

A case of long-term dasatinib-induced proteinuria and glomerular injury.

A 52-year-old woman was diagnosed with chronic myeloid leukemia. Treatment with dasatinib, a second-generation Bcr-Abl tyrosine kinase inhibitor, was initiated, and complete cytogenetic remission was achieved. Two years later, proteinuria occurred, and the urinary protein level increased gradually in the next 3 years. Moreover, the serum creatinine level increased mildly during this period. The urinary protein level reached 2.18 g/gCr; hence, a renal biopsy was conducted. Light microscopy revealed mild proliferation of mesangial cells, and immunofluorescence analysis revealed IgG and C3 depositions in the mesangial area. Electron microscopy revealed electron-dense deposition in the paramesangial area, partial podocyte foot process effacement, and segmental endothelial cell swelling with a slight expansion of the subendothelial space. Dasatinib was discontinued, and within 3 weeks, the proteinuria disappeared, with improvements in her renal function. After switching to bosutinib, a new second-generation of tyrosine kinase inhibitor, the proteinuria remained negative. The rapid cessation of proteinuria following dasatinib discontinuation indicated that proteinuria was induced by the long-term administration of dasatinib. Proteinuria and renal function should be regularly monitored during dasatinib therapy.

Hepatitis E during Tocilizumab Therapy in a Patient with Rheumatoid Arthritis: Case Report and Literature Review.

Hepatitis E is an acute self-limiting disease caused by hepatitis E virus (HEV). Recent reports show that HEV can induce chronic hepatitis or be reactivated in immunocompromised hosts. We report a 63-year-old woman with rheumatoid arthritis (RA) who developed hepatitis E during treatment with tocilizumab. Analysis of serially stocked serum samples confirmed that hepatitis was caused by primary infection with HEV and not by viral reactivation. Her liver function improved after discontinuing tocilizumab and remained within the normal range without reactivation of HEV for >5 years after restarting tocilizumab. We also reviewed the published cases of hepatitis E that developed during RA treatment.