ru-66647 and nefazodone

The clinical impact of drug-drug interactions based on time-dependent inhibition of cytochrome P450 (CYP) 3A4 has often been overpredicted, likely due to use of improper inhibitor concentration estimates at the enzyme. Here, we investigated if use of cytosolic unbound inhibitor concentrations could improve predictions of time-dependent drug-drug interactions. First, we assessed the inhibitory effects of ten time-dependent CYP3A inhibitors on midazolam 1'-hydroxylation in human liver microsomes. Then, using a novel method, we determined the cytosolic bioavailability of the inhibitors in human hepatocytes, and used the obtained values to calculate their concentrations at the active site of the enzyme, i.e. the cytosolic unbound concentrations. Finally, we combined the data in mechanistic static predictions, by considering different combinations of inhibitor concentrations in intestine and liver, including hepatic concentrations corrected for cytosolic bioavailability. The results were then compared to clinical data. Compared to no correction, correction for cytosolic bioavailability resulted in higher accuracy and precision, generally in line with those obtained by more demanding modelling. The best predictions were obtained when the inhibition of hepatic CYP3A was based on unbound maximal inhibitor concentrations corrected for cytosolic bioavailability. Our findings suggest that cytosolic unbound inhibitor concentrations improves predictions of time-dependent drug-drug interactions for CYP3A.

Topics: Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inhibitors; Cytosol; Drug Interactions; Humans; Ketolides; Kinetics; Microsomes, Liver; Pharmaceutical Preparations; Piperazines; Triazoles

Idiosyncratic drug-induced hepatotoxicity accounts for about 13% of all cases of acute liver failure, therefore cited as the most frequent reason for post-marketing drug withdrawal. Despite this, the underlying mechanisms remain poorly understood due to lack in adequate screening assays and predictive in vitro models. Hepatic transporters play a crucial role in the absorption, distribution, and elimination of both endogenous substrates and xenobiotics. Defects in transporter function can lead to altered drug disposition, including toxicity and loss of efficacy. Inflammation is one condition for demonstrated variable drug response, attributed in part, to changes in function of drug transporters. The present study investigates the implication of two important hepatic transporters (MDR1 and MRP2) in idiosyncratic drug-induced hepatotoxicity in the presence and absence of an inflammatory context. The synergistic effect of idiosyncratic drugs (Trovafloxacin, nimesulide, telithromycin, and nefazodone) and inflammatory stimuli (TNF-α + LPS) on the efflux activity of hepatic transporters was studied using microvolume cytometry. Our results demonstrated on the one hand that both MDR1 and MRP2 are variably implicated in idiosyncratic drug-induced liver injury and on the other hand that the occurrence of an inflammatory reaction during idiosyncratic drug therapy can noticeably modulate this implication. In the absence of an inflammatory stress, none of the four tested drugs modulated the efflux activity of MRP2; nevertheless telithromycin and nefazodone inhibited the efflux activity of MDR1. Upon occurrence of an inflammatory stress, the inhibitory potential of trovafloxacin, nimesulide, and nefazodone on the efflux activity of MRP2 was noticeably revealed, while the telithromycin and nefazodone-induced inhibition of MDR1 was clearly attenuated. Knowledge of underlying mechanisms may significantly contribute to elimination of potential hepatotoxic drugs long before marketing and to prevention of drug-induced hepatotoxicity.

Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP-Binding Cassette Sub-Family B Member 4; Biological Transport; Chemical and Drug Induced Liver Injury; Flow Cytometry; Fluoroquinolones; Gene Expression Regulation; Hep G2 Cells; Hepatocytes; Humans; Inflammation; Ketolides; Lipopolysaccharides; Liver; Naphthyridines; Piperazines; Sulfonamides; Triazoles; Tumor Necrosis Factor-alpha; Xenobiotics