CYP3A4 drug interactions: correlation of 10 in vitro probe substrates

Aims Many substrates of cytochrome P450 (CYP) 3A4 are used for in vitro inv estigations of drug metabolism and potential drug-drug interactions. The ai m of the present study was to determine the relationship between 10 commonl y used CYP3A4 probes using modifiers with a range of inhibitory potency. Methods The effects of 34 compounds on CYP3A4-mediated metabolism were inve stigated in a recombinant CYP3A4 expression system. Inhibition of erythromy cin, dextromethorphan and diazepam N-demethylation, testosterone 6 beta-hyd roxylation, midazolam 1-hydroxylation, triazolam 4-hydroxylation, nifedipin e oxidation, cyclosporin oxidation, terfenadine C-hydroxylation and N-dealk ylation and benzyloxyresorufin O-dealkylation was evaluated at the apparent K-m or S-50 (for substrates showing sigmoidicity) value for each substrate and at an inhibitor concentration of 30 mu M. Results While all CYP3A4 probe substrates demonstrate some degree of simila rity, examination of the coefficients of determination, together with diffe rence and cluster analysis highlighted that seven substrates can be categor ized into two distinct substrate groups. Erythromycin, cyclosporin and test osterone form the most closely related group and dextromethorphan, diazepam , midazolam and triazolam form a second,group. Terfenadine can be equally w ell placed in either group, while nifedipine shows a distinctly different r elationship. Benzyloxyresorufin shows the weakest correlation with all the other CYP3A4 probes. Modifiers that caused negligible inhibition or potent inhibition are generally comparable in all assays, however, the greatest va riability is apparent with compounds causing, on average, intermediate inhi bition. Modifiers of this type may cause substantial inhibition, no effect or even activation depending on the substrate employed. Conclusions It is recommended that multiple CYP3A4 probes, representing eac h substrate group, are used for the in vitro assessment of CYP3A4-mediated drug interactions.