Metabolism is one of the major routes of eliminating a drug from the body. For most drugs, only a few enzymes mediate the metabolic pathways; therefore, coadministration of drugs can potentially lead to metabolism-based DDIs. Thus, the assessment of drug interactions in the drug discovery phase, as well as in the clinic, is a necessary part of providing safe and effective drugs to the market. Many parameters are involved in this assessment, taking into consideration the role of each drug as either a victim (i.e., substrate or object) or a perpetrator (i.e., inhibitor or precipitant). For each situation, different questions need to be addressed.
For the victim (object, substrate), we need to know the contribution of various elimination pathways, the kinetic parameters for the affected pathway, the extent of plasma protein binding, and the drug concentration at the enzyme site.
For the perpetrator (inhibitor), we need to know the mechanism of inhibition, the inhibitory properties of the compound, the extent of plasma protein binding, and the inhibitor concentration at the enzyme site.
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