Recent advances: the cytochrome P450 enzymes.

Successful application of information on cytochrome P450 to prevent drug interactions and improve the therapeutic risk: benefit ratio can occur only if we know which enzyme is responsible for the metabolism of a drug. Until recently, this information was not usually available when new drugs reached the market. It is not enough to know the fraction of a dose metabolized versus excreted unchanged or the metabolic pathways by which a compound is degraded. Studies conducted during drug development must identify the enzyme or enzymes involved in the metabolism of new drugs. In addition, the ability of new drugs to inhibit or induce the activity of the key P450 enzymes must be known if we are to take full advantage of our current knowledge of how the cytochrome P450 system works.