Dietary phytochemicals and drugs: potential consequences of a common metabolism.

Dietary phytochemicals and prescription drugs are xenobiotics to human cells and are substrates of the same enzymes and transporters dedicated to biotransformation, detoxification and elimination. The interactions between phytochemicals and phase I and II biotransformation enzymes, as well as their systems of regulation, can often explain their known anticarcinogenic or antioxidant actions. However, for the same reason the contemporaneous intake of phytochemicals and drugs may result in the alteration of drug biodisposition and efficacy. In the present chapter the principal routes of biotransformation are described, as well as the mechanisms underlying their concerted regulation, and the biotransformation of the most significant phytochemicals is reported. Examples of phytochemicals/drugs interaction are illustrated and the importance of this issue for phytochemical supplementation is pointed out.