Notes on xenobiotic metabolism

There is no doubt that the advent of sensitive analytical techniques that have made possible quantitative studies of xenobiotic kinetics and metabolism has opened new perspectives in interpreting the biological and toxicological effects of xenobiotics. However reliance on concentrations of the xenobiotic under investigation and on precise knowledge of xenobiotic metabolic pathways rather than on doses is not yet widespread. Similarly precise information about concentrations and biotransformation of xenobiotics is necessary when working with cellular systems. Only an integrated approach taking into consideration in vitro and in vivo differences as well as differences between animal species offers a rational basis for extrapolating data from animals to man. Despite limited success in interpreting the toxic effects of some chemicals, we still lack the understanding of toxicological mechanisms essential for any extrapolation. The prediction of toxicological effects of xenobiotics must therefore be considered an open field of investigation where cross-fertilization among various approaches and disciplines is the best hope for obtaining sounder results.