Those metabolic reactions involved in the uptake, modification and elimination of chemical compounds that are foreign to the biological system. This includes the biotransformation pathways organisms use to detoxify the system and the degradation of toxic pollutants by microorganisms. Many of the compounds that enter the cell are inactive and the transformation pathways aim to increase their hydrophilicity and ease elimination. In the process, some of the intermediates may give rise to toxic metabolites and effects. The transformation pathways are also important for the pharmacokinetics aspect of drug metabolism. The distinction is that a drug is a foreign compound intentionally administered. In the case of the degradation pathway, microoganismal enzymes have the ability to degrade otherwise resistant compounds.