Medicina

Our tissues are exposed on a daily basis to xenobiotic- foreign substances that are not naturally found in the body.
Most drugs are xenobiotic that are used to modulate bodily functions fortherapeutic ends, drugs and other environmental chemicals that enter the body are modified by a vast array of enzymes.
The biochemical transformations performed by a vast array of enzymes can alter thecompound to render in beneficial, harmful, or simply ineffective. The processes by which biochemical reactions alter drugs within the body are collectively called drug metabolism or drugbiotransformation.
The previous chapter introduced the importance of renal clearance in the pharmacokinetics of drugs. Although the biochemical reactions that alter drugs to renally excretable forms are an essentialpart of drug metabolism, drug biotransformation can alter drugs in four important ways:

An active drug may be converted to an inactive drug.
An active drug may be converted to an active or toxicmetabolite
An inactive prodrug may be converted to an active drug
An unexcretable drug may be converted to an excretable metabolite (e.g to enhance renal or biliary clearance)

This chapterpresents the major processes of drug metabolism. Following the case is an overview of sites of drug metabolism, focusing principally, on the liver. The two major types of biotransformation are thediscussed: these are often termed phase I and phase II reactions. Although the terminology is imprecise and it incorrectly implies a temporal order of the reactions. (In addition, “phase III” is sometimesused to describe the process of drug transport which is even more confusing) in this chapter we use “oxidation/ reduction” and “conjugation/ hydrolysis” to describe these processes more accurately.The chapter concludes with a discussion of the factors that can lead to differences in drug metabolism among individuals.

SITES OF DRUG METABOLISM
THE LIVER IS THE MAIN ORGAN OF DRUG METABOLISM....