Pharmacokinetics: Metabolism

Metabolism

Drug metabolism, or biotransformation, is the process by which the body changes a drug from its dosage form to a more water-soluble form that can then be excret-ed. Drugs can be metabolized in several ways:

·                 Most drugs are metabolized into inactive metabolites (products of metabolism), which are then excreted.

·                 Other drugs are converted to active metabolites, which are capable of exerting their own pharmacologic action. Active metabolites may undergo further metabolism or may be excreted from the body unchanged.

·                 Some drugs can be administered as inactive drugs, called pro-drugs, which don’t become active until they’re metabolized.

Where metabolism happens

The majority of drugs are metabolized by enzymes in the liver; however, metabolism can also occur in the plasma, kidneys, and membranes of the intestines. In contrast, some drugs inhibit or compete for enzyme metabolism, which can cause the accumula-tion of drugs when they’re given together. This accumulation in-creases the potential for an adverse reaction or drug toxicity.

Conditional considerations

Certain diseases can reduce metabolism. These include liver dis-eases such as cirrhosis as well as heart failure, which reduces cir-culation to the liver.

Gene machine

Genetics allows some people to metabolize drugs rapidly and oth-ers to metabolize them more slowly.

Stress test

Environment, too, can alter drug metabolism. For example, ciga-rette smoke may affect the rate of metabolism of some drugs; a stressful situation or event, such as prolonged illness, surgery, or injury, can also change how a person metabolizes drugs.

The age game

Developmental changes can also affect drug metabolism. For in-stance, infants have immature livers that reduce the rate of metab-olism, and elderly patients experience a decline in liver size, blood flow, and enzyme production that also slows metabolism.