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 excreted. 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 prodrugs, 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 accumulation of drugs when they’re given together. This accumulation increases the potential for an adverse reaction or drug toxicity.

Conditional considerations

Certain diseases can reduce metabolism. These include liver diseases such as cirrhosis as well as heart failure, which reduces circulation to the liver.

Gene machine

Genetics allows some people to metabolize drugs rapidly and others to metabolize them more slowly.

Stress test

Environment, too, can alter drug metabolism. For example, cigarette 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 instance, infants have immature livers that reduce the rate of metabolism, and elderly patients experience a decline in liver size, blood flow, and enzyme production that also slows metabolism.