Half-Life Definition

The length of time it takes for the body to metabolize or eliminate from the body 50 percent of the amount of a drug a person takes or receives. Drug half-life is an important factor in determining appropriate dosage and for treating overdose. Drug half-life also helps the doctor know when to expect to begin to see the effects of the drug. The calculation of drug half-life is logarithmic.

Drug informational literature, packaged with prescription drugs, provides general information about the drug’s half-life that is generally adequate for most clinical circumstances. A doctor may conduct blood tests to measure the levels of a drug in an individual’s blood circulation over a period of time as a means of indirectly assessing half-life, though this is seldom therapeutically necessary.

See also BIOAVAILABILITY; CYTOCHROME P450 (CYP450) ENZYMES; EFFICACY; METABOLISM; PEAK LEVEL; THERAPEUTIC LEVEL; THERAPEUTIC WINDOW; TROUGH LEVEL.

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