Elimination Half-Life

Synonyms

Biological half-life; Terminal half-life

Definition

The plasma half-life of a drug (t½) is the time necessary to reduce the plasma concentration by half, for example, to decrease from 100 to 50 mg/L. The knowledge of the half-life is useful for the determination of the frequency of administration of a drug (the number of intakes per day) for obtaining the desired plasma concentration. Generally, the half-life of a particular drug is independent of the dose administered. In certain exceptional cases, it varies with the dose: it can increase or decrease according to, for example, the saturation of a mechanism (elimination, binding to plasma proteins, etc.).

Cross-References

• Area Under the Curve

• Bioavailability

• First-Order Elimination Kinetics

• Pharmacokinetics