Biological half life

Biological half-life or elimination half-life is the time it takes for a substance (drug, radioactive nuclide, or other) to lose one-half of its pharmacologic, physiologic, or radiological activity. In a medical context, the half-life may also describe the time that it takes for the concentration in blood plasma of a substance to reach one-half of its steady-state value (the "plasma half-life").

Pharmacokinetics

Pharmacokinetics is the study of how an organism affects a drug, in terms of absorption, distribution, metabolism, and excretion (ADME). The biological half-life is an important pharmacokinetic parameter and it changes with age, kidney function, and comorbidities.

Calculation

The biological half-life of a biological substance may be affected by several factors, including its rate of absorption, distribution metabolism, and excretion. These factors can affect the rate at which a substance is eliminated from the body, and thus its biological half-life.

Factors affecting biological half-life

Several factors can affect the biological half-life of substances. These include the individual's metabolic rate, the substance's solubility, its distribution within the body, various genetic factors, the method of administration, and the age and sex of the individual.

Clinical significance

The biological half-life of a substance can have significant implications for the management of poisoning or drug overdose. For example, substances with a short half-life will be rapidly eliminated from the body, while substances with a long half-life may require more intensive and prolonged treatment.

See also

• Pharmacodynamics
• Pharmacology
• Toxicology