Plasma half-life

Plasma half-life is a term used in pharmacokinetics and toxicology to describe the period of time it takes for the concentration of a substance in the plasma to reduce by half. This concept is crucial in understanding the dynamics of drug elimination and dosage.

Definition

The plasma half-life of a drug or other substance is the time required for its concentration in the plasma to decrease by half. This is a key parameter in pharmacokinetics, as it influences the duration of drug action and the dosing interval for repeated administration.

Determination

The plasma half-life of a substance can be determined through various methods. One common method is through blood sampling and subsequent laboratory analysis. The concentration of the substance in the plasma is measured at various time points after administration, and the half-life is calculated using mathematical models.

Factors Influencing Plasma Half-Life

Several factors can influence the plasma half-life of a substance. These include the rate of metabolism, the rate of excretion, and the volume of distribution. Changes in these factors can lead to significant variations in plasma half-life, which can in turn affect the pharmacological effects of the substance.

Clinical Significance

Understanding the plasma half-life of a drug is crucial in clinical practice. It helps in determining the dosing interval for a drug, and in predicting the time it takes for a drug to be eliminated from the body. This information is particularly important in the management of drug overdose and in the adjustment of drug therapy in patients with impaired renal or hepatic function.

See Also

• Pharmacokinetics
• Volume of distribution
• Drug metabolism
• Drug excretion