The term pharmacokinetics is derived from the ancient Greek words “pharmakon” and “kinetikos”, meaning “drug” and “putting in motion” respectively. It is one of the main branches of pharmacology, and refers to the way that the body reacts on and affects a pharmaceutical substance in the body.
From the moment that a drug enters the body, the body recognizes it and processes it in a unique way, according to the individual characteristics of the drug. Pharmacokinetics is the study of how the body reacts to the presence of the drug. This information can be used to improve the administration and use of medicines.
There are four main components of pharmacokinetics: liberation, absorption, distribution, metabolism and excretion (LADME). These are used to explain the various characteristics of different drugs in the body. They are covered in more detail below.
Liberation is the process in which a pharmaceutical substance is released from the formulation it is delivered in. This must occur before the drug can be absorbed into the body.
Absorption is the process in which a pharmaceutical substance enters the blood circulation in the body. The pharmacokinetic parameters for absorption include:
- Absorption rate constant: absorption rate / amount of drug remaining to be absorbed
- Bioavailability: amount of drug absorbed / drug dose
Distribution is the process in which a pharmaceutical substance is dispersed through the fluids and tissues in the body. The pharmacokinetic parameters for distribution include:
- Apparent volume of distribution: amount of drug in body / drug concentration in plasma
- Unbound fraction: unbound drug concentration in plasma / total drug concentration in plasma
Metabolism is the process in which a pharmaceutical substance is transformed into other substances, called metabolites, in the body. The pharmacokinetic parameters for metabolism include:null
- Metabolic clearance: drug metabolism rate / drug concentration in plasma