ABSTRACT
Pharmacokinetics considers the absorption, distribution, and elimination over time of a drug and its metabolites. Pharmacokinetic data consist of drug concentrations along with known sampling times and dosage regimens. A dosage regimen is defined by the route of administration and the sizes and timings of the doses. Population data arise when pharmacokinetic data are measured on a group of individuals, along with subject-specific covariates such as age, sex, or weight. Pharmacokinetic parameters of interest include the terminal half-life which is the time for the amount of drug to be halved in the “terminal phase,” and the apparent volume of distribution which relates the concentration to the total amount of absorbed drug. This is not a volume in the usual sense of the word, and it can be greater than body volume. The volume of blood (or plasma) which is cleared of drug per unit time is known as the clearance and is also a parameter of fundamental interest. The rate of elimination of the drug at any time is given by clearance multiplied by concentration. These parameters are useful for characterizing the drug and have traditionally been used to choose the dose and dosing interval that should be given to subjects in later phases of clinical development.
