Table of Contents
1.1.1 Pharmcokinetics and Toxicokinetics
Describes the movement of drugs into, around and out of the body.
This movement is dependent upon the characteristics of the individual drugs and the various processes that eliminate the drugs. This movement is often described by graphing drug concentrations (most commonly blood concentrations) against time. The changes in blood concentration can also be described with mathematical formulae.
Describes the effects that drugs have on the body or specific organs.
The terms toxicokinetics and toxicodynamics are often used as an abbreviation for “pharmacokinetics in overdose” and for “pharmacodynamics in overdose”.
Absorption, Distribution, Metabolism and Elimination
After a drug or chemical is swallowed it must be dissolved then move across a gastrointestinal membrane which is charged phospholipid structure. It will then be transported (with a variable amount attached to blood proteins) in the portal blood stream to the liver where it may undergo a variable amount of metabolism before it eventually enters the systemic circulation. Once it enters the systemic circulation it is distributed into different areas of the body. The concentrations of drug may differ in different organs of the body. During and after distribution the drug may produce effects by either binding to specific receptors or by having direct effects on tissues. The drug continues to be eliminated, most commonly by hepatic metabolism and renal excretion. There is considerable genetic variation for many of these processes in particular including drug transporters, metabolic enzymes and receptor binding.
When the mechanisms of drug handling are all being utilised to their maximum activity they are commonly described as being saturated. This occurs with relatively few drugs in therapeutic concentrations but is substantially more common following overdose. It is an important concept because, once it occurs, the usually described pharmacokinetics of a drug (from therapeutic use) change.
- 188.8.131.52 Models (eg. compartmental, physiologic)