Pharmacogenetics 20/3/03. By Richard Twyman An introduction to the study of the genetic variations and drug response.

Genetic variability among humans has an obvious impact on features such as height, hair colour and appearance, but also has an unseen role in our susceptibility to disease and the way in which our bodies metabolise drugs.

This last area of study - termed pharmacogenetics - brings together the study of how drugs work in the body (pharmacology) and genetics. Understanding how genes can influence response to drugs can help explain some patients respond well to drugs and others do not. It can also help doctors understand why some patients require higher or lower doses of a particular drug.

The goal of pharmacogenetics research is to provide information for 'personalised medicine' - giving a patient the right medicine at the right dose.

A great deal of pharmacogenetics research has focused on the mechanisms that determine drug concentration within the body, looking at the end result of ingestion, absorption, metabolism, clearance and excretion of a drug. Genetic tests are being developed to determine a patient's ability to metabolise a particular drug, which will allow dosage to be determined with greater certainty, and also to determine which patients may be susceptible to adverse side effects as a result of being prescribed a drug.

The pharmacological consequences of genetic variation are highly diverse. In some cases, a patient may break down or convert a drug slightly more quickly, or slightly slower, than another. But in other cases, the absence of drug-metabolising enzymes can cause excessive, and fatal, drug action, or the therapy may fail because the drug is not activated.