The Principles of Drug Action

The effect that a drug has depends upon a number of different factors. Among these are the mode of administration, the way in which the drug is metabolized and the speed at which it is broken down and excreted. Drugs are usually administered through one of three methods; oral, intravenous or intramuscular. Other routes include subcutaneous and intraperitoneal but these are less frequently used. Intravenous administration tends to have the fastest action and oral administration the slowest. This is because drugs taken orally have to be absorbed from the gut before they can act. Some drugs are metabolized by the body very quickly whereas other drugs are metabolized more slowly. Some drugs are better at having their desired effect than others. The relationship between the dose of drug and the effect observed is called the doseresponse function. For some drugs, there is an optimal dose range that has therapeutic effects. This range is called the therapeutic window.