Pharmacology: Bioavailability

Introduction

Drug Properties

Physiology

Medicine Properties

Bioavailability

Activity

Assessment

Resources

Introduction

Drugs are administered by various routes and in most cases reach the site of action via the systemic circulation. If a drug is injected intravenously, the total amount is immediately available to exert a therapeutic effect

The same is not true of other routes. Let's take the oral route as an example. How does a drug taken orally reach the systemic circulation? Once swallowed it quickly reaches the stomach where it dissolves and some of it may be absorbed. Absorption is completed in the small intestine.

From here it travels to the hepatic portal vein before reaching the systemic circulation via the hepatic vein. What could prevent some of the drug from reaching the systemic circulation? There are many factors but they can be grouped into three:

1st) The properties of the drug

2nd) Important physiological factors

3rd) The properties of the medicine

Now please move on to the next section were we will discuss the first of these factors.