Bioavailabilitet

Bioavailabilitet is a term used in pharmacology and toxicology to describe the fraction of an administered dose of an unchanged drug or active substance that reaches the systemic circulation. Essentially, it quantifies how much of a substance is absorbed into the bloodstream and becomes available to exert its intended effect. Several factors influence bioavailability, including the route of administration, the drug's chemical properties such as solubility and stability, and physiological factors of the individual like gastric emptying time and the presence of food.

For substances administered intravenously, bioavailability is considered 100% because the entire dose directly enters the systemic circulation. However, for other routes, like oral administration, bioavailability is typically less than 100%. This is due to processes such as incomplete absorption from the gastrointestinal tract, degradation by stomach acid or digestive enzymes, and first-pass metabolism in the liver, where a significant portion of the drug can be inactivated before it reaches the general circulation. Understanding bioavailability is crucial for determining appropriate dosages and predicting a drug's therapeutic efficacy and potential toxicity. Different formulations of the same drug can also exhibit varying bioavailability, impacting their effectiveness.