What is bioavailability?

Bioavailability refers to the proportion of an administered drug that reaches systemic circulation in an unchanged form, making it available for therapeutic action. It is a critical aspect of pharmacokinetics because it determines the extent and rate at which the active ingredient or active moiety is absorbed and becomes available at the site of action.

When a drug is administered, its bioavailability plays a crucial role in ensuring that sufficient amounts reach the bloodstream to achieve the desired pharmacological effect. This concept is particularly important in understanding how different routes of administration (e.g., intravenous, oral, subcutaneous) can affect the absorption and ultimately the therapeutic effectiveness of a medication.

The total amount of drug administered does not account for how much actually enters circulation, which is why it is not a correct definition of bioavailability. Additionally, while the rate of absorption and the drug’s effectiveness at the target site are related concepts, they do not fully encapsulate what bioavailability measures. Bioavailability specifically emphasizes the proportion reaching systemic circulation rather than just the absorption rate or effectiveness at the action site.