The term bioavailability describes how much of a nutrient or active ingredient can be absorbed and utilized by an organism.

Bioavailability is a measure of how well your body absorbs a medicine. It tells you how quickly and efficiently your body processes a substance, and it is important to know because it is one of the main factors that determines how much of a medicine you need to take to achieve the desired effect.

Bioavailability is comparable to absorption: it is the proportion of an active substance that is available unchanged in the bloodstream. It indicates how quickly and to what extent the substance (usually a drug) is absorbed (resorbed) and is available unchanged at the site of action.

The bioavailability after intravenous administration (by definition 100%, red, i.v.) and after oral administration (black, gray, p.o.): If the areas under the curves for the time period are the same for both modes of administration, the oral bioavailability also corresponds to 100% (gray area under black curve). Smaller areas correspond to lower bioavailability.

What is the definition of bioavailability?

Bioavailability is a measure of how well a medicine can be absorbed by the body. It is usually expressed as a percentage and is important because it can affect how much medication you need to take and how your body reacts to the medication.

There are different ways to measure bioavailability: absolute bioavailability, relative bioavailability and oral bioavailability.

Absolute bioavailability refers to the amount of active ingredients in a dosage form in relation to their concentration in plasma after intravenous administration. This means that intravenously administered drugs always have an absolute bioavailability of 100 percent.

Relative bioavailability compares one dosage form to another dosage form that is considered standard (e.g. a tablet to a solution). For example, if you change an orally administered medication to an injection, your doctor will want to know whether or not this change has affected your ability to absorb the medication efficiently.

Finally, oral bioavailability indicates how much of an orally administered drug reaches the systemic circulation after being absorbed from the gastrointestinal tract into the blood or lymph vessels (this depends on many factors).

To understand bioavailability, you need to consider how the body processes drugs. The body has many ways of processing the drugs you take. It can metabolize them (the liver does this) or excrete them (the kidneys do this). Measuring bioavailability is about how much of the drug actually enters the bloodstream.

The extent of bioavailability is usually expressed by the variable AUC, which represents the area under the curve. In terms of how a drug is processed by the body, it's like seeing how much of that drug enters the bloodstream over time - so if you take a single dose and measure the effect over 24 hours, that would be a "dot" on the graph to which the AUC would apply.