What is bioavailability?

What Does bioavailability Mean

In order to know the meaning of the term bioavailability, it is necessary to start by knowing its etymological origin. In this case, we can establish that it is the result of the sum of two clearly differentiated parts:

-The noun “bios”, which can be translated as “life”.

-The word availability that has Latin origin and that is the result of the union of these components: the prefix “dis-”, which means “from top to bottom”; the verb “put”, which is synonymous with “put”; the particle “-ible”, which can be translated as “that can”; and the suffix “-dad”, which indicates “quality”.

Bioavailability , a term that the Royal Spanish Academy ( RAE ) does not include in its dictionary, is a term that refers to the speed and quantity with which a drug is absorbed and reaches its point of action in the body.

In other words, bioavailability refers to the time and fraction with which the active principle reaches its therapeutic target (the site of the body where it develops its action). This bioavailability is reflected in the measurement in the blood of the parameters of the drug in question, from the levels reached in the systemic circulation of the individual.
The highest concentration of the active substance in plasma or blood ; the time at which said concentration is recorded; and the area under the plasma concentration versus time curve are the main bioavailability parameters.
It can be stated that bioavailability refers to the percentage of the active principle found in plasma. The format of the drug (capsule, tablet, etc.), the route of administration (oral, intravenous, topical) and other factors cause the bioavailability to vary.
Bioavailability, in this way, can show that the efficacy of a drug changes according to how it is delivered. The same amount of an active ingredient works differently if it is administered as a capsule or if it is applied intravenously, to name one possibility. This is because, before reaching the blood circulation and the site of action , the drug has to overcome several organic barriers that cause losses in the original dose.
In this sense, we can establish that it is indicated that the injection of a drug has a bioavailability of 100% just after that. And it is that the active substance that it has has been administered directly through the blood.
Precisely for this reason, when it comes to a substance that is administered, for example, by oral route, the bioavailability is reduced. Yes, it will be below 100%. That's because once the drug enters the body through the mouth, it has to pass through the esophagus, stomach, and intestines.

In relation to the term that concerns us, we have to emphasize the existence of another that is used very frequently. We are referring to what is called bioequivalence. It is a term used to refer to the relationship that exists between two preparations of the same drug, with the same dosage and with a similar bioavailability.

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