Question

What is bioavailability and its importance? If a drug has 60% bioavailability,

Answer 1

Bioavailability

• The fraction absorbed into the systemic circulation is the drug's Bioavailabilty.

eg., If 100 mg of a drug are administered orally and 70 mg of this drug are absorbed unchanged, the bioavailability is 0.7 or seventy percent. Bioavailability: 3

• When a medication is administered intravenously, its bioavailability is 100%.

However, when a medication is administered via routes other than intravenous, its bioavailability is generally lower than that of intravenous due to intestinal endothelium absorption and first-pass metabolism. Thereby, mathematically, bioavailability equals the ratio of comparing the area under the plasma drug concentration curve versus time (AUC) for the extravascular formulation to the AUC for the intravascular formulation. AUC is utilized because AUC is proportional to the dose that has entered the systemic circulation.

Bioavailability is a measure of how easily a substance can be absorbed by the body. In pharmacology, for example, it refers to how quickly a drug enters the circulatory system and reaches the desired area, so that it can take effect. Nutritional scientists are well aware of the importance of bioavailability.

If the oral formulation of a drug has a bioavailability of 50%, one must double the drug dose to achieve the same concentrations in plasma as achieved using the intravenous formulation.

Irbesartan demonstrates a bioavailability in the 60%–80% range and does not exhibit a food effect. Losartan has a moderate bioavailability (≈33%) with 14% of an administered dose being transformed to the E-3174 metabolite. Telmisartan has a saturable first-pass effect with 42% and 58% bioavailability, respectively at doses of 40 and 80 mg. The estimated absolute bioavailability of azilsartan following administration of azilsartan medoxomil is approximately 60%. The intrasubject variability in ARB absorption is probably in the order of 25%–40%.