Editing Bioavailability (section)

== Relative bioavailability and bioequivalence ==

In pharmacology, relative bioavailability measures the bioavailability (estimated as the ''AUC'') of a formulation (A) of a certain drug when compared with another formulation (B) of the same drug, usually an established standard, or through administration via a different route. When the standard consists of intravenously administered drug, this is known as absolute bioavailability (see [[#Absolute bioavailability|above]]).

: <math>F_\mathrm{rel} = 100 \cdot \frac{AUC_\mathrm{A} \cdot D_\mathrm{B}}{AUC_\mathrm{B} \cdot D_\mathrm{A}}</math>

Relative bioavailability is one of the measures used to assess [[bioequivalence]] (''BE'') between two drug products. For FDA approval, a generic manufacturer must demonstrate that the 90% [[confidence interval]] for the ratio of the mean responses (usually of ''AUC'' and the maximum concentration, ''C''<sub>max</sub>) of its product to that of the "brand name drug"{{cref|OB}} is within the limits of 80% to 125%. Where ''AUC'' refers to the concentration of the drug in the blood over time ''t'' = 0 to ''t'' = ∞, ''C''<sub>max</sub> refers to the maximum concentration of the drug in the blood. When ''T''<sub>max</sub> is given, it refers to the time it takes for a drug to reach ''C''<sub>max</sub>.

While the mechanisms by which a formulation affects bioavailability and bioequivalence have been extensively studied in drugs, formulation factors that influence bioavailability and bioequivalence in nutritional supplements are largely unknown.<ref>{{cite journal |pmid=11285360 |year=2001 |last1=Hoag |first1=Stephen W. |last2=Hussain |first2=Ajaz S. |title=The Impact of Formulation on Bioavailability: Summary of Workshop Discussion |volume=131 |issue=4 Suppl |pages=1389–1391S |journal=The Journal of Nutrition |doi=10.1093/jn/131.4.1389S |doi-access= }}</ref> As a result, in nutritional sciences, relative bioavailability or bioequivalence is the most common measure of bioavailability, comparing the bioavailability of one formulation of the same dietary ingredient to another.