Bioavailability

Bioavailability

• The fraction of an administered dose of unchanged drug that reaches the systemic circulation.

• Rate and extent to which the active ingredient or active moiety is absorbed from a drug product and becomes available at the site of action.

less than or equal to 1

• A number__________ that indicates the fraction of drug reaching the systemic circulation.

Bioavailability formula

Absolute Bioavailability

• Compares the bioavailability of the active drug in the systemic circulation following extravascular administration with the bioavailability of the same drug following intravenous administration

= close to 1 (0.99 / 100%) = efficient good

Absolute Bioavailability formuala

Relative Bioavailability

• The systemic exposure of a drug in a designated formulation (generally referred to as treatment A or reference formulation) is compared with that of the same drug administered in a reference formulation (generally referred to as treatment B or test formulation).

Relative Bioavailability formula

Frel >1 =

High systemic delivery cmprd to std

Frel <1 =

Low systemic delivery cmprd to std

• Physicochemical properties

• Gastric emptying rate

• Metabolism in intestinal wall

• Drug efflux from intestinal wall

• Hepatic first pass metabolism

Factors that Affect Bioavailability