a- Absolute bioavailability:
It is the fraction of the administered dose that reaches the systemic circulation.
The absolute bioavailability is determined by comparing the amount of drug that reaches the systemic circulation after extravascular administration and after iv administration of the same dose of the same drug. This is because after iv administration the entire dose reaches the systemic circulation .
Compare oral and iv formulations
10 mg propranolol tablets
10 mg propranolol iv injection
The absolute bioavailability can have values between 0 when no drug is absorbed at all, to 1.0 when all the administered dose reaches the systemic circulation. The absolute bioavailability does not have units since it is a fraction, and can be expressed as percent absorbed ( 0% to 100%)
b- Relative bioavailability:
The bioavailability of a drug product relative to the bioavailability of a second drug product that contains the same active drug moiety.
The relative bioavailability is determined by comparing the amount of the drug that reaches the systemic circulation after administration of an oral drug product and an oral formulation of the same active drug moiety.
Compare different oral formulations
Solution
Capsule
Tablet
Drops
The relative bioavailability can have any positive value. It can be more than one because the dosage form under investigation may have higher bioavailability than the . The relative bioavailability is the ratio of the absolute bioavailability of different products for the same active drug.
