All of the following statements regarding bioavailability of a drug are true, EXCEPT:
The term bioavailability is used to indicate the propoion of unchanged drug that passes into the systematic circulation after oral administration, taking into account both absorption & local metabolic degradation. The systemic bioavailability of a drug can be predicted from the extent of absorption (function of concentration in plasma) and extraction ratio. So, low bioavailability does not neccessarily mean poor absorption. Ref: Essentials of Medical Pharmacology, 5th Edition, Page 15.
It is the fraction of unchanged drug that reaches the systemic circulation
Bioavailability of an orally administered drug can be calculated by comparing the Area Under Curve after oral and intravenous (iv) administration of the drug
Low oral bioavailability always and necessarily mean poor absorption
Bioavailability can be determined from plasma concentration or urinary excretion data.