All of the following statements regarding bioavailability of a drug are true, EXCEPT:
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.