Simply put, Bioavailability is the term used for how much drug is lost or destroyed based on the route of administration. The book ends of this word Bioavailability would be and I.V. ( intravenous ) 100% Bioavailable Vs. Topical ( applying to skin ) 7% Bioavailable.
Clearly the higher the bioavailability of the delivery device or route of administration, the less drug you have to administer to achieve the same effect with a lower bioavailability.
Below are some basic examples of bioavailability.
Topical-trans dermal 7% to 10%
With the cost of Medication increasing day by day, why not use a device that get the most of it into you where it can be used effectively.