<prompt> What does the term bioavailability mean?Plasma protein binding degree of substancePermeability through the brain-blood barrierFraction of an uncharged drug reaching the systemic circulation following any route administrationAmount of a substance in urine relative to the initial doze  <response>: Bioavailability is defined as the fraction of unchanged drug reaching the systemic circulation following administration by any routeBasic and clinical pharmacology Katzung 13th edition pg 47 