Bioavailability and Half-Life

Bioavailability: the rate at which a drug makes it to its destination and becomes available to the site of action for which it is intended

Describes the concentration of drug in systemic blood in relation to the amount of drug given
An IV injection (given directly into the bloodstream) has 100% of bioavailability because the drug does not have to be absorbed
Bioavailability of PO (by mouth) medication is rarely 100% and usually range from 10% to 50%

Half-Life: the amount of time it takes the body to break down and excrete one half of a drug

Time taken for the plasma concentration of the drug to decrease by 50%
Half-life is an important factor in the creation of drugs because it helps determine proper dosing intervals
Clearance is the amount of plasma from which a substance is removed per unit time

First Pass Effect: all drugs absorbed by the GI tract enter the portal blood supply, and go directly to the liver