We start intravenous infusion of a drug using an infusion pump to ensure that the rate of drug delivery is constant . What one factor determines how long it will take for the drug to reach a steady-state concentration (CSS) in the blood? (LQ)
|A||Apparent volume of distribution|
a. Bioavailability is defined as the fraction or percentage of a drug that becomes available to the systemic circulation following administration by any route.
b. This takes into consideration that not all of an orally administered drug is absorbed and that a drug can be removed from the plasma and bio transformed by the liver during its initial passage through the portal circulation.
c. A bioavailability of 25% indicates that only 20 mg of the 80-mg dose (i.e., 80 mg x 0.25 = 20 mg) reached the systemic circulation.
d. Organ clearance can be determined by knowing the blood flow through the organ (φ) and the extraction ratio (ER) for the drug by the organ, according to the equation:
Clorgan = φ. ER
The extraction ratio is dependent on the amounts of drug entering the organ (arterial side; CA. and leaving it on the venous side (CV).