Ch10 CLINICAL PHARMACOKINETICS Flashcards
Clearance
Clearance is a measure of the body’s efficiency at removing a drug from the systemic circulation
Clearance is expressed as volume of plasma or whole blood cleared of drug (usually milliliters per minute
Elimination
is a measure of the time taken for clearance to occur
First-Order Drug Kinetics
the more drug that is in circulation, the more drug is cleared from circulation
The first-order kinetics exhibited during the clearance of a drug from the bloodstream means that the same volume of blood will be cleared per unit of time
regardless of drug concentration. It also means that the amount of drug cleared every moment fluctuates with drug concentration, so it can be hard to know the exact mass of drug that is eliminated.
Half-Life
the time it takes its drug concentration to decrease by half. Although the drug concentration in blood constantly changes during the process of drug clearance, there is a pattern to this change, and the half-life is constant
Only drugs that are eliminated by first-order kinetics have a half-life.
Zero-Order Drug Kinetics
the amount of drug cleared in every time period is the same and is not related to the total amount of drug in circulation. The physiological processes driving drug elimination in first-order and zero-order kinetics are the same. In the latter, however, there is too much drug for the clearance to be concentration dependent.
linear drug clearance over time.
no half-life!
Clearance Kinetics on Drug in Steady-State Concentration
If drugs are administered continuously (usually by intravenous infusion) instead of in discrete doses, an equilibrium or steady state normally forms between the amount of drug administered and the amount cleared by the body. This steady-state concentration (CSS) is to be expected because plasma clearance is a first-order process that will match infusion until the clearance is saturated
