Is there a difference between half-life and terminal half-life?
SHALLOW part of curve —> ultimate excretion of drug, which is dependent on the release of the drug from tissue compartments into the blood. The longer half-life is called the terminal half-life and the half-life of the largest component is called the dominant half-life.
What is distribution half-life?
time curves. Half-life and Volume of Distribution. Half-life (t1/2) refers to the time required for plasma concentration of a drug to decrease by 50%. t1/2 is dependent on the rate constant (k), which is related to Vd & clearance (CL).
How does distribution affect half-life?
Half-life is dependent on both clearance and volume of distribution, such that a decrease in clearance, as might be seen with a CYP1A2 or CYP2C19 substrate, or an increase in volume of distribution will prolong the half-life and lead to a longer dosage interval.
What does terminal half-life of a drug mean?
Terminal half-life is the time required for the plasma concentration to fall by 50% during the terminal phase, and not the time required to eliminate half the administered dose.
Is EC50 same as half-life?
For concentrations in the range of the EC50 value with the Hill coefficient (H = 1), the pharmacodynamic half-life will be 1.6-2.0 times the kinetic half-life (T1/2dyn < or = 2.0 T1/2kin).
What is the difference between duration of action and half-life?
The duration of action of a drug is known as its half life. This is the period of time required for the concentration or amount of drug in the body to be reduced by one-half. We usually consider the half life of a drug in relation to the amount of the drug in plasma.
What is drug distribution?
Drug distribution is the disbursement of an unmetabolized drug as it moves through the body’s blood and tissues. The efficacy or toxicity of a drug depends on the distribution in specific tissues and in part explains the lack of correlation between plasma levels and the effects that are seen.
How does volume of distribution affect drug therapy?
Vd can be used to determine the size of a loading dose in order to quickly reach the required therapeutic plasma concentration, assuming that successful therapy is directly linked to the plasma concentration and that there are no adverse effects if a quite large dose is rapidly administered.
Why does the volume of distribution affect the half-life of a drug?
Elimination half-life is increased by an increase in volume of distribution or a decrease in clearance, and vice versa. This is because a decrease in the efficiency of elimination (and therefore in clearance) would, of course, cause an increase in the time needed to reduce the plasma concentration by 50 percent.
How many half-lives before a drug is cleared?
Even further, 94 to 97% of a drug will have been eliminated after 4 to 5 half-lives. Thus, it follows that after 4 to 5 half-lives, the plasma concentrations of a given drug will be below a clinically relevant concentration and thus will be considered eliminated.
What is the difference between EC50 and IC50?
The EC50 is the concentration of a drug that gives half-maximal response. The IC50 is the concentration of an inhibitor where the response (or binding) is reduced by half.
What is Emax and EC50?
E is the effect at drug concentration C, Emax is the maximal effect at high drug concentrations when all the receptors are occupied by the drug, and EC50 is the drug concentration to give the half-maximal effect.
What does distribution mean in pharmacokinetics?
Distribution is the process by which drug passes from the bloodstream to body tissues and organs. It is how a drug moves from intravascular space, e.g. blood vessels, to extravascular space, e.g. body tissues, as it is carried around the body by the circulatory system (figure 1).
What is distribution and redistribution of a drug?
Redistribution refers to the change in the plasma drug concentration which is significant enough to cause alteration/termination of drug action. The alteration of plasma concentration occurs due to the second phase of drug distribution. The commonest example is the redistribution of thiopentone.
How does volume of distribution affect duration of action?
Curve D has a smaller volume of distribution due to a lower degree of lipophilicity. This leads to a higher peak plasma concentration and a more prolonged distribution phase, causing an increase in the duration of action.
What does volume of distribution tell you?
The VD of a drug represents the degree to which a drug is distributed in body tissue rather than the plasma. VD is directly proportional with the amount of drug distributed into tissue; a higher VD indicates a greater amount of tissue distribution.