Volume of distribution (Vd), represents the apparent volume into which the drug is distributed to provide the same concentration as it currently is in blood plasma. It is calculated by the amount of the drug in the body divided by the plasma concentration [19].
What does it mean if a drug has a high volume of distribution?
The larger the volume of distribution, the more likely that the drug is found in the tissues of the body. The smaller the volume of distribution, the more likely that the drug is confined to the circulatory system.
Why is volume of distribution important?
The volume of distribution is useful in estimating the dose required to achieve a given plasma concentration as A = C ·Vd, with A = amount of drug in the body ( ≈ dose, shortly after administration) and C = plasma concentration. Variation of Vd mainly affects the peak plasma concentration of the drug.
What is meant by volume of distribution?
Simply defined, the volume of distribution is the volume of plasma that would be necessary to account for the total amount of drug in the patient’s body, if that drug were present throughout the body at the same concentration as found in the plasma.
Does volume of distribution affect clearance?
Volume of distribution per se has no effect on clearance or on average steady-state blood levels.
What is drug distribution?
Drug distribution refers to the movement of a drug to and from the blood and various tissues of the body (for example, fat, muscle, and brain tissue) and the relative proportions of drug in the tissues.
What is the clinical significance of volume of distribution of drugs?
ABSTRACT: Volume of distribution is one of the most important pharmacokinetic properties of a drug candidate. It is a major determinant of half-life and dosing frequency of a drug. For a similar log P, a basic molecule will tend to exhibit higher volume of distribution than a neutral molecule.
What is the significance of the volume of distribution in compartment based analysis of drugs?
Two-compartment model. Volume of distribution (V) is an important indicator of the extent of drug distribution into body fluids and tis- sues. V relates the amount of drug in the body (X) to the measured concentration in the plasma (C).
What is a high Vd?
A drug with a high Vd has a propensity to leave the plasma and enter the extravascular compartments of the body, meaning that a higher dose of a drug is required to achieve a given plasma concentration. (High Vd -> More distribution to other tissue)
How is drug clearance calculated?
Another equation can calculate clearance. Clearance is equal to the rate at which a drug is removed from plasma(mg/min) divided by the concentration of that drug in the plasma (mg/mL).
What does the volume of a drug refer to quizlet?
It is the fluid volume that is required to contain the entire drug in the body at the same concentration measured. The volume of distribution has no physiologic or physical basis but is useful to compare the distribution of a drug with the volume of water compartments in the body.
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.
Is volume of distribution constant?
The volume of distribution is a proportionality constant, relating the total amount of drug present in the organism to its plasma concentration at the same moment.
Does volume of distribution affect half-life?
3.2.
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.
Which type of drugs have high volume of distribution?
In rough terms, drugs with a high lipid solubility (non-polar drugs), low rates of ionization, or low plasma protein binding capabilities have higher volumes of distribution than drugs which are more polar, more highly ionized or exhibit high plasma protein binding in the body’s environment.
What are the distribution compartments of a drug?
Drug distribution refers to the movement of a drug to and from the blood and various tissues of the body (for example, fat, muscle, and brain tissue) and the relative proportions of drug in the tissues.
Where are drugs distributed in the body?
After a drug enters the systemic circulation, it is distributed to the body’s tissues. Distribution is generally uneven because of differences in blood perfusion, tissue binding (eg, because of lipid content), regional pH, and permeability of cell membranes.
Why is drug distribution important?
Understanding drug distribution is important in establishing: The amount of drug available to the target organ to produce action. The amount of drug distribution to nontarget organs that could potentially result in an adverse drug reaction. The loading dose of drugs.
What is the volume of distribution of digoxin?
Digoxin is roughly 30 percent protein bound in the plasma and has a large volume of distribution (VD) of nearly 7 L/kg in healthy adults.
How do you calculate clearance from volume of distribution?
The clearance of substance x (Cx) can be calculated as Cx = Ax /Px, where Ax is the amount of x eliminated from the plasma, Px is the average plasma concentration, and Cx is expressed in units of volume per time.
What are high clearance drugs?
High extraction ratio.
These drugs are rapidly and extensively cleared from the blood by the liver (e.g. in a single pass). Their clearance depends primarily on hepatic blood flow, and binding to blood components is not an obstacle for extraction; the extraction is said to be non-restrictive or blood flow dependent.
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