medical health pharmaceutical drugs

# What does volume of distribution tell us?

Last Updated: 9th June, 2020

23
The volume of distribution reflects the relationship between the amount of drug in the body at steady state and plasma drug concentration. The volume of distribution is a mathematical concept, which does not necessarily reflect a physiological or “real” distribution space.

Hereof, what is the significance of volume of distribution?

The volume of distribution (Vd) is a measurement of how a drug is dispersed in the body related to the measured plasma concentration. It's used to determine the loading dose of a drug, the half-life of a drug, medication clearance, and drug toxicity.

One may also ask, what does a low volume of distribution mean? Definition/Introduction Conversely, a drug with a low Vd has a propensity to remain in the plasma meaning a lower dose of a drug is required to achieve a given plasma concentration. (Low Vd -> Less distribution to other tissue)

In this regard, what does increased volume of distribution mean?

This means that most of the drug is in the tissue, and very little is in the plasma circulating. 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.

How does volume of distribution affect half life?

In brief : Half-life (t½) is the time required to reduce the concentration of a drug by half. The formula for half-life is (t½ = 0.693 × Vd /CL) renal failure with oedema) volume of distribution increases but clearance decreases, resulting in an unchanged half life (thus, it is a poor measure of drug clearance alone).

Professional

## 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. This is important when peak plasma concentration is essential for the therapeutic effect (e.g. hypnotics). Drug dosage must be adapted to the Vd for such drugs.

Professional

## What affects protein binding?

Within in vitro test systems, a range of test conditions, including source of protein, concentration of the tested antibiotic, temperature, pH, electrolytes, and supplements may influence the impact of protein binding.

Explainer

## What does protein binding mean?

Plasma protein binding refers to the degree to which medications attach to proteins within the blood. A drug's efficiency may be affected by the degree to which it binds. Common blood proteins that drugs bind to are human serum albumin, lipoprotein, glycoprotein, and α, β‚ and γ globulins.

Explainer

## What factors affect drug distribution?

Factors that influence distribution include blood perfusion, membrane permeability, plasma protein binding (PPB), regional pH gradients, and accumulation in fat and tissue reservoirs.

Explainer

## 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. After a drug is absorbed into the bloodstream (see Drug Absorption), it rapidly circulates through the body.

Pundit

## What is a redistribution Half Life?

Two half-lives can be described: the alpha half-life, the rate of decline in plasma concentrations due to the process of drug redistribution from the central to the peripheral compartment, and the beta half-life, the rate of decline due to the process of drug elimination due to metabolism.

Pundit

## What is half life of a drug?

The elimination half-life of a drug is a pharmacokinetic parameter that is defined as the time it takes for the concentration of the drug in the plasma or the total amount in the body to be reduced by 50%. In other words, after one half-life, the concentration of the drug in the body will be half of the starting dose.

Pundit

## How does protein binding affect volume of distribution?

A higher concentration in the sample leads to a lower apparent volume of distribution. Based on total drug concentration the apparent volume of distribution will be small when there is extensive binding to plasma proteins. About 99% of warfarin in plasma is bound to albumin leaving only 1% unbound.

Pundit

## What is steady state volume of distribution?

The volume of distribution at steady state, Vdss, is defined to be 'the volume of blood (plasma) apparently necessary, given the amount of compound in the body, to satisfy the observed blood (plasma) concentration'.

Pundit

## How does volume of distribution affect clearance?

Volume of distribution per se has no effect on clearance or on average steady-state blood levels. Although changes in tissue binding will affect partition coefficient and apparent volume of distribution, such changes will have no effect on average steady-state blood levels of either total or free drug.

Teacher

## How does obesity affect volume of distribution?

In obese compared with normal weight individuals, the total volume of distribution (Vd) is moderately increased (aminoglycosides, caffeine) or similar (H2-blockers, neuromuscular blockers), but the Vd corrected by kilogram of actual bodyweight is significantly smaller.

Teacher

## Why are prodrugs used?

Prodrugs can be used to improve drug delivery or pharmacokinetics, to decrease toxicity, or to target the drug to specific cells or tissues. Ester and phosphate hydrolysis are widely used in prodrug design because of their simplicity, but such approaches are relatively ineffective for targeting drugs to specific sites.

Teacher

## How is clearance related to the volume of distribution and K?

Clearance (Cl) and elimination-rate constant (kel): Clearance is defined as the volume of body fluid from which the drug is completely removed per unit time. The total body clearance is related to the volume of distribution of the drug and its elimination-rate constant.

Teacher

## How do you find peak concentration?

Time of Peak Concentration
By setting the rate of change of Cp versus time, dCp/dt, to zero and after some rearranging an equation for the time of peak can be derived. As an example we could calculate the peak plasma concentration given that F = 0.9, Dose = 600 mg, ka = 1.0 hr-1, kel = 0.15 hr-1, and V = 30 liter.

Reviewer

## What is peak plasma concentration of a drug?

Peak Plasma Concentration. Cmax is the highest inhibitor concentration reached in the blood in vivo and is an approximation of the inhibitor concentration (I) at the enzymes in the liver. From: Drug-Like Properties (Second Edition), 2016.

Reviewer

## What are the distribution compartments of a drug?

Distribution in pharmacology is a branch of pharmacokinetics which describes the reversible transfer of a drug from one location to another within the body. Once a drug enters into systemic circulation by absorption or direct administration, it must be distributed into interstitial and intracellular fluids.

Reviewer

## What is the significance of plasma level time curve?

In BE studies, the plasma concentration time curve is generally used to assess the rate and extent of absorption. AUC, the area under the concentration time curve, reflects the extent of exposure.

Reviewer

## What is steady state concentration?

Concentration at Steady-State. Steady-state concentration (Css) is defined as the time during which the concentration remains stable or consistent when the drug is given repeatedly or continuously (IV infusion).

Supporter

## What is VSS in pharmacokinetics?

Pharmacokinetics - Concepts and Applications. Contributor © Minh Vo. C- Steady-state volume of distribution (Vss) Steady state volume of distribution (Vss) reflects the actual blood and tissue volume into which a drug is distributed and the relative binding of drug to protein in these spaces.

Co-Authored By:

7

9th June, 2020

41