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Q.	How to calculate volume distribution?	Related Search: Chemistry
	6ml of 0.04 M KmNO4 was added to 400ml water, this is part of intravenous infusion
A.	The volume of distribution is given by the following equation: Therefore the dose required to give a certain plasma concentration can be determined if the VD for that drug is known. The VD is not a physiologic value; it is more a reflection of how a drug will distribute throughout the body depending on several physicochemical properties, e.g. solubility, charge, size, etc. The units for Volume of Distribution are typically reported in (ml or liter)/kg body weight. The fact that VD is a ratio of a theoretical volume to a fixed unit of body weight explains why the VD for children is typically higher than that for adults, even though children are smaller and weigh less. As body composition changes with age, VD decreases. The VD may also be used to determine how readily a drug will displace into the body tissue compartments relative to the blood: Where: VP = plasma volume VT = apparent tissue volume fu = fraction unbound in plasma fuT = fraction unbound in tissue

Q.	Calculating volume of distribution of a drug?	Related Search: Medicine
	I am trying to work out the half life and volume of distribution of a drug, as part of exam revision. I have a table giving the conc. of drug in the plasma (ng per ml) at set times after dosing. We have been told that the drug was administered at 0.1mg per kg. Please help! BTW - the data was gained using rats. I'm actually studying a toxicology module in Chemistry, but felt this was the more appropriate place to put the question.
A.	drug for calculations for nurses by robert lapham and heather agar might help your revision

Q.	explain why it is easier to use an intravenous bolus dose of a drug to calculate the volume of distribution?	Related Search: Medicine
	please can some one help me with this question??
A.	Both answers right. You've got four main areas to take into account in pharmacokinetics: Absorption, Distribution, Metabolism and Excretion in that order. If you want to look at areas of distribution then you have to create an environment where Absorption factors are independant and won't have an effect. You can bypass worrying about how much drug will reach the systemic circulation and how much will be removed by popping the drug straight in, as quickly as possible.

Q.	Toxicology - Volume of distribution question?	Related Search: Medicine
	Simple Toxicology question that I can't make sense of. In rat: 50 mg/kg dose 10.87 mg/L plasma concentration Vd=dose/plasma concentration answer in L/kg Vd=50/10.87=4.6L/kg right? Except that that seems way too high. Especially since the compound (bisphenol) apparently doesn't accumulate in the tissues. What am I missing? Any help is greatly appreciated.
A.	This is good revision for me, so I had a go and got the same answer. So I googled it: [Link] :-)

Click on the word below to see the definition:

The volume of distribution (V_D) , also known as apparent volume of distribution, is a pharmacological term used to quantify the distribution of a medication between plasma and the rest of the body after oral or parenteral dosing. It is defined as the volume in which the amount of drug would need to be uniformly distributed to produce the observed blood concentration. ^[1]

Volume of distribution may be increased by renal failure (due to fluid retention) and liver failure (due to altered body fluid and plasma protein binding). Conversely it may be decreased in dehydration.

The initial volume of distribution describes blood concentrations prior to attaining the apparent volume of distribution and uses the same formula.

1 Equations
2 Examples
3 Sample values and equations
4 References
5 External links

[edit] Equations

The volume of distribution is given by the following equation:

${V_{D}} = \frac{\mathrm{total \ amount \ of \ drug \ in \ the \ body}}{\mathrm{drug \ blood \ concentration}}$

Therefore the dose required to give a certain plasma concentration can be determined if the V_D for that drug is known. The V_D is not a physiologic value; it is more a reflection of how a drug will distribute throughout the body depending on several physicochemical properties, e.g. solubility, charge, size, etc.

The units for Volume of Distribution are typically reported in (ml or liter)/kg body weight. The fact that V_D is a ratio of a theoretical volume to a fixed unit of body weight explains why the V_D for children is typically higher than that for adults, even though children are smaller and weigh less. As body composition changes with age, V_D decreases.

The V_D may also be used to determine how readily a drug will displace into the body tissue compartments relative to the blood:

${V_{D}} = {V_{P}} + {V_{T}} \left(\frac{fu}{fu_{t}}\right)$

Where:

V_P = plasma volume

V_T = apparent tissue volume

fu = fraction unbound in plasma

fu_T = fraction unbound in tissue

[edit] Examples

Further reading: Table of volume of distribution for drugs

Drug	V_D	Comments
Warfarin	8L	Reflects a high degree of plasma protein binding.
Theophylline, Ethanol	30L	Represents distribution in total body water.
Chloroquine	15000L	Shows highly lipophilic molecules which sequester into total body fat.
NXY-059	8L	Highly-charged hydrophilic molecule.

[edit] Sample values and equations

Variable	Abbreviation(s)	Example value	Formula
Dose (loading dose, or steady state/maintenance)	D (LD or MD)	1000 mg	=V_dC₀
Volume of distribution	V_d	25 L	=D/C₀
Concentration (initial or steady-state)	C₀ or C_ss	40.0 mg/L	=D/V_d
Biological half-life	T_½	14 h	=0.7/K_e
Elimination rate constant	K_e	0.05/h	=0.7/(T_½) =Cl/V_d
Elimination rate, or rate of infusion to balance elimination	K_in	50 mg/h	=C_ss×Cl
Clearance	Cl	1.25 L/h	=V_d×K_e
Bioavailability	F	1	$= \frac{[AUC]_{A}\times dose_{B}}{[AUC]_{B}\times dose_{A}}$

Note that the "0.7" constant is a commonly used log approximation, but not the actual value. Another commonly used approximation is 0.693 for -ln(0.5) = 0.69315...

[edit] References

^ "vetmed.vt.edu". http://cpharm.vetmed.vt.edu/VM8314/VM8314PharmaModeling.htm.

[edit] External links

v • d • e Medication > Pharmacology

Pharmacokinetics	ADME: Absorption • Distribution • Metabolism • Excretion (Clearance) Loading dose • Volume of distribution (Initial) • Rate of infusion Compartment • Bioequivalence • Bioavailability Onset of action • Biological half-life • Plasma protein binding Phase 1 reaction • Phase 2 reaction Therapeutic index (LD₅₀/ED₅₀)

Pharmacodynamics	Toxicity (Neurotoxicology) • Dose-response relationship (Efficacy, Potency) Antimicrobial pharmacodynamics: Minimum inhibitory concentration/Bacteriostatic • Minimum bactericidal concentration/Bactericide

Agonism and antagonism	Agonist: Inverse agonist • Irreversible agonist • Partial agonist • Superagonist • Physiological agonist Antagonist: Competitive antagonist • Irreversible antagonist • Physiological antagonist Other: Binding • Affinity • Binding selectivity • Functional selectivity

Other	Drug tolerance: Tachyphylaxis Drug resistance: Antibiotic resistance • Multiple drug resistance

Related fields/subfields	Pharmacogenetics • Pharmacogenomics • Neuropsychopharmacology (Neuropharmacology, Psychopharmacology)

Retrieved from "http://en.wikipedia.org/wiki/Volume_of_distribution"

Categories: Pharmacology | Pharmacokinetics

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