If a drug is having Vd = 60L it indicates that drug is
Correct Answer: Sequestrated in tissue sites
Description: Ans) a (Sequestrated in tissue sites ) Ref Katzung 11th editionVolume of DistributionVd=total amount of drug in the bodyblood drug concentrationThe units for Volume of Distribution are typically reported in (ml or liter)/kg body weight.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.For example, these are volume of distribution of some of the drugs.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.The apparent volume of distribution reflects a balance between binding to tissues, which decreases plasma concentration and makes the apparent volume larger, and binding to plasma proteins, which increases plasma concentration and makes the apparent volume smaller.Changes in either tissue or plasma binding can change the apparent volume of distribution determined from plasma concentration measurements.Older people have a relative decrease in skeletal muscle mass and tend to have a smaller apparent volume of distribution of digoxin (which binds to muscle proteins). The volume of distribution may be overestimated in obese patients if based on body weight and the drug does not enter fatty tissues well, as is the case with digoxin.In contrast, theophylline has a volume of distribution similar to that of total body water. Adipose tissue has almost as much water in it as other tissues, so that the apparent total volume of distribution of theophylline is proportional to body weight even in obese patients.Abnormal accumulation of fluid- edema, ascites, pleural effusion- can markedly increase the volume of distribution of drugs such as gentamicin that are hydrophilic and have small volumes of distribution.
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Pharmacology
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