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Discussion Starter · #1 ·
A new aminoglycoside antibiotic is developed that is believed to be particularly effective against Pseudomonas. The volume of distribution of the drug is measured in a group of volunteers and is determined to be 4.5 L. This new drug is most likely to have which of the following properties?


It has low molecular weight
B. It is lipophilic
C. It does not bind to albumin
D. It is highly charged
E. It has high oral bioavailability


???? Just give me the answer, no need for any explanation.

Vd (L) = amount of drug given (mg) / plasma concentration of drug (mg/L)
 

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The volume of distribution (Vd) refers to a hypothetical volume of fluid into which the administered amount of drug would need to be uniformly distributed to produce the observed plasma concentration.

The volume of distribution is determined by administering a given amount of drug by the intravenous route and subsequently measuring the initial plasma concentration of the drug.

The average total body water is approximately 41 liters. Of that the extracellular fluid volume is about 14 L, or 1/3 of total body water. With in the extracellular fluid the plasma volume is about3 L, and interstitial fluid makes up the rest. Initially the drug enters the plasma compartment by the IV route.

If a drug has a large molecular weight, is bound extensively to plasma proteins or is highly charged (hydrophilic), then the drug generally remains in the plasma compartment and the volume of distribution is usually low as in the case above (about 3-5 liters).

If the drug has a small molecular weight but is hydrophilic, it can distribute into the interstitial fluid compartment outside of the blood vessels as well as in the intravascular compartment. In these cases the volume of distribution is limited to a total volume of about 14-16 liters (plasma volume plus interstitial volume).

If the drug has a small molecular weight and is also uncharged (hydrophobic or lipophilic), then the drug can cross cell membranes and reach intracellular compartment. These drugs have the highest volume of distribution (41 liters).

Drugs that are avidly bound in the tissues exhibit the highest volumes of distribution often much higher than the total body water volume, because these drugs accumulate readily within cells thereby maintaining low plasma concentrations.
 

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A new aminoglycoside antibiotic is developed that is believed to be particularly effective against Pseudomonas. The volume of distribution of the drug is measured in a group of volunteers and is determined to be 4.5 L. This new drug is most likely to have which of the following properties?

It has low molecular weight
B. It is lipophilic
C. It does not bind to albumin
D. It is highly charged
E. It has high oral bioavailability

the correct answer is D
 
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