Question

A 70 kg woman was administered 1000 mg of the drug as i.v. bolus. After its uniform distribution in the body, the plasma concentration of the drug was found to be 50 mg/L. What is its volume of distribution?

• A. 70L
• B. 500L
• C. 20L
• D. 0.1L

Answer 1

The Correct Option is C

To determine the volume of distribution (\(V_d\)) of a drug, we use the relationship between the dose administered, the plasma concentration, and the volume of distribution. The formula for calculating the volume of distribution is: 

\(V_d = \frac{Dose}{C_0}\)

Where:

• \(V_d\) is the volume of distribution (L)
• Dose is the amount of drug administered (mg)
• \(C_0\) is the plasma drug concentration at time zero (initial concentration) (mg/L)

In the given problem:

• Dose = 1000 mg
• \(C_0 = 50 \, \text{mg/L}\)

Substituting these values into the formula, we get:

\(V_d = \frac{1000}{50} = 20 \, \text{L}\)

Thus, the volume of distribution of the drug is 20 liters. This means that the initial drug concentration was evenly distributed in a volume of 20 liters in the body.

Conclusion: The correct answer is 20L.

This calculation helps in understanding how extensively a drug disperses into body tissues compared to the blood. A larger volume of distribution indicates more extensive distribution into tissues.