Question

A 70 kg subject received 10 mg of diazepam. The plasma concentration, extrapolated to time zero was 120 ng/ml. Calculate the (f)Vd in liters/kg.

Please make sure Vd is in L/kg!!

Answer 1

Solution.

The volume of distribution,V_d represents a hypothetical volume which relates the amount of drug in the body to the plasma concentration by the equation

where A_bis the amount of drug in the body which also equals the amount of administered drug, and C is the concentration of drug in the plasma.

As a 10 mg dose (or 10⁷ ng) is administered, and the plasma concentration, extrapolated to time zero is 120 ng/ml, the volume of distribution is

As the mass is 70 kg, it is 83.3/70 = 1.19 L/kg.