1 A patient weighing 60 kilograms is given a 1000 microgram

1. A patient weighing 60 kilograms is given a 1000 microgram dose of Drug A. On measuring the peak plasma concentration, Cp = 2 micrograms per liter.

a)Determine Vd.

b)The same patient is given 350 milligrams of Drug B, which distributes throughout extracellular fluid, but not readily into tissues. Cp = 20 milligrams per liter at its peak value. Determine Vd.

c) Compare the properties of Drug A and B.

Solution

1)

a) Vd (Volume od Distribution) = Ad / Cp divided by body weight

Ad = total amount of drug in the body

Cp = plasma concentration of drug

1000 microgram / 2 micrograms per liter = 500 liter

500 liter divided by 60kg = 8.33 liter per kilogram

b) 350 milligram / 20 milligram per liter = 17.5 liters of plasma

17.5 liter x 60 kg = 0.29 liter per kg

c) Compare the properties of Drug A and B :

volume distribution of two drug A and B due to different in lipid and water solubilities and plasma , tissue binding character.

Drug A has high solubility and Drug B has high water solubility indicates that they distributes into extracellular fulid only.