PHA 5128
Fall 2004
HW 4
1. The disposition kinetics of a drug after IV bolus injection is described by a
one-compartment model. Assume the half life following therapeutic doses in
humans is 4hr, therefore:
a. What is its elimination rate constant?
b. How long does it take to eliminate 75% of the dose after injection of 5
mg.
c. How long does it take to eliminate 75% of the dose after injection of 1
mg.
2. A patient with liver failure was given 70mg of a drug as an IV bolus
injection. The plasma concentrations at 3 hours and 8 hours after injection
were 1.31mg/L and 0.65mg/L respectively. The drug is eliminated by
hepatic metabolism and renal excretion via glomerula filtration. The plasma
protein binding for the drug is 50%.. What is the hepatic clearance and the
volume of distribution of this drug in this patient? (Use 130ml/min for
glomerula filtration rate).
3. A 22 year old male patient (80kg, 66inches) was given 2mg/kg of an
aminoglycoside by IV bolus injection. The serum creatinine level of the
patient is 1.5mg/dL. Assume that the clearance of this drug equals the
creatinine clearance.
a. Calculate the creatinine clearance of this patient.
b. Blood samples were taken 1hour after the dose, and the plasma
concentration was 7.5mg/L. How long will it take for the plasma
level to reach 2mg/L?
