Example: Procainamide is a class Ia antiarrhythmic drug that has an average CLT of 0.4 L/hr/kg. Calculate the renal clearance of procainamide if 60% of the administered iv dose is excreted unchanged in urine. What is the amount of procainamide excreted in urine after administration of 500 mg tablet that is known to have 80% bioavailability ?
Answer:
If 60% of the is procainamide dose is excreted in urine, its should be equal to 60% of the .
Amount excreted in urine:
The amount excreted in urine is 60% of the 400 mg bioavailable drug
Renal clearance = 0.6 X 0.4 L/hr/kg = 0.24 L/hr/kg
Bioavailable drug = 0.8 X 500 mg = 400 mg
Amount excreted in urine = 0.6 X 400 mg = 240 mg
