PHA 5127

Excretion

1. Mark true or false. A renal clearance of 500 ml /min may suggest that:

the drug is eliminated only by glomerular filtration

the drug is eliminated by tubular secretion

drug interactions in renal tubules are likely

the drug is probably nonionized

the drug is extensively reabsorbed in renal tubules

2. Drug addicts sometimes abuse amphetamines in combination with sodium bicarbonate. What is the rationale of this emperically discovered interaction? What could be done to enhance the detoxification of an overdosed addict?

3. Which of the following factors does NOT influence glomerular filtration:

molecular size

protein binding

lipid solubility

number of functioning nephrons

renal blood flow

4. Select the correct answer(s). A renal clearance of 500 ml/min may suggest:

elimination by glomerular filtration

high protein binding

extensive metabolism

elimination by tubular secretion

reabsorption in renal tubules

5. Mark whether following statements are true or false

tubular secretion depends on the pH of urine

highly ionized substances tend to remain in the urine

tubular reabsorption can only be an active transport process

fluid is filtered across the glomerulus through passive diffusion

tubular secretion most often occurs with weak organic acids

6. A drug is eliminated almost exclusively by hepatic metabolism; renal and biliary excretion of unchanged drug account for less than 1 percent of total drug elimination. One route of metabolism is glucuronidation, with excretion of all of the glucuronide into the bile (flow rate is 50 ml/hr), at a concentration 110 times that of drug in blood. The excreted glucuronide is neither hydrolyzed in nor reabsorbed from the intestines. The volume of distribution VB (referenced to blood) and the half-life of this drug are 100 liters and 9 hours, respectively.

a) Is glucuronidation a major (more than 50 percent) route of elimination of the drug?

b) What is the hepatic extraction ratio of this drug? Hepatic blood flow is 1.5 liters/min.

c) Is the clearance of this drug more likely to be sensitive to a change in plasma protein binding or to a change in hepatic perfusion?

d) Will the half-life of this drug be changed in a patient with biliary obstruction? Briefly comment.

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