How Drugs Are Excreted

Question 1

Explain excretion via the lungs

Answer 1

Important route for excretion of volatile compounds is exhalation via the lungs
Extent of excretion is governed by alveolar concentration rather than solubility in blood
Greater conc difference, the greater the alveolar conc, greater the excretion

Question 2

Excretion via faces:
Enterohepatic circulation can have what effect on drugs excreted by this route?

Answer 2

Increase the half-life

Question 3

Examples of drugs excreted via faces

Answer 3

Amphetamine, methadone, phenytoin

Question 4

Why is neomycin used to treat bacterial infections in the gi tract?

Answer 4

Isn’t absorbed and won’t pass straight through the gi tract

Question 5

Net excretion =

Answer 5

Glomerular filtration - reabsorption + tubular secretion

Question 6

If 20mg of a drug is secreted into a nephron, 50 mg is reabsorbed and the net excreted is 130 mg, how much enters the nephron at the glomerulus?

Answer 6

Rearrange equation
Net excretion + reabsorption - tubular
130 + 50 - 20=160mg

Question 7

In glomerular filtration molecules <20kDa undergo?

Answer 7

Fitration under pressure

Question 8

An experimental drug is being developed, with one of the requirements being that it is easily excreted in the urine.

What property would have the biggest influence on this?

Answer 8

It undergoes significant phase 2 metabolism

phase II reactions, usually being a conjugation such as glucuronidation, serve to increase water solubility and hence facilitate excretion in the urine.

Question 9

clearance

Answer 9

volume of plasma cleared entirely of drug per unit time (ml/min)

Question 10

f plasma flow to the kidney is 600 ml/min & 50% of the drug is removed, then clearance is?

Answer 10

600 x 0.5=300ml/min