Kidneys and drug excretion

Question 1

The Elimination of drugs from the body involves two process what are they?

Answer 1

Metabolism and excretion?

Question 2

What is Excretion?

Answer 2

Excretion is the removal of waste substances from body fluids, predominantly via urine formed in kidneys.

Question 3

Can you name other routes of elimination?

Answer 3

bile,
saliva,
sweat,
tears,
faeces,
milk
exhaled air.

Question 4

Are all drugs metabolised before excretion?

Answer 4

No, some drugs, such as aminoglycoside antibiotics are polar compounds and are excreted by the kidneys without being metabolised first.

Question 5

What three processes occur in the Nephron to aid in
secretion of drugs?

Answer 5

1. Glomerular filtration,
2. Tubular secretion and
3. Tubule reabsorption.

Answer 7

Drugs and/or their metabolised products are transported by the capillaries to the kidney tubule. Some drugs enter the tubule by glomerular filtration at the renal corpuscle. This acts like a sieve allowing small drugs and those not bound to plasma protein to filter from the blood into the Bowman’s capsule.
Large drugs like heparin or those bound to plasma-protein cannot be filtered and are poorly excreted by glomerular filtration.

Answer 8

The majority of drugs do not enter the kidney tubule by glomerular filtration but do so by tubule secretion. This is an active process since drugs are carried against a favourable chemical gradient from the capillary network into the tubule.
Tubule secretion involves two carrier systems – basic carriers which transport basic drugs (amiloride, dopamine, histamine), and acidic carriers for acidic drugs (frusemide, penicillin, indomethacin).
The process of tubule secretion can have a big impact on the speed that a drug is eliminated from the body. For example, penicillin readily enters the nephron by tubule secretion and is rapidly excreted from the body in the urine. In a situation where the therapeutic effect needs to be prolonged, agents can be administered that block tubule secretion to slow the excretion of the drug.

Question 10

How do the majority of drugs enter the kidney tubule?

Answer 10

Tubule secretion

Question 11

Penicillin is rapidly excreted?

Answer 11

True

Question 12

Reabsorption is Passive Diffusion?

Answer 12

True

Question 13

In alkaline urine, acidic drugs are more readily ionised?

Answer 13

True