Drug Metabolism: Movement Through The Body

Question 1

What are the different routes of administration?

Answer 1

-intramuscular
-intravenous
-inhalation
-oral
-rectal
-percutaneous

Question 2

What is the goal in plasma concentration?

Answer 2

To achieve a therapeutic effect with no adverse effects

Question 3

What is absorption?

Answer 3

The process by which drug enters the bloodstream (consider method of administration and bioavailability)

Question 4

What is distribution?

Answer 4

The process by which drug reversibly leaves the blood stream and enters tissues/interstitial fluids

Question 5

What is metabolism?

Answer 5

The process by which the drug is transformed by the liver and other tissues

Question 6

What is excretion?

Answer 6

The process by which a drug is excreted in urine, faeces, or bile

Question 7

What are the 4 methods of movement into a cell?

Answer 7

-passive diffusion
-facilitated diffusion
-active transport
-endocytosis

Question 8

What is pKa?

Answer 8

The pH at which 50% of a substance is ionised

Question 9

Explain pH trapping of aspirin

Answer 9

Aspirin has a pKa of 3.5 so when it is in the stomach where the pH is very low, it will mostly be in its in-ionised state. This allows aspirin to pass through the phospholipid membrane as it is hydrophobic and go into the bloodstream where the pH is much higher. The high pH allows the aspirin to ionise and can no longer diffuse back through the membrane as it is negatively charged

Question 10

Where do weak bases and weak acids typically accumulate?

Answer 10

Weak bases typically accumulate in low pH whereas weak acids accumulate in high pH