Absorption and administration

Question 1

What form does the drug have to be in in order to be absorbed by the GI tract?

Answer 1

Unionised, it is more lipophilic.

Question 2

What is the pH of stomach contents?

Answer 2

1.0-3.0

Question 3

What is the pH of the small intestine?

Answer 3

4.8-7.6

Question 4

What is the pH of the large intestine?

Answer 4

7.6-8.0

Question 5

What two factors does the extent of ionisation depend on?

Answer 5

1. The pH of the solution, the acid or the base it is dissolved in
2. On the strength of the weak acid or base

Question 6

What is the strength of the acid or base measured by?

Answer 6

pKa

Question 7

What does it mean if the pH and pKa values are the same?

Answer 7

Half the molecules will be ionised and half will be unionised.

Question 8

What form will many weak acids exist in the stomach?

Answer 8

Unionised

Question 9

What environment will weak acids be preferentially absorbed by?

Answer 9

Acidic

Question 10

Why is the main site for absorption the small intestine?

Answer 10

Largest SA
Thinnest membrane
Highest blood flow

Question 11

give the name for an ATP powered efflux pump

Answer 11

P-glycoprotein

Question 12

Where is P-glycoprotein found?

Answer 12

Apical surface epithelial cells of the small intestine

Question 13

What does P-glycoprotein do?

Answer 13

Pumps a wide range of drug substrates out of the cell and back into the gut lumen, reducing permeability.

Question 14

What sort of diffusion is absorption normally?

Answer 14

Transcellular passive diffusion

Question 15

How else can drugs be absorbed other than trancellular passive diffusion?

Answer 15

Carrier-mediated transport

Question 16

Give an example of a drug absorbed by carrier mediated transport and why it can be

Answer 16

L-DOPA (treating Parkinson’s disease), its an amino acid and the body has evolved to absorb them from the gut lumen.

Question 17

What is the transporter for penicillins and cephalosporins?

Answer 17

Oligopeptide transporter

Question 18

What is the transporter for privastatin (antihyperlipidaemic agent)?

Answer 18

Monocarboxylic acid transporters

Question 19

What is the transporter for Iron?

Answer 19

Divalent metal transporter and bound to haem by the haem carrier protein

Question 20

Where do drugs go once they have passed from the GI tract?

Answer 20

Enter the hepatic portal vein, to the liver and then to the inferior vena cava.

Question 21

What are the 3 major metabolic barriers for oral drugs?

Answer 21

1. Intestinal lumen (digestive enzymes)
2. Intestinal wall (intestinal first pass metabolism)
3. The liver (hepatic first pass metabolism)

Question 22

Why is it called the first pass effect?

Answer 22

It occurs on the first passage of the drug from the gut lumen into the body

Question 23

What is sublingual drug administration?

Answer 23

Drug is placed under the tongue and sucked.

Question 24

Why is absorption from sublingual drug administration rapid?

Answer 24

Good blood supply under the tongue, which drains into the jugular vein and then into the heart

Question 25

When is rectal drug administration useful?

Answer 25

When oral route is compromised.

Question 26

describe I.V. administration.

Answer 26

• 100% bioavailable
• Risks, requires supervised care and only used when necessary
• Useful in emergency situations due to immediate onset

Question 27

Where is the drug placed in I.M. and S.C. administration?

Answer 27

Connective tissue matrix

Question 28

What is the form of absorption into the blood and lymphatic vessels?

Answer 28

Paracellular passive diffusion

Question 29

Give 2 disadvantages of using I.M and S.C administration

Answer 29

1. Invasive, may require supervised care

2. Costly in comparison with oral drugs.

Question 30

What is lung parenchyma?

Answer 30

Term used to describe the functioning parts of the lung

Question 31

What does intranasal administration allow?

Answer 31

Direct absorption into the systematic circulation via the jugular vein, may enable drugs to cross the brain barrier

Question 32

What is tropical administration?

Answer 32

Local effects, drug is applied directly to the site.

Question 33

What is transdermal administration?

Answer 33

Patches-a depot of drug targeted for systematic absorption, must be lipid soluble.