L9 - Absorbtion 2 - Bioavailability & Micellar Substitution

Question 1

What are the routes that the following take for absorbtion:

aqueous solution

aqueous suspension

immediate release solid dosage form

Answer 1

Question 2

bioavailability

Answer 2

• the amount of drug that enter the systematic circulation and is accessible at the site of action

Question 3

what happens to poorly soluble drugs

what does this mean in terms of bioavailability

Answer 3

• poorly soluble drugs tend to be eliminated from the GIT before dissolution can occur
• therefore poor bioavailability

Question 4

what are the quantitative units that can be used to express solubility

Answer 4

g L^-1

g dm^-3

Question 5

WHat is complexation

give an example of how it occur

Answer 5

• Mucin which is present in the GI fluid form complexes with drugs and reduces absorbtion and biovailable

Question 6

how does adsorption occur

give an example

Answer 6

• the co-administration of drugs and medicine containing solid adsorbents (e.g. antidiarrheal mixtures) may result in the adsorbents intefering with absorbtion of drugs from the GI tract
• e.g. kaolin or charcoal can adsorb drugs and reduce their absorbtion

Question 7

adsorption

Answer 7

• adhesion of molecules of gas, liquid, or dissolved solids to a surface

Question 8

Chemical stability

wghat causes instability

Answer 8

• drugs that breakdown in the GI fluid will have reduced absorption and bioavailability
• instability can be caused by
  
  • stomach pH (acidic hydrolysis)
  • enzyme degradation

Question 9

give an example of an instable drug and how is this resolved

Answer 9

• omepraazole is activated in acidic environment
• decomposes before reaching target
• enteric coated tablet
  
  • acid protected
• other drugs that are unstable in gi fluid are often not administered orally

Question 10

surfacant molecule

Question 11

what is a surfactant molecule

Answer 11

• amphillic
  
  • contain both hydrophobic and hydrophillic groups

Question 12

what happens when a surfactant is added to water

Answer 12

• hydrophillic head sticks in water
• hydrophobic tail sticks out of the water
• found on the surface of water

Question 13

how are surfactants used in formulation

Answer 13

• designed specifcally for their surface-activity
• they are pharmacaologically inert excipients

Question 14

drug molecules with surfactant properties

Answer 14

• chemical structure designed for a particular pharmacological activity, may also infer some degree of surface-activity to the molecule
• adsorbs at interfaces
• not designed for surfactant properties

Question 15

what happens beyond the monolayer

Answer 15

Question 16

how are micelles formed

Answer 16

• when the interface is full the surfacatant must enter the bulk phase
• this results in the hydrophobic tails of the surfacatant being in contact with the aqueous phase
• at a certain concentration
  
  • the surfactant molecules aggregate into a structure whihc avoids the hydrophobic tail being in contact with the aq environment

Question 17

how are micelles and surfactants used

Answer 17

• washing
• non-polar tail interacts with grease
• polar head allows the grease to be washed off