bioavailabitly

Question 1

what is the definition of bioaviality

Answer 1

the chemical and physical properties of drug, formulation and administration rate influences the rate and extent of drug absorption

Question 2

what is the therapeutic window

Answer 2

this is the period of time where the drug is effective without causing significant side effects

Question 3

what happens if a drug has a large therapeutic window

Answer 3

the difference between the effective and the toxic threshold is very large, so it is able to experience variable absorption

Question 4

what happens if a drug has a smll therapeutic window

Answer 4

the difference bewteen the efffective and toxic threshold is small - meaning that the drug plasma levels need to be controlled

Question 5

what happens when a drug is absorbed orally

Answer 5

• the active ingredient of the drug is released
• the drug dissolution - this is when the drug is turnt into a solution.
• drug stability - this is the drugs ability to remain intact when exposed to different environments
• membrane penetration - the ability of teh drug to penetrate through the membrane
• first pass metabolism - this is when the drug goes through the kidney and how it is able to cope

Question 6

what factors affect the bioavailability

Answer 6

• disssolution rate
• permeation rate

Question 7

what is the flux

Answer 7

this is the number of particles that are moving past a given region divided by the area of that region

FICK’S FIRST LAW OF DIFFUSION

Question 8

how is dissolution rate calculated

Answer 8

dm/dt = DA(Cs-C)/h

dm/dt = rate of dissolution of the drug

D = diffusion co efficient

A = surface area

Cs = saturation solubility of drug in solution in diffusion layer

C = concerntration of drug in GI fluid

h = thickness of diffusion layer

Question 9

what are the types of diffusion across the membrane

Answer 9

• pararcwllular - the drug goes through the spaces in the membrane - this is dependant on the size of the particles
• trancelleular - this is when the particles go through the membrane - this is dependant on whether the particle is lipid soluble and how ionised

the different types of trans cellular
- passive diffusion
- endocytic diffusion
- carrier moderated transport

Question 10

what are the factors which affect drug absorption

Answer 10

• lipid solubility
• hydrogen bonding
• pH/pKa
• molecular size
• mechanisms of membrane transport

Question 11

what is the position co efficient

Answer 11

• this shows us the ability of teh drug to pass through the aqueous then the oil phase
• this can be found experimentally by shaking a substance in a mixture of ethanol and water

if the log P is bigger than 0 then it is more soluble in oil
log P is smaller than 0 then it is more soluble in water