Lab 8: Effect Of pH On Drug Absorption

Question 0

What factors affect the rate of diffusion for a drug across a biological membrane?

Answer 0

Fick's law:
Concentration gradient
Area of membrane
Diffusion coefficient of drug
Thickness of membrane 

And the proportion of unionised drug present at the target site

Question 1

What is the henderson hasselbach equation?

Answer 1

PKa -pH = log [H-drug]/[drug]

Note that in weak acids, the drug is ionised, and in weak acids, the H-drug is ionised

Question 2

How is T60 evaluated?

Answer 2

This is the time taken for 60% or 3/5 fish to become sedated.

Question 3

How was quinaldine administered to goldfish?

Answer 3

Solutions were made using quinaldine stock and diluted with phosphate buffer.
Fish were transferred from a containing with tap water into the solution containing the drug.
when T60 was reached, or after 5 minutes, fish were removed from the drug solution and placed in a clean containing with fresh tap water

Question 4

What type of compounds are most drugs?

Answer 4

Organic compounds, i.e. Weak acids or weak bases which partially ionise in aqueous solutions.

Weak acids give up protons while weak bases accept protons

Question 5

Why is the law of mass applicable to weak acids and bases?

Answer 5

Because they exist in equilibrium between the ionised and unionised form.
Thus it is possible to change this equilibrium by changing the pH

Question 6

How do biological membranes behave?

Answer 6

As if they are simple lipid barriers to most drugs

Question 7

What is the main method of transport across membranes?

Answer 7

Passive diffusion, occurring down a concentration gradient according to the lipid molecule of the non ionised form of the drug,