W1 Clinical Pharm 6/2

Question 1

Bioavailability:

1. Definition
2. If oral bioavail is 50% of IV, how much drug will you have to give orally compared to IV?
3. What decreases oral bioavailability?

Answer 1

1. How much drug the body is exposed to.
2. 2X the amount
3. digaestion/ absorbtion and 1st pass metabolism (liver)

Question 2

2 Egs of drugs with low bioavailability

Answer 2

Morphine and GTN

Question 3

Volume of distribution=

Answer 3

Drug concentration in body= drug dose/ Vd

therefore Drug dose= drug concentration in body x volume of distribution

Question 4

Clearance=

Answer 4

volume of plasma cleared of drug/ time

= Vdx elimination constant (related to half life)

Question 5

What are the true liver function tests?

Answer 5

INR and albumin (LFTs measure liver injury)

Question 6

How many half lives does it take a drug to reach steady state/ be eliminated if it has 1st order kinetics?

Answer 6

4-5

Question 7

How do you double the steady state of a drug? How may half lives will this take?

Answer 7

If you double the dose (ie give twice as often or double dose at same frequency) it will take 4-5 half lives to reach double the steady state.

Question 8

Steady state of a drug?

Answer 8

Rate of absorption= rate of elimination

Question 9

How often should you dose someone to keep a certain drug in a steady state?

Answer 9

Every 1/2 life

Question 10

What is the main cause for drug-drug interactions?

Answer 10

Drugs are metabolised by the same CYP450 enzyme in the liver

Question 11

What is efficacy?

Answer 11

Intrinsic effect of a drug on a tissue

Question 12

What is potency?

Answer 12

The concentration of a drug required to achieve efficacy (eg highly potent drug: max effect will be at a low concentration)

Question 13

Zero order kinetics and implications therof:

Answer 13

Drug is eliminated per unit time rather than related to concentration:
Therefore if you double the dose you more than double the amount of drug in the body.

EG: phenytoin, aspirin in overdose.