Pharmacokinetics

Question 1

Factors affecting drug metabolism

Answer 1

1. Age: old - organs e.g. stomach pH, lower CO, slow GIT, increased fat:water
Young - immature liver, reduced fat:water
2. Gender - size and fat
3. Genes
4. Nutrition - albumin
5. Induction/inhibition enzymes
6. Drug/drug interactions
7. Disease - liver

Question 2

Define volume of distribution

Answer 2

Vd = D/C

Theoretical volume into which drug dissolves

Question 3

Define clearance

Answer 3

Cl = Ke x Vd

Ke = elimination rate constant 0.693/t1/2

Volume of blood cleared of drug per unit time

Question 4

Define bioavailability

Answer 4

F = AUCroute/AUCiv

The fraction of dose that reaches target tissue (i.e. systemic circulation)

Note: oral F = 1-ER (hepatic excretion ratio)

Question 5

Define steady state concentration and dosing rate

Answer 5

Css target range when elimination rate = admin rate

Dosing rate is how much drug is required to maintain Css
dR =Css x Cl

Question 6

Define loading and maintenance dose

Answer 6

Loading > maintenance, used to establish desired serum level

Dl = Css x Vd
Dm = dR x dosing int x t1/2
Dm = Css x Cl/F

Question 7

How many half lives to be considered cleared

Answer 7

4 t1/2’s = 94% eliminated