Week 6 Drug Therapeutic Monitoring

Question 1

One compartment model

Answer 1

The central compartment is blood, where the drug should rapidly reach equilibrium.
– assumes the concentration in blood = well-perfused sites.

Question 2

Curve: Drug concentration vs Time
equation

Answer 2

Exponential decay
c=c0*e^(-kt)

Question 3

half time =

Answer 3

0.693/k

Question 4

how to find elimination rate constant

Answer 4

k = magnitude of slope (ln(concentration) vs t)

Question 5

how many half lives for the drug to be completely eliminated from body

Answer 5

5 half lives

Question 6

what 2 routes mainly affect drug elimination

Answer 6

metabolism (gut/liver)
excretion (kidney/urine, bile, faeces)

Question 7

2 type of enzymes in drug metabolism

Answer 7

• oxidation by cytochrome p450 enzymes
• conjugation by UDP-transferases

Question 8

enzyme drug acetylation effect

Answer 8

acetylation inactivates drugs
fast acetylator is bad.

Question 9

CYP2D6 genetic mutation and drug suppression

Answer 9

tamoxifen -> endoxifen
the conversion requires the enzyme to have the active metabolite

Question 10

What factors affect excretion (renal)

Answer 10

1. filtration: kidney failure can have reduced excretion
2. secretion in proximal: drugs can compete for secretion
3. passive reabsorption

Question 11

complications of the elimination rate constant

Answer 11

it is the sum of elimination rates (metabolism, excretion…)
does not tell what elimination is occurring

Question 12

how to find volume of distribution

Answer 12

dose/concentration

Question 13

how to calculate clearance

Answer 13

volume * constant
Vd * elimination rate constant

Question 14

what is rate of clearance

Answer 14

clearance * concentration

Question 15

intravenous infusion (how long to steady state)

Answer 15

5 half lives

Question 16

what governs the concentration at steady state

Answer 16

infusion rate

Question 17

what governs how long to get to steady state

Answer 17

half life

Question 18

how to get loading dose (what is a loading dose)

Answer 18

to have an immediate effect before infusion:
dose = concentration * Volume

Question 19

how to find bioavailability (what is bioavailability)

Answer 19

some drugs are not injected intravenously. only a fraction of drugs taken orally will enter the blood.
Area under curve (non-intravascular oral dose/intravascular) = fraction

Question 20

how to calculate for rate of infusion to get to the desired concentration

Answer 20

rate of infusion = rate of clearance =
clearance * desired concentration