8 - Kinetics - Elimination

Question 1

1) GFR is?
2) When can this be affected? If drops, what should you change about dosage of a drug?
3) Measure what specifically?

Answer 1

1) Glomerular Filtration Rate. Volume being pumped out per unit time.
2) Renal disease/kidney failure reduces clearance thus we need less dose since more dose will remain.
3) Creatine clearance. Expected to be constant. A waste product of muscles.

Question 2

1) Zero order elimination has metabolism that’s dependent on what?
2) First order elimination depends on…
3) Which one can easily overdose more on?

Answer 2

1) Enzyme saturation
2) Drug concentration.
3) Zero order since enzymes always saturated.

Question 3

1) Around how many half-lives does it take to get all the drug out?
2) Equation for calculation half-life?

Answer 3

1) 4 – 5
2) t1/2 = ln2/Ke (where Ke = CL/VD)
t1/2 = 0.693 x VD/CL

Question 4

1) First order elimination can be converted into a linear graph by…
2) In this new graph, a steeper slope indicates…

Answer 4

1) LogY axis (plasma conc.)
2) Higher elimination rate = lower half-life

Question 5

Describe how steady-state concentration changes over time assuming regular drug intervals (MDR)

Answer 5

After first dose, no drug is immediately available so %Css is zero. After 1st halflife, take 2nd dose. This 2nd dose isn’t immediately available either but the 1st dose’s drug is available at 50% (since 1 half-life has already taken place. After 3rd dose, 3rd dose isn’t available but 1st dose gives off 25% whilst 2nd dose gives off 50% for total = 75%. Continue pattern…