Pharmacokinetics

Question 1

What is pharmacokinetics?

Answer 1

quantitative description of drug disposition

Question 2

At therapeutic doses most elimination processes are 1st order, this means what?

Answer 2

rate of elimination is proportional to the amount of drug present; exponential decline curve if [drug] on y axis is linear scale and a linear decline if on log scale

Question 3

What is zero order elimination?

Answer 3

rate of elimination is constant, occurs when mechanism is saturated so a constant amount of drug is eliminated per unit time; linear decline on linear scale and concave decline on log scale described by constant Beta

Question 4

What is t=half life for a drug?

Answer 4

time necessary to eliminate 1/2 of the drug, independent of drug concentration, typically 4-5 half lives to eliminate >90%, if [drug] <10% it loses therapeutic effects; B or Kel is the rate elimination kinetic

Question 5

What is clearance? What factors affect it?

Answer 5

CL; volume of fluid from which drug is completely removed in a given period (mL/min or L/hr) or rate of elimination (hepatic metabolism + renal excretion) relative to [drug] in blood; CYP induction (increase CL, decrease t1/2), CYP inhibition (decrease CL, increase t1/2), and hepatic/renal failure (decrease CL, increase t1/2)

Question 6

what is volume of distribution? What factors effect it?

Answer 6

estimate of tissue distribution; aging (reduced muscle mass decreases Vd and t1/2) or obesity (increased adipose, increases Vd and t1/2)

Question 7

What is oral bioavailability? What is bioavailability of IV?

Answer 7

F; fraction of dose reaching systemic circulation; 100%

Question 8

What is the clinical significance of generic vs trademark?

Answer 8

FDA regulates bioavailability be between 80-125% of trade mark drug, must have similar bioequivalence,

Question 9

How long does it take for a drug to reach steady state?

Answer 9

4-5 half lives

Question 10

when would you want to use IV infusion? How do calculations change?

Answer 10

in hospital with short half life drugs or cant use oral; absence of peaks and troughs, F=1 for calculations

Question 11

what is a timed release tablet? why would you want this?

Answer 11

sustained release formulations for once-per day dosing, mechanism allowing for slower dissolution, allows less frequent dosing and increases patient compliance

Question 12

What are other routes for sustained release?

Answer 12

depot injections, transdermal patches or pumps