Pharmacokinetics in Practice L7

Question 1

Why do we need to be able to calculate kinetic parameters

Answer 1

To ensure that the dosage regimen results in the correct plasma concentration in all patients irrespective of disease state, capacity to eliminate, route of administration, age and other drug therapy

Question 2

define
1. bioavailability
2. volume of distribution
3. elimination half life
4. clearance

Answer 2

1. fraction of drug absorbed into bloodstream
2. space available to contain drug
3. rate of removal
4. efficacy of removal

Question 3

what is the one compartment model

Answer 3

absorption and elimination kinetics effect volume distribution
- simplified model that a human consists of a single well stirred compartment.
- Drug is absorbed, immediately distributed and subsequently eliminated.
- Rate it goes in and rate it goes out effects volume

Question 4

how does administering via IV affect plasma concentration
look at pp for graph

Answer 4

IV (infusion) admin of a dose (D) will increase plasma concentration from zero to steady state (Css)
- reaches Css after 4-5 half lives
- Concentration at Css depends on frequency of administration

Question 5

how does administering via oral affect plasma concentration
look at pp for graph

Answer 5

follows a lull then rise wave like pattern until steady state
- due to absorption

Question 6

what happens to curve on graph if dose is doubled or halved
look at pp for graph

Answer 6

If you double dose, get the same shaped curve but increased
if you half dose, curve inverses

Question 7

what is the rate it takes to reach steady state independent of

Answer 7

mode of administration

Question 8

what are kinetic orders

Answer 8

Relate the plasma concentration of a drug and its rate of elimination from the body

Question 9

describe the graph of first order kinetics and what it is

Answer 9

graph shows a curve
Decrease in drug is dependent on the plasma concentration
Concentration of the drug is the rate limiting factor
Exponential decrease
- most drugs fall into first order

Question 10

when plasma concentration is turned to log scale, graph shows a linear line
what is C0

Answer 10

concentration of drug when first administered
- worked out by extrapolating back to Y intercept
CO= D/Vd
D= concentration

Question 11

what is the two compartment model

Answer 11

Drugs will only enter the body tissues (peripheral compartment) via the plasma (central compartment).
- Predicts a fast and slow phase of distribution between the compartments.

Question 12

describe the graph of zero order kinetics and what it is

Answer 12

shows a straight linear line
Decrease in drug is independent of the plasma concentration
Rate is constant due to limiting factor
linear reduction
- Rate of fall does not vary with dose

Question 13

why is volume distribution important

Answer 13

It is used to calculate drug dose (loading)

Question 14

give the equation for volume distribution and drug dose

Answer 14

Vd= amount of drug in the body/ [drug] plasma

Question 15

what does plasma concentration effect

Answer 15

Plasma concentration of a drug dictates the ability of a drug to reach its target organ in an effective concentration, therefore defines dose

Question 16

if the Vd is high or low, what is the plasma concentration like

Answer 16

high: drug accumulates in peripheral tissues resulting in low plasma concentration
low: drug accumulates in plasma resulting in high plasma concentrations

Question 17

how is half life (t ½) calculated

Answer 17

T (1/2) = difference in time (t2 –t1)
pick a concentration- read time (T1)
pick half of that concentration- read time (T2)

Question 18

if drug administered IV or orally, what will curve looks like

Answer 18

IV: straight line
oral: slight curve- accounts for absorption