Elementary Pharmacokinectics

Question 1

What is the minimum effective concentration?

Answer 1

The amount of drug required to give an effect

Question 2

What is the maximum tolerated concentration?

Answer 2

The concentration where there is significant side effects

Question 3

What is the therapeutic ration?

Answer 3

the window between the MTC and MEC

TR=MTC/MEC

Question 4

What are “safe” drugs?

Answer 4

drugs with a high TR - penicillins and BZD

Question 5

What are unsafe drugs?

Answer 5

drugs with a low TR - cardiac glycosides, barbituates

Question 6

How is the initial concentration calculated?

Answer 6

Co=D/Vd

Question 7

What does the concentration depend on over time?

Answer 7

Kel - rate of elimination

Question 8

What sort of kinetics do most drugs follow?

Answer 8

first order

Question 9

What equation does drug fall according to?

Answer 9

Ct=Coe^-Kel.t

Question 10

What is the t1/2 calculated by?

Answer 10

t1/2 = 0.693/Kel

Question 11

What does increasing the dose do for drugs that exhibit first order kinetics?

Answer 11

increases Cp but does not affect Kel or t1/2

Question 12

What is clearance?

Answer 12

the volume of plasma cleared of drug in unit time

Question 13

What does clearance apply to?

Answer 13

drugs that exhibit first order kinetics

Question 14

What is the equation for rate of elimination?

Answer 14

Rate = Cp x Cl

Question 15

What does concentration drive?

Answer 15

elimination

Question 16

What is true at steady state?

Answer 16

rate of drug administration = rate of drug elimination

Question 17

What is the rate of elimination at steady state?

Answer 17

R=Cl x Cpss

Question 18

What is clearance the sum of?

Answer 18

all clearance processes i.e. renal, hepatic, other

Question 19

When is Css reached?

Answer 19

after 5 half lives regardless of route of administration

Question 20

What is the time to reach Css determined by?

Answer 20

t1/2 but not infusion rate

Question 21

How do you calculate Css in oral drugs?

Answer 21

Css = F*dose/Clp x dose interval

where F is oral bioavailability

Question 22

What is the volume of distribution?

Answer 22

the volume into which a drug appears to be distributed with a concentration equal to that of plamsa

Question 23

What is the equation relating to volume of distribution?

Answer 23

a proportionality constant relating the plasma concentration to the amount of drug in the body (Ab)
Ab=Vd xCp

Question 24

How would you determine Vd?

Answer 24

at time 0 - Ab = dose

then Cpo = dose/Vd so Vd = dose/Cpo on a graph with log Cp

Question 25

What is a loading dose?

Answer 25

an initial higher dose of drug given at the beginning of a course of treatment before stepping down to a lower maintenance dose

Question 26

What is the loading dose used for?

Answer 26

to decrease the time to steady state for drugs with a long half life?

Question 27

What is the equation for a loading dose using iv?

Answer 27

LD = Vd x Target Cp

Question 28

What is the equation for a loading dose using oral admin?

Answer 28

LD = Vd x Target Cp/F

Question 29

What does t1/2 give an index of?

Answer 29

the time course of drug accumulation
the time course of drug elimination
choice of dose interval

Question 30

What is the equation for t1/2?

Answer 30

t1/2 = 0.693 x Vd/Cl

Question 31

What are the independent variables when calculating t1/2?

Answer 31

Vd and Cl

Question 32

What is the elimination pattern in zero order kinetics?

Answer 32

initially eliminated at a constant rate and then convert to first order kinetic at a low concentration

Question 33

When can zero order kinetics occur?

Answer 33

when the plasma concentration of the drug is higher than the Km of the enzyme which metabolises it