Drug Elimination - Lecture 5

Question 1

For a drug to be effective it must at least reach the?

Answer 1

Minimum Effective Concentration (MEC)

Question 2

For a drug to be safe and not cause unwanted effect it must be below the?

Answer 2

Maximum Tolerated Concentration. (MTC)

Question 3

What is the therapeutic window?

Answer 3

The different in concentration between the Maximum Tolerated Concentration and the Minimum Effective Concentration.

Question 4

What defines how safe a drug is?

Answer 4

The larger the Therapeutic window the safer the drug

Question 5

What is the Therapeutic Ratio calculated?

Answer 5

TR = MTC
——–
MEC

Question 6

In terms of Therapeutic Ratio, what will a safe drug have?

Answer 6

A high Therapeutic Ratio

Question 7

In terms of Therapeutic Ratio what will an unsafe drug have?

Answer 7

A low Therapeutic Ratio

Question 8

What is Pharmacokinetics?

Answer 8

Pharmacokinetics is the mathematical analysis of all drug disposition factors 
Absorption
Distribution
Metabolism 
Excretion

Question 9

What is the concentration of a drug equal to when it is dissolved in the body?

Answer 9

Concentration(dose)/Volume of Distribution

Cp (plasma conc) = Mass, amount in body(Ab)/Volume (Vd)

Question 10

What is Vd?

Answer 10

The volume of distribution

Question 11

What is the symbol for rate of absorption of a drug in Vd?

Answer 11

K abs

Question 12

What is the symbol for rate of elimination of a drug in Vd?

Answer 12

K el

Question 13

What happens if a drug is added rapidly by intravenous injection?

Answer 13

It by-passes the absorption. (K abs)

It is place directly into Vd

Question 14

What is first-order kinetics of a drug?

Answer 14

Rate of elimination is directly proportional to drug concentration

Question 15

What is the half-life of a drug?

Answer 15

The half life (t1/2) is the time take for Ct to fall by 50%

Question 16

What is the half life dependent upon/related to?

Answer 16

It is inversely related to K el

Question 17

How do you work out the half life?

Answer 17

Take the initial concentration(dose)

Take the concentration for when it has halved

This is the half life. (time time when it has halved)

Question 18

What times are used to look for the half lives?

Answer 18

The time when the concentration has changed from:
100 %–> 50%
50% –> 25 %

Question 19

What changes and what does not change when the initial dose of the drug is doubled?

Answer 19

The initial plasma concentration is doubled

The K el and the Half life (t1/2) does not change

Question 20

What are the effects if you double the initial concentration of the drug?

Answer 20

You prolong the effects of the drug by one half life

Question 21

What is Clearance (Cl) ?

Answer 21

The volume of plasma cleared of drug in a unit of time

Question 22

What is the mathematical equation for the rate of elimination?

Answer 22

K el = Clearance of a drug X Plasma concentration of the drug

Question 23

What does the maintenance dose rate depend upon?

Answer 23

The Clearance

Question 24

What is the maintenance dose rate?

Answer 24

Dose per unit time required to maintain a given plasma concentration

Question 25

What are the units for the Clearance?

Answer 25

l/hr | Litres per hour

Question 26

What drives the rate of the elimination?

Answer 26

The Plasma concentration

Question 27

What does dosing to steady state mean?

Answer 27

rate of drug administration = rate of drug elimination

Question 28

What can be said for the rate of elimination and rate of administration if a drug concentration is at steady state?

Answer 28

Rate of elimination at steady state = ( Plasma Conc Steady State) WHICH EQUALS rate of administration must also = Cl x( Plasma Conc Steady State)

Question 29

How could the total clearance rate be calculated?

Answer 29

By the sum of all the clearance processes

Question 30

What piece of equipment would be used to keep a drug at steady state?

Answer 30

A syringe driver

Question 31

What is "Steady State" (Css) ?

Answer 31

The Concentration of drug in the body is constant

Question 32

For a drug that exhibits first order kinetics, how long does it take to reach a steady state?

Answer 32

It is reached after approximately 5 half-lives.

Question 33

For drugs that exhibit first order kinetics, the steady state (ss) plasma concentration (Css) is linearly related to what?

Answer 33

The Infusion rate

Question 34

For Css how does oral administration differ?

Answer 34

Oral dosage not given constantly, therefore there are peaks and troughs of drug concentration. There is an average Css used

Question 35

What is the Volume of Distribution? (Vd)

Answer 35

The volume into which a drug appears to be distributed with a concentration equal to that of plasma

Question 36

How can the amount of drug in a body be calculated?

Answer 36

Amount in Body = Vd X Plasma Conc

Question 37

What is the loading dose?

Answer 37

A loading dose (LD) is an initial higher dose of a drug given at the beginning of a course of treatment before stepping down to a lower maintenance dose

Question 38

What is the half life of a drug? (t1/2)

Answer 38

The time for the concentration of drug in plasma to halve

Question 39

What two independent variable is t1/2 dependent upon?

Answer 39

Volume of distribution (Vd) and Clearance (Cl)

Question 40

What is meant by zero order elimination?

Answer 40

The elimination of drug at a constant rate (Straight line on graph) (rather than at a rate that is proportional to their concentration )

Question 41

What are the units of the Volume of Distribution?

Answer 41

l/kg

Question 42

What is the loading dose?

Answer 42

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

Question 43

What is the purpose of living?

Answer 43

To die

Question 44

How can the loading dose be calculated for IV administration?

Answer 44

Loading Dose = Volume of Dist X Target Concentration

Question 45

How do you calculate the loading dose for oral administration?

Answer 45

Loading Dose = ( Vd x Target Conc ) / F F is the amount of drug that reaches the systemic circulation

Question 46

What is the half life (t1/2)proportional to?

Answer 46

It is proportional to Vd/Cl

Question 47

How can the half life be calculated?

Answer 47

t1/2 = (ln2 x Vd) / (Clearance)

Question 48

What can the rate of elimination be said for a drug that is of Zero Order kinetics?

Answer 48

The drug is eliminated at a constant rate

Question 49

What is the other name for Zero Order Kinetics?

Answer 49

Saturation Kinetics

Question 50

For a drug of Zero Order Kinetics how does act at low concentrations?

Answer 50

It adheres to First Order Kinetics - The concentration is directly proportional to the elimination rate

Question 51

What are examples of drugs that adhere to zero order kinetics?

Answer 51

Phenotoin | Ethanol