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Pharmacology - Principles > Drug Elimination - Lecture 5 > Flashcards

Drug Elimination - Lecture 5 Flashcards

1
Q

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

A

Minimum Effective Concentration (MEC)

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2
Q

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

A

Maximum Tolerated Concentration. (MTC)

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3
Q

What is the therapeutic window?

A

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

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4
Q

What defines how safe a drug is?

A

The larger the Therapeutic window the safer the drug

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5
Q

What is the Therapeutic Ratio calculated?

A

TR = MTC
——–
MEC

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6
Q

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

A

A high Therapeutic Ratio

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7
Q

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

A

A low Therapeutic Ratio

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8
Q

What is Pharmacokinetics?

A 
Pharmacokinetics is the mathematical analysis of all drug disposition factors 
Absorption
Distribution
Metabolism 
Excretion
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9
Q

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

A

Concentration(dose)/Volume of Distribution

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

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10
Q

What is Vd?

A

The volume of distribution

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11
Q

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

A

K abs

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12
Q

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

A

K el

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13
Q

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

A

It by-passes the absorption. (K abs)

It is place directly into Vd

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14
Q

What is first-order kinetics of a drug?

A

Rate of elimination is directly proportional to drug concentration

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15
Q

What is the half-life of a drug?

A

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

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16
Q

What is the half life dependent upon/related to?

A

It is inversely related to K el

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17
Q

How do you work out the half life?

A

Take the initial concentration(dose)

Take the concentration for when it has halved

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

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18
Q

What times are used to look for the half lives?

A

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

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19
Q

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

A

The initial plasma concentration is doubled

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

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20
Q

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

A

You prolong the effects of the drug by one half life

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21
Q

What is Clearance (Cl) ?

A

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

22
Q

What is the mathematical equation for the rate of elimination?

A

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

23
Q

What does the maintenance dose rate depend upon?

A

The Clearance

24
Q

What is the maintenance dose rate?

A

Dose per unit time required to maintain a given plasma concentration

25
Q

What are the units for the Clearance?

A

l/hr

Litres per hour

26
Q

What drives the rate of the elimination?

A

The Plasma concentration

27
Q

What does dosing to steady state mean?

A

rate of drug administration = rate of drug elimination

28
Q

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

A

Rate of elimination at steady state = ( Plasma Conc Steady State)

WHICH EQUALS

rate of administration must also = Cl x( Plasma Conc Steady State)

29
Q

How could the total clearance rate be calculated?

A

By the sum of all the clearance processes

30
Q

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

A

A syringe driver

31
Q

What is “Steady State” (Css) ?

A

The Concentration of drug in the body is constant

32
Q

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

A

It is reached after approximately 5 half-lives.

33
Q

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

A

The Infusion rate

34
Q

For Css how does oral administration differ?

A

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

35
Q

What is the Volume of Distribution? (Vd)

A

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

36
Q

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

A

Amount in Body = Vd X Plasma Conc

37
Q

What is the loading dose?

A

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

38
Q

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

A

The time for the concentration of drug in plasma to halve

39
Q

What two independent variable is t1/2 dependent upon?

A

Volume of distribution (Vd) and Clearance (Cl)

40
Q

What is meant by zero order elimination?

A

The elimination of drug at a constant rate (Straight line on graph)

(rather than at a rate that is proportional to their concentration )

41
Q

What are the units of the Volume of Distribution?

A

l/kg

42
Q

What is the loading dose?

A

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

43
Q

What is the purpose of living?

A

To die

44
Q

How can the loading dose be calculated for IV administration?

A

Loading Dose = Volume of Dist X Target Concentration

45
Q

How do you calculate the loading dose for oral administration?

A

Loading Dose = ( Vd x Target Conc ) / F

F is the amount of drug that reaches the systemic circulation

46
Q

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

A

It is proportional to Vd/Cl

47
Q

How can the half life be calculated?

A

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

48
Q

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

A

The drug is eliminated at a constant rate

49
Q

What is the other name for Zero Order Kinetics?

A

Saturation Kinetics

50
Q

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

A

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

51
Q

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

A

Phenotoin

Ethanol

Pharmacology - Principles (6 decks)

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