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Membranes and Receptors > Sessin 9 - Pharmacokinetics > Flashcards

Sessin 9 - Pharmacokinetics Flashcards

0
Q

What is formulation of a drug?

A

Whether it is in tablet or liquid form

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1
Q

What three factors are considered in the pharmaceutical process?

A

Formulation, compliance and site of administration

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2
Q

How is compliance improved in the pharmaceutical process?

A

Produce a drug with simple regimens eg once daily (easier to remember)

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3
Q

What are the various sites of administration?

A

Inhalation, oral, sublingual, intravenous, intramuscular, subcutaneous, topical, transdermal partly and rectal

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4
Q

What are the advantages of having various routes of administration?

A

Enables the drug to be concentrated close to the site of action and reduces systemic absorption producing less side effects

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5
Q

Define bioavailability

A

The proportion of drug given (except iv) that reaches circulation unchanged

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6
Q

How is bioavailability measured?

A

Based on the amount and rate of availability

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7
Q

What determines the amount of drug available in circulation unchanged?

A

1st pass metabolism and gut absorption

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8
Q

How is bioavailability calculated?

A

Area under curve (oral)/area under curve (injected) x100

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9
Q

What is therapeutic ratio?

A

LD50/ED50 or maximum tolerated dose/minimum effected dose

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10
Q

What is the effective therapeutic window?

A

The range of drug concentration from the minimum effective dose to the maximum tolerated dose

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11
Q

Why is a small therapeutic window significant?

A

There is potential to cross into toxic levels when administering the effective dose

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12
Q

What is a maintenance dose?

A

The dose of drug which keeps the patient above the effective concentration but not reaching toxic levels

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13
Q

Why can slow releasing preparations of drugs be beneficial?

A

Slow releasing drugs allows the effective concentration to be reached and sustained over a long period of time without entering the toxic concentration

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14
Q

What is meant by first pass metabolism?

A

When drugs are administered orally, absorption into GI tract results in passage to the liver where it is metabolised and changed before it reaches the circulation.

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15
Q

Why is first pass metabolism problematic?

A

Only a small proportion of active drug reaches the circulation and thus target tissue unchanged.

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16
Q

How is first pass metabolism avoided?

A

Parenteral routes, rectal and sublingual routes

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17
Q

What are parenteral routes?

A

Not orally administered eg, iv, im, sc

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18
Q

When administered rectally, where do drugs drain into?

A

Both the portal and systemic systems

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19
Q

What is volume of distribution?

A

Theoretical volume into which the drug is distributed if this occurred instantaneously

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20
Q

What is meant by a low volume of distribution? What type of drug has this?

A

When the drug is distributed it is at low concentrations/volume
Hydrophilic as it dissolves in the plasma

21
Q

What is meant by high volume of distribution and what drug type has this?

A

There is a high concentration/volume as the drug does not dissolve
Hydrophobic which only dissolves in lipid

22
Q

Why is the concentration of therapeutically active drug lower than circulating conc of drug?

A

Only the drug which is biologically free is therapeutically active, the bound drug is not

23
Q

How does drug binding increase the half life of the drug?

A

Bound drug cannot be excreted

24
Q

What is an object drug?

A

The first drug to be administered during treatment

25
Q

Why are protein binding interactions important when the object drug is highly bound to albumin?

A

The drug will not reach the effective concentration by itself at a dose lower than albumin binding sites

26
Q

Why are protein binding interactions important when the object drug has a small volume of distribution?

A

The drug is widely available in the circulation and thus protein interactions must be taken into account in order to provide a high enough dose

27
Q

Why are protein binding interactions important when the object drug has a small therapeutic window?

A

The small therapeutic window means that if a precipitant drug is added, it may exceed the toxic threshold

28
Q

What is a class I drug and describe the dose in relation to albumin in the presence of a precipitant?

A

The object drug, given in doses lower than the number of albumin binding sites if being administered with precipitant drug

29
Q

What are class II drugs and describe the dose in relation to albumin?

A

The precipitant drugs used in doses greater than the number of albumin binding sites

30
Q

What is a precipitant drug?

A

A drug which displaces the object drug from albumin when administered

31
Q

With the addition of a precipitant drug, why does the steady state of an object drug restore in a few days?

A

As the free drug levels rise, elimination levels also rise

32
Q

Name some precipitant drugs of warfarin

A

Aspirin
Phenytoin
Sulfonamides

33
Q

Name some precipitant drugs of tolbutamide

A

Aspirin

Sulfonamides

34
Q

What is meant by first order kinetics?

A

Rate of elimination is proportional to drug level

35
Q

What is meant by zero order kinetics?

A

The rate of elimination reaches constant with the mechanism becoming saturated

36
Q

Is it possible to work out the half life of first order or second order drugs?

A

First order

37
Q

How many half lives does it take to achieve a new steady state?

A

5

38
Q

What is a loading dose and when is it used?

A

Administration of a dose of drug which will immediately reach the effective window instead of waiting for 5 half lives. This is used when the drug action is needed immediately

39
Q

What is the da get of using zero kinetic drugs?

A

The therapeutic response can suddenly escalate as elimination mechanisms saturate

40
Q

Give an example of zero kinetic drugs

A

Alcohol

Phenytoin

41
Q

In what two ways can drugs be eliminated?

A

Metabolism

Excretion

42
Q

Where does drug metabolism mainly occur?

A

Liver

43
Q

Briefly describe phase I and II of drug metabolism

A

Phase I - oxidation/reduction/hydrolysis to expose/add reactive group
Phase II - conjugation

44
Q

What is the main enzyme group used in drug metabolism?

A

Mixed function oxidises consisting of cyp p450 system

45
Q

Why are CYP enzymes particularly useful?

A

Low substrate specificity
Affinity for lipid soluble drugs
Inducible
Inhibitable

46
Q

Drugs can effect each other’s metabolism, when is it most likely to matter clinically?

A

When the drugs have a low therapeutic ratio (potential to become ineffective or toxic)
When the drug is being used at its minimum effective concentration(potential to make ineffective)
When drug metabolism follows zero order (potential to cause sudden increase in activity)

47
Q

Which fraction of drugs are filtered?

A

Free fraction

48
Q

During renal excretion, what is passive absorption dependant on?

A

Urine pH

49
Q

What effect does pH on weak acid absorption into tubule?

A

Acidic urine -> increased absorption as the acid remains un-ionised
Alkali urine-> acid is ionised -> decreased absorption

50
Q

How is aspirin poisoning treated?

A

Forced alkali diuresis

Membranes and Receptors (13 decks)

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