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Principles of Disease > Drug Drug Interactions > Flashcards

Drug Drug Interactions Flashcards

1
Q

What is a drug interaction

A

The modification of a drugs effect by prior or concomitant administration of another Drug, Herb, Foodstuff, Drink

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2
Q

When does a drug interaction occur

A

When the pharmacological effect of two or more drugs given together is not just a direct function of their individual effects

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3
Q

What type of drug interactions can occur

A 
Drug - drug interactions
Herbal - drug interactions
Food - drug interactions
Drink - drug interactions
Pharmacogenetic interactions
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4
Q

What is an object drug

A

The drug whose activity is effected by such an Interaction

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5
Q

What is a precipitant

A

The agent which precipitates such an interaction

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6
Q

What factors can also modify drug action

A

Smoking

Alcohol

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7
Q

When are drug interactions not detrimental

A

The treatment of hypertension

The treatment of Parkinsonism with carbidopa and levadopa

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8
Q

What is carbidopa

A

A dopa decarboxylase inhibitor and prevents the systemic side effects from levadopa

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9
Q

How many patients are affected by detrimental interactions in hospitals

A

2.2-30%

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10
Q

How many patients are affected by detrimental interactions in GP’s

A

9.2-70%

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11
Q

Name some drugs involved with serious interactions

A 
Erythromicin
Clarithromicin
Warfarin
Gentamicin
SSRI
Lithium
Digoxin
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12
Q

What are some patient specific factors that can affect DDI’s

A

Advanced age
Genetic polymorphioms
Concomitant diseases

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13
Q

What are some drug specific factors that can affect DDI’s

A

Polypharmacy
Narrow therapeutic range
Dose

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14
Q

What are some other factors that can affect DDI’s

A

Multiple prescribing physcians

Self prescribing

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15
Q

What do drugs involved in serious interactions have in common

A

They are all potent with a narrow therapeutic index

So a small change in blood levels can induce profound toxicity

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16
Q

What can prevent drug toxicity

A

Therapeutic drug monitoring

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17
Q

What foods can interact with warfarin

A 
Asparagus
Broccoli
Brussel sprouts
Lettuce
Onions
Avocado
Fish oils
Green tea
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18
Q

What pateints are susceptible to DDI’s

A

Elderly
Young
Critically ill
Patients undergoing complicated surgical procedures

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19
Q

What increases the probability of DDI’s

A

Increases exponentially with the number of medicaments

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20
Q

What type of chronic conditions can make patients susceptible to DDI’s

A 
Liver disease
Renal impairment
Diabetes mellitus
Epilepsy
Asthma
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21
Q

What are the mechanisms of drug interactions

A

Pharmaceutical

Pharmacokinetic

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22
Q

What pharmacokinetic interactions can a drug alter

A

Absorption
Distribution
Metabolism
Elimination

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23
Q

What kind of pharmacodynamic interactions are there

A

Antagonistic Interactions
Additive or synergistic interactions
Interactions due to changes in drug transport
Interactions due to fluid and electrolyte disturbances
Indirect pharmacodynamic interactions

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24
Q

Why can potential interactions be predicted

A

As there is marked inter-individual variation in the ADME processes

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25
Q

What cannot be predicted

A

Who will have a clinically significant interaction

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26
Q

What mechanisms can be used to disrupt absorption interactions

A

Formation of insoluble complexes
Altered pH
Altered bacterial flora
Altered GIT motility

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27
Q

What do most type of DDI’s involving absorption result in

A

Changes in absorption rate rather than the extent of absorption

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28
Q

When is delayed absorption important

A

When a drug has a short half life or when we want high plasma levels rapidly

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29
Q

What do most DDI’s involving absorption cause and how can it be avoided

A

A delay in absorption

Avoided if 2-4 hours are left between administration of the drugs

30
Q

Where do some drugs bind to each other

A

GI tract

31
Q

Give examples of drugs which bind to each other in the GI tract

A

1) Tetracycline and erythromicin complex with iron, calcium, magnesium
2) Cholestyramine resin used to bind cholesterol in GI tract binds to a variety of drugs (e.g. warfarin, digoxin)

32
Q

What is dependent on pH in regards to drug absorption

A

The degree of ionisation which will affect absorption

33
Q

What can increase pH

A

H2 antagonists, proton pump blockers and antacids which reduce H+

34
Q

What is bacterial flora normally found in the GI tract

A

Large bowel

35
Q

What can destroy normal gut flora

A

Broad spectrum antibiotics

36
Q

What can the destruction of normal gut flora cause

A

May lead to failure of oral contraceptive or digoxin toxicity

37
Q

Where are most oral medicines abdorbed

A

Small intestine

38
Q

What is the rate limiting step in drug absorption

A

Gastric emptying

39
Q

Name some drugs which delay gastric emptying

A

Anticholinergics
Tricyclic antidepressants
Opiates

40
Q

Name some drugs which increase gastric emptying and accelerate the absorption

A

Domperidone

Metoclopramide

41
Q

What drug can stop gastric emptying

A

Codine

42
Q

What happens after drugs are absorbed

A

They are distributed to the site of action

43
Q

When does protein-protein displacement occur

A

When there is a reduction in the extent of plasma protein binding of a drug caused by the presence of another drug

44
Q

What does the displacement of a drug from plasma protein result in

A

Increased bioavailability of the displaced drug

45
Q

What form of drugs are pharmacologically active

A

Unbound

46
Q

What can happen when 1% of 99% bound drug is displaced

A

Will lead to the doubling of free plasma levels

47
Q

Which two proteins are important in distribution DDI’s

A

Albumin

Alpha 1-glycoprotein

48
Q

How are patients protected from the common distribution DDI’s

A

By increased metabolism and excretion

49
Q

Name some drugs which have over 95% protein binding

A 
Clofibrate 
Diazepam 
Glyburide 
Ibuprofen 
Naproxen
Oxazepam
Thyroxine
Warfarin
50
Q

When do drug interactions involving metabolism occur

A

When one drug induces or inhibits the metabolism of another

51
Q

Where does drug metabolism commonly occur

A

The liver via the cytochrome P450 system

52
Q

Name some drugs that can inhibit the cytochrome system

A 
Clarithromycin
Erythromycin
Cimetidine
Ketoconazole
Omeprazole
CCBs
53
Q

What in the cytochrome system do drugs inhibit

A

Inhibits the metabolism of a small group of drugs metabolised by the cytochrome P450 system

54
Q

What can affect cimetidine

A

Warfarin

Diazepam

55
Q

What can affect metronidazole

A

Warfarin

Alcohol

56
Q

What can affect omeprazole

A

Phenytoin

Warfarin

57
Q

Name some potent inducers of cytochrome P450

A 
Barbiturates
Carbamazepine
Phenytoin
Rifampacin
Tobacco smoke
58
Q

When can the effects of enzyme induction be seen

A

After 2-3 weeks

59
Q

What are the effects of induction dependent on

A

Age
Disease
Genetics
Concurrent drug therapy

60
Q

What can rifampicin and St John’s wort increase by inducing CYP3A4

A

Increase metabolism of ciclosporin

61
Q

Where are most drugs excreted in

A

Urine

Bile

62
Q

Name some toxic agents excreted by the kidney

A

Digoxin

Lithium

63
Q

What can inhibit the excretion of verapamil/diltiazem and digoxin

A

CCBs

64
Q

What do loop diuretics increase

A

Tubular reabsorption

65
Q

What will effect drug excretion

A

Changes in GFR or tubular secretion

66
Q

When do pharmacodynamic interactions occur

A

When the pharmacodynamic actions of a drug are changed due to presence of another drug either acting directly on the same receptor) or indirectly on different receptors

67
Q

What type of pharmacodynamic interactions are there

A

Direct
Indirect
Antagonistic
Synergistic/Agonistic

68
Q

Give an example of direct antagonism

A

Beta-blockers such as atenolol will block the actions of agonists (e.g. bronchodilators such as salbutamol)

69
Q

Give an example of synergistic interactions

A

When two drugs with the same pharma-cological effect acting on the same receptor are give concurrently

70
Q

What effect can pharmacodynamic interactions have

A

May be additive or multiplicative

71
Q

Give an example of indirect agonism and the drugs that can cause it

A 
Central Nervous System Depression
Caused by:
Benzodiazepines and tricyclics or alcohol
Warfarin and NSAIDs (Indomethacin)
Atenolol and verapamil
72
Q

Give examples of indirect antagonistic pharmacodynamic interactions

A

NSAIDs and antihypertensive medication

NSAIDs and treatment for heart failure

Principles of Disease (41 decks)

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