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All you need to know and more > 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
What cannot be predicted
Who will have a clinically significant interaction
26
What mechanisms can be used to disrupt absorption interactions
Formation of insoluble complexes Altered pH Altered bacterial flora Altered GIT motility
27
What do most type of DDI's involving absorption result in
Changes in absorption rate rather than the extent of absorption
28
When is delayed absorption important
When a drug has a short half life or when we want high plasma levels rapidly
29
What do most DDI's involving absorption cause and how can it be avoided
A delay in absorption | Avoided if 2-4 hours are left between administration of the drugs
30
Where do some drugs bind to each other
GI tract
31
Give examples of drugs which bind to each other in the GI tract
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
What is dependent on pH in regards to drug absorption
The degree of ionisation which will affect absorption
33
What can increase pH
H2 antagonists, proton pump blockers and antacids which reduce H+
34
What is bacterial flora normally found in the GI tract
Large bowel
35
What can destroy normal gut flora
Broad spectrum antibiotics
36
What can the destruction of normal gut flora cause
May lead to failure of oral contraceptive or digoxin toxicity
37
Where are most oral medicines abdorbed
Small intestine
38
What is the rate limiting step in drug absorption
Gastric emptying
39
Name some drugs which delay gastric emptying
Anticholinergics Tricyclic antidepressants Opiates
40
Name some drugs which increase gastric emptying and accelerate the absorption
Domperidone | Metoclopramide
41
What drug can stop gastric emptying
Codine
42
What happens after drugs are absorbed
They are distributed to the site of action
43
When does protein-protein displacement occur
When there is a reduction in the extent of plasma protein binding of a drug caused by the presence of another drug
44
What does the displacement of a drug from plasma protein result in
Increased bioavailability of the displaced drug
45
What form of drugs are pharmacologically active
Unbound
46
What can happen when 1% of 99% bound drug is displaced
Will lead to the doubling of free plasma levels
47
Which two proteins are important in distribution DDI's
Albumin | Alpha 1-glycoprotein
48
How are patients protected from the common distribution DDI's
By increased metabolism and excretion
49
Name some drugs which have over 95% protein binding
``` Clofibrate Diazepam Glyburide Ibuprofen Naproxen Oxazepam Thyroxine Warfarin ```
50
When do drug interactions involving metabolism occur
When one drug induces or inhibits the metabolism of another
51
Where does drug metabolism commonly occur
The liver via the cytochrome P450 system
52
Name some drugs that can inhibit the cytochrome system
``` Clarithromycin Erythromycin Cimetidine Ketoconazole Omeprazole CCBs ```
53
What in the cytochrome system do drugs inhibit
Inhibits the metabolism of a small group of drugs metabolised by the cytochrome P450 system
54
What can affect cimetidine
Warfarin | Diazepam
55
What can affect metronidazole
Warfarin | Alcohol
56
What can affect omeprazole
Phenytoin | Warfarin
57
Name some potent inducers of cytochrome P450
``` Barbiturates Carbamazepine Phenytoin Rifampacin Tobacco smoke ```
58
When can the effects of enzyme induction be seen
After 2-3 weeks
59
What are the effects of induction dependent on
Age Disease Genetics Concurrent drug therapy
60
What can rifampicin and St John's wort increase by inducing CYP3A4
Increase metabolism of ciclosporin
61
Where are most drugs excreted in
Urine | Bile
62
Name some toxic agents excreted by the kidney
Digoxin | Lithium
63
What can inhibit the excretion of verapamil/diltiazem and digoxin
CCBs
64
What do loop diuretics increase
Tubular reabsorption
65
What will effect drug excretion
Changes in GFR or tubular secretion
66
When do pharmacodynamic interactions occur
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
What type of pharmacodynamic interactions are there
Direct Indirect Antagonistic Synergistic/Agonistic
68
Give an example of direct antagonism
Beta-blockers such as atenolol will block the actions of agonists (e.g. bronchodilators such as salbutamol)
69
Give an example of synergistic interactions
When two drugs with the same pharma-cological effect acting on the same receptor are give concurrently
70
What effect can pharmacodynamic interactions have
May be additive or multiplicative
71
Give an example of indirect agonism and the drugs that can cause it
``` Central Nervous System Depression Caused by: Benzodiazepines and tricyclics or alcohol Warfarin and NSAIDs (Indomethacin) Atenolol and verapamil ```
72
Give examples of indirect antagonistic pharmacodynamic interactions
NSAIDs and antihypertensive medication | NSAIDs and treatment for heart failure

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