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PoD > Drug-Drug interactions > Flashcards

Drug-Drug interactions Flashcards

1
Q

Definition of drug interaction

A

Modification of a drugs effect by prior or concomitant administration of another drug, herb, foodstuff, drink

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2
Q

What can interact with drugs?

A

Drugs, Herbs, food, drink and pharmacogenetic

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3
Q

What is the object drugs?

A

Drug whose activity is effected

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4
Q

What is the precipitant?

A

Agents which effects a drugs interaction

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5
Q

What factors modify drug action?

A

Smoking, food, alcohol and herbs

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6
Q

What can drug interaction treat?

A

Hypertension and Parkinsonism with carbidopa and levadopa

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7
Q

What is the risk of a patient seeing multiple doctors?

A

Dangerous as the different doctors prescribe different drugs

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8
Q

Name drugs involved with serious interactions

A
  • Lithium
  • Digoxin
  • Warfarin
  • Theophylline
  • Cylosporin
  • Macrolides
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9
Q

Importance of therapeutic drug monitoring

A

Drugs involved in serious reactions have a narrow therapeutic index - therefore small change in blood levels can induce toxicity

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10
Q

Name foods that interact with Warfarin

A

Vegetables: broccoli, brussellese sprouts, cabbage, onion, spinach

Herbals: green tea, tonic beans, woodruff

Miscellaneous: avocado, fish oils, liver, soybeans

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11
Q

Name the susceptible patents

A
  • Elderly
  • Young
  • Critically ill
  • Patients undergoing complicated surgical procedures
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12
Q

Conditions that can make patients more susceptible

A
  • Liver disease
  • Renal disease
  • Diabetes mellitus
  • Epilepsy
  • Asthma
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13
Q

Name the mechanisms of drug interactions

A
  • Pharmacodynamic

- Pharmacokinetic - ADME

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14
Q

What is ADME of drug pharmacokinetics

A 
One drug can alter a drugs:
Absorption
Distribution 
Metabolism 
Elimination
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15
Q

Describ pharmocodynamic drug interactions

A
  • Antagonistic or additive/synergistic
  • Due to to changes in drug transport
  • Due to fluid ad electrolyte disturbances
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16
Q

How can a drug alter ADME?

A

There is marked inter-individual variation in these process - so predict potential interaction but not able to predict who will have interaction

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17
Q

Possible absorption interaction outcomes

A
  • Formation of insoluble complexes
  • Altered pH
  • Altered bacterial flora
  • Altered GIT motility
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18
Q

Describe interaction of drugs in the GI tract and how can it be avoided?

A

Result in change of absorption rate rather than the extent of absorption - this is bad if drug has short half life when high plasma levels rapidly

Delayed absorption can be avoided if 2-4hrs are left between administration

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19
Q

What drugs bind in the GI tract?

A

Tetracycine and erythromycin complex with Fe, Ca, Mg

Cholestyramin resin binds cholesterol and also drugs (warfarin, digoxin)

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20
Q

How does changes in pH affect absorption?

A

Alters degree of ionisation - H2 antagonists, proton pump blockers and antacids reduce H+ and so increase the pH

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21
Q

What drugs alter pH?

A

H2 antagonist, proton pump blockers and antacids

They reduce H+ so increase pH

22
Q

Describe cause and effect of changes in GI bacterial flora

A

Broad spectrum antibiotics destroy normal gut flora and lead to failure of oral contraceptive or digoxin toxicity (nausea, vomiting)

23
Q

What is the rate limiting step in GI motility?

A

Gastric emptying

24
Q

What drugs delay gastric emptying?

A

Anticholinergics, tricyclic anti-depressants, opiates

25
Q

What drugs increase gastric emptying?

A

Domperidone and metoclopramide

26
Q

What is protein-binding displacement?

A

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

27
Q

What is the effect of protein-binding displacement?

A

Increases bioavailability of the displaced drug as only unbound drug is pharmacologically active

28
Q

Two important plasma proteins

A

Albumin and alpha1-glycoprotein

29
Q

Problem and solution of protein-binding displacement

A

1% displacement doubles the free plasma levels but patients are protected by increase in metabolism and excretion

30
Q

Examples of displacing drug

A

Indomethacin and warfarin

31
Q

How do drugs alter drug metabolism

A

One drug can induces or inhibits the metabolism of another - commonly occurs in the liver via the cytochrome P450 system

32
Q

What drugs inhibit the cytochrome P450 system in metabolism?

A

Macrolides, cimetidine, ketoconazole, omeprazole, CCBs (diltiazem)

33
Q

What drug inhibits metabolism of warfarin and diazepam by the cytochrome P450 system?

A

Cimetidine

34
Q

What drug inhibits metabolism of warfarin and alcohol by the cytochrome P450 system?

A

Metronidazole

35
Q

What drug inhibits metabolism of warfarin and phenytoin by the cytochrome P450 system?

A

Omeprazole

36
Q

What drugs induce cytochrome P450?

A

Barbiturates, carbamazepine, phenytoin, rifapacin and tobacco smoke

37
Q

What does enzyme induction (i.e. cytochrome P450) depend on?

A

Age, disease, genetic and concurrent drug therapies

38
Q

What drugs do phenytoin induce the metabolism of by cytochrome P450?

A

Warfarin, steroids and OC

39
Q

What drugs do rifampacin induce the metabolism of by cytochrome P450?

A

Warfarin, OC

40
Q

What drug does rifampacin increase the metabolism of by CYP 3A4?

A

Ciclosporin

41
Q

What drug does St John’s Wort increase the metabolism of by CYP 3A4?

A

Ciclosporin

42
Q

What are drugs excreted in?

A

Urine or bile

43
Q

How do drugs effect elimination/excretion?

A
  • Change GFR or tubular secretion

- Dogoxin and lithium are toxic agents eliminated by the kidney - problem could lead to their build up in blood

44
Q

What drugs inhibit excretion?

A

CCBs - verapamil, diltiazem

45
Q

What drugs increase tubular reabsorption in kidneys?

A

Loop diuretics and lithium

46
Q

When do pharmacodynamic interactions occur?

A

When 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

47
Q

What are the types of pharmacodynamic interaction?

A

Direct
Indirect
Antagonistic
Synergistic/Agonistic

48
Q

Describe direct antagonism of Pharmacodynamic interactions

A

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

49
Q

Describe synergistic interactions of pharmacodynamic interactions

A

When two drugs with the same pharmacological effect acting on the same receptor are given together

50
Q

Name drugs with indirect agonist effect and what the effect is

A
  • Warfarin (anti-coagulant) and NSAIDs (indomethacin) - bleeding becomes increased
  • Bendodiazepines (sedative) and tricyclics (anti-depressants) or alcohol - relax muscles and cause CNS depression
  • Atenolol and verapamil
51
Q

Drugs involved in indirect antagonistic interactions?

A

NSAIDS and antihypertensive medication or with treatment for heart failure

52
Q

How do you deal with an interaction?

A

If altering dose timing or an alternative drug does not solve the issue ADJUST drug dosage and monitor drug level (TDM) and physiological functions

PoD (35 decks)

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