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Principles of Disease 16 > Drug-drug interactions > Flashcards

Flashcards in Drug-drug interactions Deck (23)
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1
Q

Discuss environmental factors which may predispose a patient to drug interactions

A

Food
Herbs
Drug intake
Alcohol intake

2
Q

Describe patients who may be more susceptible to DDIs

A

• Polypharmacy (~8 drugs 100% chance of DDI)
• The elderly
• The young
• The critically ill
• Patients undergoing complicated surgery
• Those patients who have chronic conditions e.g.
o Liver disease
o Renal impairment
o Diabetes mellitus
o Epilepsy
o Asthma

3
Q

What characteristics of a drug may make it more likely to cause a DDI?

A

Narrow therapeutic index
Potent or high dose
Known enzyme inducers or inhibitors
Protein or drug binding

4
Q

Name some vegetables that cause DDIs with warfarin

A
o	Alfalfa
o	 Asparagus
o	 Broccoli
o	 Brussel sprouts
o	 Cabbage
o	 Cauliflower
o	 Kale
o	 Lettuce
o	 Onions
o	 Spinach
o	 Turnip greens
o	 Watercress
5
Q

Name some herbs that cause DDIs with warfarin

A
o	Ginseng
o	 Green teas
o	 Melilot
o	 Tonka beans
o	 Woodruff
6
Q

Name some miscellaneous agents that cause DDIs with warfarin

A
o	Avocado
o	Fish oils
o	Liver
o	Soybeans
o	Papain
7
Q

Define drug-drug interations

A
  • A drug interaction is defined as the modification of a drugs effect by prior or concomitant administration of another Drug, Herb, Foodstuff, Drink
  • A drug interaction has occurred when the pharmacological effect of two or more drugs given together is not just a direct function of their individual effects
8
Q

What is the object drug in a DDI?

A

The drug whose activity is effected by such an interaction is called the “Object drug.”

9
Q

What is the precipitant in a DDI?

A

The agent which precipitates such an interaction is referred to as the “Precipitant”.

10
Q

Describe a useful DDI

A

o The treatment of Parkinsonism with carbidopa and levadopa

• Carbidopa is a dopa decarboxylase inhibitor and prevents the systemic side effects from levadopa

11
Q

Describe some pharmacodynamic mechanisms of DDIs

A

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

12
Q

Describe some absorption mechanisms that can cause DDIs

A

o Formation of insoluble complexes
o Altered PH.
o Altered bacterial flora e.g. OCP
o Altered GIT motility.

13
Q

How can you avoid absorption defects in DDIs?

A

Wait 2-4hr before next dose

14
Q

Name some drugs that are affected due to changes in bacterial flora

A

OCP

Digoxin

15
Q

Name some classes of drugs that can delay gastric emptying

A

anticholinergics
tricyclic anti-depressants
opiates

16
Q

Name some drugs that can increase gastric emptying

A

domperidone

metoclopramide

17
Q

Name the two most important plasma proteins involved in drug-protein binding

A

o Albumin

o α1-glycoprotein

18
Q

Name some drugs that inhibit cytochrome P450s

A
clarithromycin
erythromycin
cimetidine
ketoconazole
omeprazole
Calcium channel blockers (diltiazem)
19
Q

What drugs increase the metabolism of ciclosporin?

A

Rifampacin and St Johns wort

20
Q

Give an example of direct antagonism

A

Beta-1 selective beta-blockers such as atenolol will block the actions of agonists e.g. bronchodilators such as salbutamol

21
Q

Give an example of indirect antagonism

A

o NSAIDs and antihypertensive medication – both have different effects on BP, leads to uncontrollable BP and potentially RF
o NSAIDs and treatment for heart failure

22
Q

Describe some patient specific factors that increase the risk of DDIs

A
  • Advanced ages
  • Genetic polymorphisms
  • Concomitant diseases
  • Polypharmacy (~8 drugs almost 100% likelihood of DDI)
23
Q

Describe some drug specific factors that increase the risk of DDIs

A
  • Polypharmacy (~8 drugs 100% likelihood of DDI)
  • Narrow pharmaceutical range
  • Dose
  • Multiple prescribing physicians
  • Self prescription
  • Prolonged length of stay