Drug Interactions

Question 1

Define the Object Drug?

Answer 1

The drug whose activity is effected by an interaction

Question 2

Define the precipitant?

Answer 2

The agent which precipitates a drug interaction

Question 3

Give a case of a drug interactions that isn’t detrimental?

Answer 3

Parkinsonism is treated wiht levodopa & carbidopa.
The carbidopa prevents the systemic side effects of levodopa

Question 4

What are the 5 types of drug interaction?

Answer 4

• Drug
• Herbal
• Food
• Drink
• Pharmacogenetic

Question 5

List the patient specific risk factors for drug interaction:

Answer 5

• Old Age
• Concomitant Disease
• Genetic Polymorphisms

Question 6

List the drug specific risk factors:

Answer 6

• Polypharmacy
• Narrow Therapeutic Range
• HIgh Doses

Question 7

What other risk factors are there for drug interactions? [non drug or patient specific]

Answer 7

• Multiple Prescribing physicians
• Self-Prescription (both naughty doctors & over counter drugs)
• Prolonged stays in hospital

Question 8

Patients with what characteristics are most susceptible to severe (life threatening) drug interactions?

Answer 8

• many meds
• undergoing complex surgery
• are elderly
• are young
• Critically Ill
• Liver or renal impairment
• Epileptic
• Asthmatic
• Diabetes Mellitus (diabetic)
  AEDtic

Question 9

What are the characteristics of drugs involved in serious interactions?

Answer 9

• Steep Dose-Response Curves
• Narrow Therapeutic Indexs
• Very high protein binding
• Can Alter Renal Clearence
• Induce/inhibit hepatic enzyme

Question 10

Name some foods that can interact with drugs?

Answer 10

• Veg (Boccoli, spinach, cabbage)
• Herbals (ginseng, Green Tea)
• ‘Misc’ (avocado, fish oil)

Question 11

What are the 3 types of mechanisms for drug interactions?

Answer 11

Pharmacokinetic Interactions
Pharmaceutical
Pharmacodynamic

Question 12

What are pharmaceutical interactions?

Answer 12

Those involving mixing two drugs in the same solution

Question 13

What is a pharmacodynamic interaction?

Answer 13

Pharmacodynamic interactions are where one drug alters anothers effect at its site of action

Question 14

What are the subtypes of pharmacodynamic interaction?

Answer 14

Additive/Synergistic or antagonistic
Direct or indirect

Question 15

Whats the difference between direct & indirect pharamcodynamic interactions?

Answer 15

In direct interactions one drug alters the others effect directly by actin on hte same receptor.
In indirect interactions they act on different receptors.

Question 16

How do synergistic interactions occur?

Answer 16

2 drugs with the same pharmacological effect acting on the same receptor are given concurrently

Question 17

What are the 4 areas affected by pharmacokinetic drug interactions?

Answer 17

Absorption
Distribution
Metabolism
Elimination/Excretion

Question 18

How do drug interactions affect absorption rates?

Answer 18

• They can form insoluble complexes (erythromicin & iron)
• Alter pH causing another drug to ionise
• Drugs can effect GIT motility
• One drug can alter bacterial flora

Question 19

How do drug interactions affect drug distribution?

Answer 19

One drug can displace a plasma protein-bound drug possibly causing a massive change in its bioavailability

Question 20

What normally protects pateints from protin-binding displacement interactions?

Answer 20

Metabolism & excretion

Question 21

How do drug interactions affect metabolism rates?

Answer 21

• Inhibit the cytochrome P450 system in the liver
• Induces liver enzyme activity (takes weeks to build up)

Question 22

How do drug interactions affect elimination?

Answer 22

Some drugs affect Glomerular Filtration Rate or tubular secretion

Question 23

What do loop diuretics do?

Answer 23

Loop Diuretics increase tubular reabsorbtion