Drug Interactions

Question 1

Define the Object Drug?

Answer 1

Risk of drug-drug interaction increases with number of drugs used

The drug whose activity is effected by interactions is the Object Drug

Question 2

Define the precipitant?

Answer 2

The agent which precipitates a drug interaction
Modifies object drugs ADME

Question 3

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

Answer 3

Parkinsonism is treated with levodopa & carbidopa.
Carbidopa prevents 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
Multiple different illness at same time
Genetic Polymorphisms

Question 6

List the drug specific risk factors:

Answer 6

Polypharmacy (use of multiple drugs)
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 (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
elderly/young
Critically Ill
Liver/renal impairment
Epileptic
Asthmatic
Diabetes Mellitus (diabetic)

Question 9

What are the characteristics of drugs involved in serious interactions?

Answer 9

Steep Dose-Response Curves
Narrow Therapeutic Index
Very high protein binding
Can Alter Renal Clearance
Induce/inhibit hepatic enzyme

Question 10

What are the 3 types of mechanisms for drug interactions?

Answer 10

Pharmacokinetic Interactions
Pharmaceutical
Pharmacodynamic

Question 11

What are pharmaceutical interactions?

Answer 11

Involving mixing two drugs in the same solution

Question 12

What is a pharmacodynamic interaction?

Answer 12

One drug alters another’s effect at its site of action

Question 13

What are the subtypes of pharmacodynamic interaction?

Answer 13

Additive/Synergistic or antagonistic
Direct or indirect

Question 14

Whats the difference between direct & indirect pharamcodynamic interactions?

Answer 14

Direct - one drug alters others effect directly by acting on the same receptor
Indirect - act on different receptors

Question 15

How do synergistic interactions occur?

Answer 15

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

Question 16

How do drug interactions affect absorption rates?

Answer 16

Form insoluble complexes (erythromicin & iron)
Alter pH causing another drug to ionise
Effect GUT motility
Alter bacterial flora

Question 17

How do drug interactions affect drug distribution?

Answer 17

One drug can displace a plasma protein-bound drug and change its bioavailability

Question 18

What normally protects patients from protein-binding displacement interactions?

Answer 18

Metabolism & excretion

Question 19

How do drug interactions affect metabolism rates?

Answer 19

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

Question 20

How do drug interactions affect elimination?

Answer 20

Some drugs affect Glomerular Filtration Rate or tubular secretion

Question 21

What do loop diuretics do?

Answer 21

Loop Diuretics increase tubular reabsorbtion