Drug-Drug Interactions

Question 1

A drug interaction is defined by…

Answer 1

The modification of a drugs effect by PRIOR or CONCOMITANT (naturally occurring) administration of another drug, herb, foodstuff drink
OR
A drug interaction has occurred when the pharmalogical effect of two or more drugs given together is not just a direct function of their individual effects

Question 2

Types of things that can interact with drugs

Answer 2

Other drugs, Herbs, Food, Drink, Pharmacogenetic interactions, smoking, alcohol

Question 3

Object Drug

Answer 3

The drug whose activity is effected by an interaction

Question 4

Precipitant

Answer 4

The agent which precipitates such an interaction

Question 5

Parkinson’s treated with carbidopa and levadopa

Answer 5

Carbidopa - dopa decarboxylase inhibitor which prevents the systemic side effects of levadopa

Question 6

Warfarin

Answer 6

Blood thinner. (anticoagulant) Treats blood clots etc

Question 7

SSRI

Answer 7

Selective Serotonin Reuptake inhibitors (anti-depressants)

Question 8

Erythromycin

Answer 8

Treats various bacterial infections. eg chlamydia

Question 9

Therapeutic drug monitoring is important because

Answer 9

A small change in blood levels can induce profound toxicity

Question 10

SSRI, Lithium, Erythromycin etc

Answer 10

All are potent with a narrow therapeutic index

Question 11

Foods etc that interact with Warfarin

Answer 11

Broccoli, Asparagus, Kale, spinach. Green teas etc avocado, fish oils

Question 12

The more medications taken

Answer 12

the higher probability of drug-drug interactions

Question 13

Susceptible patients include chronic conditions such as

Answer 13

Liver disease, Renal Impairment, Diabetes, epilepsy, asthma

Question 14

Pharmacokinetics

Answer 14

Determining the bodies effect on the drug. Absorption, distribution, metabolism, elimination

Question 15

Pharmacodynamics

Answer 15

Determining the drugs effects on the body

Question 16

Pharmacokinetic interactions ADME

Answer 16

Absorption, distribution, metabolism, elimination of another drug

Question 17

Mechanisms of absorption interactions

Answer 17

Formation of insoluble complexes, altered pH, altered bacterial flora, altered GIT motility

Question 18

Absorption can be affected by ionisation which is dependent on…

Answer 18

pH

Question 19

Change in Bacterial Flora

Answer 19

Bacterial flora are usually found in the large bowel. Broad spectrum antibiotics destroy normal gut flora

Question 20

Rate limiting step of absorption

Answer 20

Gastric Emptying

Question 21

Most oral medicines are absorbed in the…

Answer 21

Small intestine

Question 22

Pharmacologically active drugs are…

Answer 22

unbound. The displacement of a drug (by another drug) from plasma protein results in increased bioavailability of the displaced drug.

Question 23

If a drug is 99% bound displacement of only 1% will lead to

Answer 23

a doubling of free plasma levels

Question 24

Drugs with protein binding >95%

Answer 24

Warfarin, Naproxen, Diazepam, Glyburide, Ibuprofen

Question 25

Drug metabolism

Answer 25

Drug interactions involving metabolism occur when one drug induces or inhibits the metabolism of another

Question 26

Metabolism occurs in the liver via the...

Answer 26

cytochrome p450 system

Question 27

Inducers of the P450 system

Answer 27

Barbiturates, carbamazepine, phenytoin and tobacco smoke Common example: Phenytonin --> Warfarin, steroids Rifampacin --> Warfarin

Question 28

Rifampicin increases metabolism of...

Answer 28

Ciclosporin (by inducing CYP3A4)

Question 29

St Johns Wort increases metabolism of

Answer 29

ciclosporin (by inducing CYP3A4)

Question 30

Digoxin and Lithium

Answer 30

Toxic agents that are eliminated by the kidneys

Question 31

Phamacodynamics interactions

Answer 31

Occur when the pharmacodynamics actions of a drug are changed due to the presence of another drug either acting directly on the same receptor or indirectly on different receptors AGONIST/ANTAGONIST (direct and indirect)

Question 32

Direct antagonism

Answer 32

Beta blockers (eg atenolol) will block the actions of agonists (eg salbutamol - bronchodilators)

Question 33

Synergistic interactions (agonists)

Answer 33

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

Question 34

Indirect agonism

Answer 34

CNS depression, nexodiazapines, Warfarin

Question 35

Indirect antagonism

Answer 35

NSAIDs and antihypertensive medication or NSAIDs and treatment for heart failure