Drug to Drug interaction

Question 1

modification of a drugs effect by prior or concomitant administration of another drug

Answer 1

drug interaction

Question 2

……… has occurred when the pharmacological effect of two or more drugs given together is not just a direct function of their individual effects

Answer 2

drug interaction

Question 3

Factors which modify drug action -

Answer 3

drugs, food, smoking, alcohol, and herbs

Question 4

Those drugs most commonly involved with serious interactions and which give rise to serious toxicity are those ……

Answer 4

with a narrow therapeutic index

small change in blood levels = TOXIC!
require TDM
Lithium
Digoxin
OCP
Warfarin
Gentamicin
Cyclosporin
Fluconazole
Erythromycin
Clarithromycin
Ketoconazole

Question 5

Susceptible patients

Answer 5

elderly
young
critically ill
those going for complicated surgery
those with chronic condition (DM, asthma, epilepsy)

Question 6

The outcome of direct interaction between 2 drugs e.g. through IV

Answer 6

precipitation

pharmaceutical

Question 7

drug transport
fluid and electrolyte disturbance
indirect pharmacodynamics interactions

Answer 7

Pharmacodynamic interactions

Question 8

It is possible to predict potential interactions but possible to predict who will have a ……

Answer 8

clinically significant interaction

Question 9

Drug interactions affect absorption rate rather than the ….. of absorption. When the drug has short 1/2 life or when we want high [plasma], ….absorption is important

Answer 9

extent
delayed

Most interactions result in a delay in absorption and can be avoided if 2-4 hours are left between administration of the drugs

Question 10

The Drug whose Activity is effected by such an Interaction is called the..

Answer 10

Object drug

Question 11

The agent which precipitates such an interaction is referred to as the …

Answer 11

Precipitant

Question 12

Foods interacting with warfarin

Answer 12

veg, herbals, miscellaneous

Question 13

absorption interactions

Answer 13

formation of insoluble complexes
altered pH
altered bacterial flora
altered GIT motility

Question 14

The interaction of drugs result in changes in ……. rather than the ….. of absorption

Answer 14

absorption rate

extent

Question 15

Some drugs bind to each other in the GI tract, what are they?

Answer 15

tetracycline and erythromicin complex with iron, calcium, magnesium

Question 16

Cholestyramine resin used to bind cholesterol in the GI tract also binds to a variety of drugs e.g. ?

Answer 16

warfarin, digoxin

Question 17

Absorption is affected by the degree of ionisation which is dependent on pH

Answer 17

H2 antagonists, proton pump blockers and antacids reduce H+ and so increase the pH

Question 18

Bacterial flora are usually found in

Answer 18

the large bowel

Broad spectrum antibiotics destroy normal gut flora
May lead to failure of oral contraceptive or digoxin toxicity

Question 19

Most oral medicines are absorbed in the

Answer 19

small intestine

Gastric emptying in the rate limiting step

Question 20

Drugs which delay gastric emptying

Answer 20

(anticholinergics, tricyclic anti-depressants, opiates

Absorption

Question 21

Some drugs increase gastric emptying and accelerate absorption of paracetamol

Answer 21

Domperidone, Metoclopramide

Question 22

Protein-binding displacement occurs when there is a reduction in the extent of plasma protein binding of a drug caused by the presence of another drug

Answer 22

Distribution

The displacement of a drug from plasma protein results in increased bioavailability of the displaced drug

Another type: Protein-protein displacement

Only unbound drug = pharmacologically active

The two most important proteins are:
Albumin
1-glycoprotein
This type of interaction is common but patients are protected by increased metabolism and excretion

Question 23

Drugs with Protein Binding >95%

Answer 23

warfarin
Indomethacin

ketoconazole
Thyroxine
Diazepam
Ibuprofen

Question 24

Drug interactions involving metabolism occur when one drug induces or inhibits the metabolism of another.Metabolism commonly occurs in the liver via the cytochrome P450 system.

Which drugs inhibit the cytochrome system?

Answer 24

clarithromycin, erythromycin, cimetidine(inhibits warfarin,diazepam), ketoconazole, omeprazole(phenytoin, warfarin), CCBs
metronidazole (warfarin, alcohol)

Drug Metabolism

Question 25

Potent inducers of cytochrome P450

Answer 25

,phenytoin(warfarin, steroids, OC), rifampicin (warfarin, OC), tobacco smoke, barbiturates, carbamazepine

The effects of enzyme induction are not seen for 2-3 weeks
The effects of induction depend on age, disease, genetics and concurrent drug therapy

Question 26

….. increase metabolism of Ciclosporin by inducing…..

Answer 26

Rifampicin and St John’s Wort

CYP 3A4

Question 27

Most drugs are excreted in …. or …..

Answer 27

Urine

Bile

Question 28

……….. are toxic agents that are eliminated by the kidney

Answer 28

Digoxin and Lithium

Question 29

…… inhibit ….. of

Verapamil/diltiazem and digoxin

Answer 29

CCBs

excretion

Question 30

Loop diuretics increase …..

Answer 30

tubular reabsorption

Question 31

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.

Answer 31

Pharmacodynamics interactions

Question 32

Different types of pharmacodynamics interactions

Answer 32

Direct
Indirect
Antagonistic
Synergistic /Agonistic

Question 33

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

Answer 33

Direct Antagonism

Question 34

When two drugs with the same pharma-cological effect acting on the same receptor are give concurrently

Answer 34

Synergistic Interactions

The effect may be additive or multiplicative

Question 35

Central Nervous System Depression
Benzodiazepines and tricyclics or alcohol
Warfarin and NSAIDs (Indomethacin)
Atenolol and verapamil
NSAIDs (Increase BP) and antihypertensive (decrease BP) medication
NSAIDs and treatment for heart failure

Answer 35

Pharmacodynamic Interactions Indirect Agonism

Question 36

Monitor drug level

Answer 36

TDM