Drug-Drug interactions

Question 1

A drug interaction =

Answer 1

the modification of a drugs effect by prior or concomitant administration of another Drug, Herb, Foodstuff, Drink

Question 2

A drug interaction has occurred when

Answer 2

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

Question 3

types of drug interactions

Answer 3

• drug - drug interactions
• food - drug interactions
• herbal - drug interactions
• drink- drug interactions
• pharmacogenetic interactions

Question 4

Object drug =

Answer 4

The Drug whose Activity is effected by drug interactions

Question 5

Precipitant =

Answer 5

The agent which precipitates drug interaction

Question 6

Factors which modify drug action also include

Answer 6

• food
• smoking
• alcohol
• herbs

Question 7

Drugs Involved With Serious Interactions have

Answer 7

narrow therapeutic index.
examples include;
- Lithium
- Digoxin
- Warfarin
- Erythromicin
- Linezolid

Question 8

narrow therapeutic index means

Answer 8

that a small change in bood levels can induce profound toxicity.
- therapeutic drug monitoring is required

Question 9

Foods Interacting with Warfarin

Answer 9

vegetables

• Alfalfa
• Asparagus
• Broccoli
• Onions

Herbals

• Ginseng
• green tea

Miscellaneous

• avacado
• fish oils
• liver

Question 10

The probability of a drug-drug interaction increases exponentially with

Answer 10

the number of medicaments.

• the elderly
• the young
• the critically ill (patients who have chronic conditions)
• patients undergoing complicated surgical procedures

Question 11

drug - drug interactions may be severe in patients who have

Answer 11

• chronic conditions
• liver disease
• renal impairment
• diabetes mellitus
• epilepsy
• asthma

Question 12

Pharmacodynamic interactions include

Answer 12

• Antagonistic Interactions
• Additive or synergistic interactions
• Interactions due to changes in drug transport
• Interactions due to fluid and electrolyte disturbances
• Indirect pharmacodynamic interactions

Question 13

It is possible for one drug to alter the

Answer 13

• absorption
• distribution
• metabolism
• elimination
  of another drug

Question 14

we are able to predict

Answer 14

potential interactions but not who will have a clinically significant interaction

Question 15

Absorption interactions include

Answer 15

• Formation of insoluble complexes
• Altered PH.
• Altered bacterial flora..
• Altered GIT motility.

Question 16

most interactions of drugs in the GI tract change

Answer 16

absorption rate.

• Delayed absorption is important when a drug has a short half life or when we want high plasma levels rapidly
• Most interactions result in a delay in absorption and can be avoided if 2-4 hours are left between administration of the drugs

Question 17

Cholestyramine resin used to bind cholesterol in the

Answer 17

GI tract also binds to a variety of drugs e.g. warfarin, digoxin

Question 18

Absorption is affected by the degree of ionisation which is

Answer 18

dependent on pH.

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

Question 19

Bacterial flora are usually found in the

Answer 19

large bowel.

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

Question 20

Gastric emptying is the

Answer 20

rate limiting step.

• Many drugs which delay gastric emptying (anticholinergics, tricyclic anti-depressants, opiates)
• Some drugs increase gastric emptying and accelerate absorption of paracetamol, (domperidone, metoclopramide)

Question 21

After absorption drugs are distributed to the site of action

Protein-binding displacement occurs when

Answer 21

here is a reduction in the extent of plasma protein binding of a drug caused by the presence of another drug
- results in increased bioavailability of the displaced drug

Question 22

Drugs with Protein Binding >95%

Answer 22

Phenytoin
Valproic acid 
Warfarin
Diazepam 
Ibuprofen

Question 23

Drugs such as clarithromycin, erythromycin, cimetidine, ketoconazole, omeprazole, CCBs (diltiazem)

Answer 23

inhibit the cytochrome system.

Question 24

Metabolism commonly occurs in

Answer 24

the liver via the cytochrome P450 system

Question 25

potent inducers of cytochrome P450

Answer 25

Drugs such as barbiturates, carbamazepine, phenytoin, rifampacin and tobacco smoke

Question 26

Rifampicin increase

Answer 26

metabolism of Ciclosporin by inducing CYP 3A4

Question 27

St john’s wort increase

Answer 27

metabolism of ciclosporin by inducing CYP 3A4

Question 28

Most drugs are excreted in

Answer 28

Urine or Bile.

- Changes in GFR or tubular secretion

Question 29

Loop diuretics and lithium increase

Answer 29

tubular reabsorption

Question 30

Pharmacodynamic Interactions can be

Answer 30

direct
indirect
antagonistic
synergistic/agonistic

Question 31

Direct Antagonism include

Answer 31

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

Question 32

Synergistic Interactions is when

Answer 32

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

Question 33

Indirect Antagonistic Pharmacodynamic Interactions

Answer 33

• NSAIDs and antihypertensive medication

- NSAIDs and treatment for heart failure

Question 34

Pharmacodynamic Interactions Indirect Agonism

Answer 34

• Central Nervous System Depression
• Benzodiazepines and tricyclics or alcohol
• Warfarin and NSAIDs (Indomethacin)
• Atenolol and verapamil

Question 35

If the altering dose timing or no alternative doesn’t solve the issue

Answer 35

Adjust drug dosage ± monitor drug level (TDM) and physiological functions