Drug to Drug interaction Flashcards Preview

0 > Drug to Drug interaction > Flashcards

Flashcards in Drug to Drug interaction Deck (36):
1

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

drug interaction

2

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

drug interaction

3

Factors which modify drug action -

drugs, food, smoking, alcohol, and herbs

4

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

with a narrow therapeutic index

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

5

Susceptible patients

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

6

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

precipitation
(pharmaceutical)

7

drug transport
fluid and electrolyte disturbance
indirect pharmacodynamics interactions

Pharmacodynamic interactions

8

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

clinically significant interaction

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

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

10

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

Object drug

11

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

Precipitant

12

Foods interacting with warfarin

veg, herbals, miscellaneous

13

absorption interactions

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

14

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

absorption rate
extent



15

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

tetracycline and erythromicin complex with iron, calcium, magnesium

16

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

warfarin, digoxin

17

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

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

18

Bacterial flora are usually found in

the large bowel


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

19

Most oral medicines are absorbed in the

small intestine

Gastric emptying in the rate limiting step

20

Drugs which delay gastric emptying

(anticholinergics, tricyclic anti-depressants, opiates

Absorption

21

Some drugs increase gastric emptying and accelerate absorption of paracetamol

Domperidone, Metoclopramide

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

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

23

Drugs with Protein Binding >95%

warfarin
Indomethacin

ketoconazole
Thyroxine
Diazepam
Ibuprofen


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?

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

Drug Metabolism

25

Potent inducers of cytochrome P450

,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

26

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

Rifampicin and St John's Wort
CYP 3A4

27

Most drugs are excreted in .... or .....

Urine
Bile

28

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

Digoxin and Lithium

29

...... inhibit ..... of
Verapamil/diltiazem and digoxin

CCBs
excretion

30

Loop diuretics increase .....

tubular reabsorption

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.

Pharmacodynamics interactions

32

Different types of pharmacodynamics interactions

Direct
Indirect
Antagonistic
Synergistic /Agonistic

33

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

Direct Antagonism

34

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

Synergistic Interactions


The effect may be additive or multiplicative

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

Pharmacodynamic Interactions Indirect Agonism

36

Monitor drug level

TDM