Drug - drug interactions Flashcards Preview

Principles of dizzees > Drug - drug interactions > Flashcards

Flashcards in Drug - drug interactions Deck (19):
1

What is a drug interaction?

Modification of a drugs effect by prior or concomitant administration of another drug, herb, foodstuff or drink

(Basically a drug reacting with something else that is in the body)

2

Drug X has effect Y
Drug Q has effect G

Drug X & Q interact with each other

Describe the clinical effect, in terms of the letters above

The effect of X & Q will not be a direct function of their individual effects

It WILL NOT BE: 'Effect Y + effect G'

3

What are the 5 types of drug interactions?

Drug - drug
Herbal - drug
Food - drug
Drink - drug
Pharmacogenetic

4

What is the difference between the object drug & the precipitant?

The 'object drug' is the one whose activity is affected by a drug interaction

The agent which causes (precipitates) such an interaction is the 'precipitant'

5

What are examples of drug interactions that are clinically beneficial/useful?

Treatment of hypertension

Treatment of Parkinsonism - carbidopa & levadopa

6

Drug interactions can affect the protein binding and bioavailability of a drug in a number of ways

Why might this lead to pathology?

Many drugs are potent with narrow therapeutic index (range)

Small changes in blood levels can induce serious toxicity

7

What are the 4 pharmacokinetic interactions?

ADME

Absorption
Distribution
Metabolism
Elimination

8

Through what mechanisms can drug interactions affect the absorption of another drug?

Altered pH

Formation of insoluble complexes

Altered bacterial flora

Altered GIT motility

9

How do drug interactions effect absorption, and how can this be avoided?

Generally will affect the rate of absorption, not the amount absorbed

Most can be avoided by leaving a couple of hours between administration of the 2 drugs or whaterr

10

What is protein-binding displacement?

*Distribution*

This occurs when there is a reduction in the extent of plasma protein (albumin + a1-glycoprotein) binding to a drug caused by the presence of another drug

The more unbound drug, the higher the levels of active (un-bound) drug in the blood stream

If a drug is normally 99% bound, a 1% increase in displacement means the levels in plasma double

11

What 2 drugs are commonly involved in protein-binding displacement?

Indomethacin & warfarin

12

How do drug interactions affect drug metabolism?

When the precipitant induces or inhibits the metabolism of a drug

13

What is a common way in which drugs can inhibit metabolism of other drugs?

(Drugs such as clarithromycin, erythromicin, cimetidine, ketocanazole, omeprazole, CCBs etc do this)

Inhibit the cytochrome P450 system in the Liver

This is where metabolism commonly occurs

14

What does Cimetidine inhibit the metabolism of?

Warfarin & diazepam

15

What does Metronidazole inhibit metabolism of?

Warfarin & alcohol

16

What does Omeprazole inhibit the metabolism of?

Phenytoin & warfarin

17

What does Phenytoin INDUCE the metabolism of?

Warfarin
Steroids
Oral contraceptives

18

What does Rifampacin INDUCE the metabolism of?

Warfarin & Oral contraceptives

19

What does St John's wort INDUCE the metabolism of?

Ciclosporin

By inducing CYP 3A4