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Flashcards in drug interactions Deck (26):
1

what is a drug interaction defined as?

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

2

when has a drug interaction occurred?

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

3

what are the drugs that are most commonly involved in drug interactions?

lithium
digoxin
warfarin
theophylline
cyclosporin
phenytoin
gentamicin

4

what increases the chance of a drug-drug interaction occurring?

higher number of medications
being very old or young
critically ill patients
patients undergoing complicated surgical procedures
patients with chronic conditions

5

what are the 3 mechanisms by which drug-drug interactions may occur?

pharmaceutical
pharmacokinetic
pharmacodynamic

6

what are some examples of pharmacodynamic interactions?

antagonistic interactions
additive or synergistic interactions
interactions due to changes in drug transport
interactions due to fluid and electrolyte disturbances
indirect pharmacodynamic interactions

7

what can happen in the GI tract with regards to absorption of drugs?

interactions can occur that change the rate of absorption rather than the extent ( mostly) clinically significant when drugs have short half lives or high plasma levels are required rapidly

8

what happens in the GI tract with regards to drug binding?

drugs can bind to each other (such as tetracyline and erythromycin complex with iron, calcium and magnesium)

9

why is pH significant in determining the absorption rate of a drug?

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

10

what can reduce pH?

H2 agonists, proton pump blockers and antacids

11

what is the effect of broad spectrum antibiotics on normal gut flora?

destroys normal gut flora - can lead to OCP failure or digoxin toxicity

12

where are most oral medicines absorbed?

small intestine

13

what is the rate limiting step of absorption of oral medicines?

gastric emptying

14

when does protein binding displacement occur?

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

15

what does displacement of a drug from plasma proteins result in/

increased bioavailability of the displaced drug

16

what are the two most important plasma proteins with regard to drug binding?

albumin
alpha 1 glycoprotein

17

when do drug interactions involving metabolism occur?

when one drug induces or inhibits the metabolism of another

18

where does metabolism occur?

commonly in the liver via the cytochrome p450 system

19

what drugs can inhibit the cytochrome system?

clarithromycin
erythromycin
omeprazole
CCBs
these drugs inhibit the metabolism of a small group of drugs metabolised by the cytochrome P450 system

20

what drugs can induce cytochrome P450?

barbiturates
phenytoin - warfarin, steroids
rifampicin - warfarin
tobacco

21

where does drug elimination occur?

the kidney

22

what can inhibit drug excretion?

vrapamil/diltiazem

23

what are the effects of loop diuretics?

increase tubular reabsorption

24

what can beta blockers interact with?

agonists such as salbutamol

25

what are synergistic interactions?

when two drugs with the same pharmacological effect are given concurrently

26

what do NSAIDs interact with?

antihypertensive medication and heart failure treatment