Drug-Drug Interactions Flashcards Preview

Principles of Disease > Drug-Drug Interactions > Flashcards

Flashcards in Drug-Drug Interactions Deck (38):
1

Drug interaction

the modification of a drugs effect by prior or concomitant administration of another drug, herb, foodstuff or drink.

2

What type of drug interactions are there?

-food
-drink
-pharmacogenetic
-herbal
-drug

3

Object drug

the drug whose activity is effected by and interaction

4

Precipitant

the agent which precipitates such an interaction

5

What do drugs involved in serious interactions have in common?

-they are all potent with a narrow therapeutic index
-this means that a small change in blood levels can induce profound toxicity

6

Who is susceptible to drug-drug interactions?

-multiple medications
-elderly
-young
-critically ill
-surgical patients

7

What conditions can increase the likelihood of having a drug-drug interaction?

-liver disease
-renal impairment
-diabetes mellitus
-epilepsy
-asthma

8

What are the 3 mechanism of drug-drug interactions?

-Pharmaceutical
-Pharmacokinetic (absorption, distribution, metabolism, elimination)
-Pharmacodynamic

9

What kind of pharmacodynamics interactions can take place?

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

10

What are the mechanisms of absorption reactions?

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

11

What do most interactions of drugs in the GIT result in?

changes in absorption rather than the extent of absorption

12

When is delayed absorption important?

when a drug has a short half life or when we want high plasma levels rapidly

13

What drugs bind together in the GIT??

-tetracycline and erythromycin complex with Fe, Ca and Mg
-cholestyramine resin can bind to warfarin and digoxin

14

How does pH affect absorption?

-absorption is affected by the degree of ionisation which is dependent on pH
-H2 antagonists, proton pum blockers and antacids reduce H+ and so increase the pH

15

What may lead to the failure of the OCP or digoxin toxicity?

-broad spectrum antibiotics destroy normal gut flora

16

Where are most oral medicines absorbed?

small intestine

17

What is the rate limiting step in drug absorption?

gastric emptying

18

What drugs increase/decrease gastric emptying?

-decrease: anticholinergics, tricyclic anti-depressants, opiates
-increase (domperidone, metoclopramide)

19

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.

20

What is the result of displacement of a drug from plasma protein?

increased bioavailability as only the unbound drug is pharmacologically active

21

What are the 2 most important proteins in protein binding?

-albumin
-a1-glycoprotein

22

How are some patients protected by interactions?

increased metabolism and excretion

23

When do drug interactions involving metabolism occur?

when one drug induces or inhibits the metabolism of another

24

Where does metabolism commonly occur?

in the liver via the cytochrome P450 system

25

What drugs inhibit the cytochrome system?

-clarithromycin
-erythromycin
-CCBs
-omeprazole
-ketoconazole

26

What are potent induced of cytochrome P450?

-barbiturates
-carbamazepine
-phenytoin
-rifampicin
-tobacco

27

How can the metabolism of ciclosporin be increased?

-rifampicin induces CYP3A4
-St John's Wort induces CYP3A4

28

How are most drugs excreted?

in urine or bile

29

How are digoxin and lithium eliminated?

by the kidney

30

What drugs inhibit excretion?

verapamil/diltiazem and digoxin

31

What drugs increase tubular reabsorption?

loop diuretics and lithium

32

When do pharmacodynamics interactions occur?

when the pharmacodynamics actions of a drug either acting directly on the same receptor or indirectly on different receptors

33

How can pharmacodynamics interactions be described?

-direct
-indirect
-antagonistic
-synergistic/agonistic

34

Pharmacodynamic interactions: direct antagonism

beta blockers such as atenolol will block the actions of agonist e.g bronchodilators (salbutamol)

35

Pharmacodynamic interactions: synergistic interaction

when two drugs with the sam epharmacological effect acting on the same receptor are given concurrently

36

Pharmacodynamic interactions: indirect agonism

-CNS depression
benzodiazepines and tricyclics or alcohol
-warfarin and NSAIDs
-atenolol and verapamil

37

Pharmacodynamic interactions:

-NSAIDs and antihypertensive medication
-NSAIDs and treatment for heart failure

38

How to deal with an interaction

If the altering dose timing or no alternative doesn't solve the issue adjust drug dosage +/- monitor drug level (TDM) and physiological functions