Drug to drug interactions

Question 1

what is the definition of a drug to drug interaction?

Answer 1

A drug interaction has occurred when the pharmacological effect of two or more drugs given together is not just a direct function of their individual effects ie the outcome of being on multiple drugs

Question 2

what types of drug- drug interactions are there?

Answer 2

drug- drug 
herbal-drug
food- drug
drink-drug
pharmacogenetic interactions (caused by genetic differences)

Question 3

what is the ‘object drug’

Answer 3

the drug whose activity is effected by such an interaction

Question 4

what is the precipitant?

Answer 4

the agent which causes a drug- drug interaction. ie the drug that once administered results in reaction with object drug

Question 5

what are some non-detrimental drug interaction outcomes?

Answer 5

treating hypertension (high BP)
treating Parkinsonism

Question 6

define polypharmacy

Answer 6

loose definition but usually means being on 4 or more drugs

Question 7

what type of drug is warfarin?

Answer 7

an anticoagulant

Question 8

name some drugs involved with serious interactions

Answer 8

lithium
digoxin
warfarin
theophylline (asthma) 
OCP- oral contraceptives
gentamicin- anti bacterial
erythromicin- pnuemonia, acne
neuroleptics- anti psychotics

Question 9

what would Digoxin do if you took it

Answer 9

may slow your heart rate down

Question 10

what is so dangerous about drugs that cause serious drug to drug interactions

Answer 10

they are potent drugs with a narrow therapeutic index ie doesn’t take much to become toxic or ineffective- small change in blood levels can induce profound toxicity

Question 11

therapeutic drug monitoring?

Answer 11

checking for plasma levels of a drug to make sure the levels are within the correct range

Question 12

who are susceptible to serious drug interactions?

Answer 12

those who are already on a number of medications are at a high risk
also the elderly, young, critically ill and patients undergoing complicated surgical procedures, those with chronic conditions

Question 13

which chronic conditions can put patients at higher risk of serious drug interactions

Answer 13

liver disease
renal impairment
epilepsy
asthma

Question 14

why are adolescents less likely to have serious drug to drug interaction?

Answer 14

more likely to have a good physiology

Question 15

which things can one drug alter in another drug

Answer 15

Absorption
distribution
metabolism
elimination of another drug

Question 16

changes in GI bacterial flora?

Answer 16

bacterial flora usually found in the large bowel and a broad spectrum of antibiotics destroy the normal gut flora.
This may lead to failur of oral contraceptive or digoxin toxicity

Question 17

which drugs does Cholestyramine resin bind to in the GI tract?

Answer 17

warfarin and digoxin

Question 18

which 3 things reduce H+ and so increase pH of blood?

Answer 18

H2 antagonists, proton pump blockers and anti acids

Question 19

protein-binding displacement?

Answer 19

occurs when there is a reduction in the extent of plasma protein binding of a drug caused by the presence of another drug- results in increased bio-availability of the displaced drug (only unbound drugs are pharmacologically active)

Question 20

what are the two most important proteins involved in drug binding?

Answer 20

albumin

alpha1-glycoprotein

Question 21

Drugs that are very highly protein bound

Answer 21

diazepam
ibuprofen
Valproic acid- not to be used in females of child bearing age
warfarin

Question 22

drug interactions involving metabolism occur when?

Answer 22

when one drug induces or inhibits the metabolism of another

metabolism

Question 23

where does metabolism usually occur and via which system?

Answer 23

in the liver

via the cytochrome P450 system (a group of enzymes involved in metabolism of drugs)

Question 24

which drugs inhibit the cytochrome P450 system?

Answer 24

erythromicin
clarithromycin
omeprazole
CCBs
cimetidine
ie they inhibit a small group of drugs that are metabolised by cytochrome p450 system

Question 25

which drugs induce the cytochrome P450 system?

Answer 25

phenytoin, tobacco smoke, carbamazepine

enzyme induction causes loss of effect of the drug because you get through the drug more rapidly

Question 26

what do the effects of enzyme induction depend on?

Answer 26

age
disease
genetics
concurrent drug therapy

Question 27

what does Rifampicin do and what does it treat?

Answer 27

increases metabolism of ciclosporin by inducing CYP 3A4

bacterial infections including tb

Question 28

what is st john’s wort

Answer 28

a herbal remedy that can cause rejection of drug ie reduced effect

Question 29

where are digoxin and lithium excreted?

Answer 29

kidney

Question 30

which 2 changes can alter elimination/excretion of a drug

Answer 30

changes in how well the kidney filters waste from the blood (GFR) or tubular secretion

Question 31

pharmacodynamics interactions

Answer 31

occur when what the drug does to the body is changed due to the presence of another drug either acting directly on the same receptor or indirectly on different receptors
like beta blockers or ace inhibitor

Question 32

what are ACE inhibitors?

Answer 32

heart medications that widen, or dilate, your blood vessel- increases the amount of blood your heart pumps and lowers blood pressure.

Question 33

what is a beta blocker?

Answer 33

medications that reduce your blood pressure. Beta blockers work by blocking the effects of the hormone adrenaline. When you take beta blockers, your heart beats more slowly and with less force, thereby reducing blood pressure.

Question 34

what 4 typed of pharmacodynamic interactions are there?

Answer 34

indirect
direct
antagonistic
synergistic/agonistic

Question 35

direct antagonism

Answer 35

beta blockers such as atenolol will block actions of agonists

Question 36

what are synergistic interactions

Answer 36

when two drugs with the same pharmacological effect acting on the same receptor are given concurrently- the effect may be additive or multiplicative (even bigger than the 2 added together)

Question 37

indirect agonism

3 examples and resultant effect

Answer 37

benzodiazepines and tricyclics or alcohol, atenolol

warfarin and NSAIDs

atenolol and verapamil (this could lower heart rate way too much)

all act in different ways but togther have a massive affect on CNS depression

Question 38

2 examples of indirect antagonism

Answer 38

NSAIDs and antihypertensive medication
NSAIDs and treatment for heart failure
NSAIDs lower BP and antihypertensive increases it