drug interactions

Question 1

define clearance (CL)

Answer 1

The rate of drug elimination/drug plasma conc

Efficiency of irreversible elimination of a drug from systemic circulation

Question 2

what can drug interactions lead to

Answer 2

adverse drug reactions (ADRs)

Question 3

3 guidelines for prescribers

Answer 3

avoid co prescribing drugs with clinically significant interactions

appropriately monitor patients taking interacting drugs

recognise drug interactions and take appropotate action

Question 4

what are the 2 types of drug-drug interactions

Answer 4

pharmacokinetic and pharmacodynamic

Question 5

define drug interaction

Answer 5

occurs when a substance alters the expected performance of a drug

Question 6

define pharmacodynamic

Answer 6

occur when drugs have an effect on the same target or physiological stem

the effect the drug has on the human body

Question 7

define pharmacokinetic

Answer 7

occur when a drug affects the pharmacokinetics ( absorption, distribution, metabolism or excretion) of another drug

what the body does with the drug (the disposition of a compound within an organism)

Question 8

what are the 4 types of pharmacodynamic interactions

Answer 8

1. synergistic
2. antagonistic
3. summation
4. potentation

synergistic - work together

antagonistic - cancel each other out

Question 9

what kind of drugs are less problematic

Answer 9

highly selective drugs

Question 10

describe synergy

Answer 10

interaction of drugs such that the total effect is greater than the sum of the individual effects (1+1>2)

Question 11

describe antagonism

Answer 11

an antagonist is a substance that acts against and blocks an action (2 drugs opposed to each other) (1+1=0)

Question 12

describe summation

Answer 12

different drugs used together to have the same effect as a single drug would (1+1=1)

Question 13

describe potentaion

Answer 13

enhancement of one drug by another so that the combined effect is greater than the sum of each one alone (1+1=1+1.5)

Question 14

are drug interactions only positive

Answer 14

no
Drug interactions can be positive or negative.

Question 15

3 risk factors for drug interactions

Answer 15

Narrow therapeutic index
Steep dose/response curve
Saturable metabolism

Question 16

4 mechanism steps for pharmacokinetics

Answer 16

Absorption, Distribution, Metabolism, Excretion

Question 17

what 4 things affect absoprtion

Answer 17

Motility

Acidity

Solubility

Complex formation

Question 18

how does motility affect absoprtion

Answer 18

if the gut has slowed digestion, the drugs won’t work as well (oral contraceptive pill and antibiotics is the most common interaction)

Question 19

how does acidity affect absoroption

Answer 19

pH and pKa interactions.

Question 20

3 ways the drug can distribute

Answer 20

can go into the proteins, other tissues or the effect site

Question 21

describe protein binding

Answer 21

If you give 2 highly protein bound drugs, they will make each other strong and increase their effect so you always make sure you know what drugs the patient has taken before giving them new drugs

Question 22

what 4 things affect metabolism

Answer 22

CYP450
inhibition
induction
excretion

Question 23

impact of CYP450

Answer 23

Haemoproteins
Metabolise many substrates – endogenous and exogenous

Question 24

what is inhibition

Answer 24

Drug A blocks metabolism of drug B, leaving more free drug B in the plasma so it has an increased effect

Question 25

what is induction

Answer 25

Drug C induced CYP450 isoenzyme leading to increased metabolism of drug D so it has a decreased effect

Question 26

what is excretion

Answer 26

Renal
- pH dependant
- Weak bases – cleared faster if urine is acidic
- Weak acids – cleared faster if urine alkali

Billary (minor)

Question 27

3 mechanisms for pharmacoydnamics

Answer 27

Receptor based

Signal transduction

Physiological systems

Question 28

describe receptor based

Answer 28

Agonists
Partial agonists
Antagonists
Competitive
Non-competitive

Question 29

describe signal based

Answer 29

its rare

Question 30

describe physiological systems

Answer 30

Different drugs that effect different receptors, but in the same physiological system

Question 31

2 drug interactions to be aware of

Answer 31

Warfarin – lots of interactions – enzyme induction

Acute kidney injury – NSAIDs, ACEi