Drug interactions

Question 1

What is clearance?

Answer 1

rate of drug elimination/ drug plasma conc
(efficiency of irreversible elimination of a drug from systemic circulation)

Question 2

What is a drug interaction?

Answer 2

when a substance alters the expected performance of a drug
- substance: drug, food, toxin

Question 3

What is a pharmacodynamic drug interaction?

Answer 3

Occur when drugs have an effect on the same target or physiological system

Question 4

What is a pharmacokinetic drug interaction?

Answer 4

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

Question 5

What are the 2 types of pharmacodynamic drug interactions?

Answer 5

Synergistic or antagonistic

Question 6

What is summation?

Answer 6

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

Question 7

What is potentiation?

Answer 7

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 8

What are some risk factors for drug interactions?

Answer 8

● Narrow therapeutic index
● Steep dose/response curve
● Saturable metabolism

Question 9

What is synergy?

Answer 9

interaction of drugs such that the total effect is greater than the sum of the individual effects (work together)

Question 10

What is antagonism?

Answer 10

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

Question 11

How can a drugs absorption be affected?

Answer 11

1. Drugs which alter pH of GI tract
2. Formation of insoluble drug complexes
3. P-glycoprotein induction/inhibition
4. Motility

Question 12

Describe how motility can affect drug absorption

Answer 12

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

Question 13

Describe how pH affects absorption of drugs

Answer 13

• Changes in pH will alter the proportion of ionised and unionised drug
• Changes in gastric pH

Question 14

How do is absorption affected by drug interactions?

Answer 14

One drug affects the rate or extent of absorption of another drug

Question 15

Describe how formation of insoluble drug complexes affect drug absorption

Answer 15

Insoluble drug complexes will not be absorbed and will be retained in the GIT

Question 16

Describe how P-glycoprotein induction/inhibition affects drug absorption

Answer 16

• P-glycoproteins (P-gp) are drug transporter proteins widely distributed in body
• Excretory function to remove toxic substances (incl drugs) out of cells
• Activity can be altered by Pgp inhibitors and inducers leading to increased or decreased level of Pgp substrates
  (more Pgp can remove some drugs)

Question 17

How can distribution affect a drugs absorption?

Answer 17

• Interactions can occur when drugs compete for protein binding
• 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 18

What are CYP450?

Answer 18

Haemoproteins

Question 19

What can inhibitions of CYP450 do?

Answer 19

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

Question 20

What can induction of CYP450 do?

Answer 20

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

Question 21

What does renal excretion depend on?

Answer 21

pH

Question 22

What conditions are weak bases cleared faster in?

Answer 22

Acidic urine

Question 23

What conditions are weak acids cleared faster in?

Answer 23

Alkali urine

Question 24

Which drug has a lot of drug interactions?

Answer 24

Warfarin

Question 25

What drugs could cause acute kidney injury?

Answer 25

NSAIDs, ACEi (ACE inhibitors)

Question 26

Which drug is highly protein bound?

Answer 26

Warfarin