Drug Interactions

Question 1

Synergy definition

Answer 1

Interactions of drugs such that the total effect is greater than the sum of the individual effects
(1+1>2)
E.g. codiene and paracetamol

Question 2

Antagonism defintion

Answer 2

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

Question 3

Summation definition

Answer 3

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

Question 4

Potentiation defintion

Answer 4

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 5

Pharmacodynamics defintion

Answer 5

The effect the drug has on the human body

Question 6

Pharmacokinetics

Answer 6

What the body does with the drug (disposition of a compound within an organism)
Absorption, Distribution, Metabolism and Excretion (ADME)

Question 7

Risk factors of pharmacotherapy

Answer 7

Narrow therapeutic index
Steep dose/response curve
Saturable metabolism

Question 8

4 Mechanisms of pharmacokinetics

Answer 8

Absorption
- route and entry into body
- bioavailability - how fast and to what extent drug reaches systemic circulation
= IV = always 100%
= Oral = less than 100% due to first pass metabolism
Distribution
- drug distributed in plasma according to CHEMICAL PROPERTIES + SIZE. May be up-taken by some organs (liver, brain)
Metabolism
- drug metabolised in KIDNEYS or LIVER
- kidney = mostly small water soluble
- liver = hydrophobic molecules
Excretion
- in urine + faeces

Question 9

What is absorption in pharmacokinetics

Answer 9

Motility - if he gut has slowed digestion, the drugs wont work as well (oral contraceptive pill and antibiotics is the most common interaction)
Acidity - pH and pKa interactions
Solubility
Complex formation

Question 10

What is distribution of pharmacokinetics?

Answer 10

Drugs can go into proteins, other tissues or the effect site
- protein binding = if you give 2 highly protein bound designs, they will make each other strong and increase their effect so you will always make sure you know what drugs the patients has taken before giving them new drugs

Question 11

What is metabolism in pharmacokinetics

Answer 11

CYP450
- Haemoproteins
- Metabolise many substances - endogenous and exogenous
Inhibition
- Drug A blocks metabolism of drug B, leaving more free drug B in the plasma so it has an increased effect
Induction
- Drug C induced CYP450 isoenzyme leading to increased metabolism of drug D so it has decreased effect
Excretion
- Renal
= pH dependant
= weak bases - cleared faster if urine acidic
= weak acids - cleared faster if urine alkali
- biliary (minor)

Question 12

3 Mechanisms of pharmacodynamics

Answer 12

Receptor based
- agonists
- partial agonists
- antagonists
= competitive
= non-competitive
Signal transduction
- rare
Physiological systems
- different drugs that effect different receptors, but in the same physiological system

Question 13

Drug interactions to be aware of

Answer 13

Warfarin
Drugs involved in AKI - NSAIDS, ACE-I