IDA 2 - Pharmacokinetics: Factors influencing drug action

Question 1

Define pharmacokinetics

Answer 1

What the BODY does to the DRUG

Question 2

Define pharmacodynamics

Answer 2

What the DRUG does to the BODY

Question 3

What is Therapeutic Index (TI)?

Answer 3

The range of doses at which a medication is effective without unacceptable adverse events (ratio of dose of drug producing adverse effects to dose producing desired effect)

Question 4

Is a smaller TI harder or easier to dose?

Answer 4

Harder

Question 5

Wy is pharmacokinetics important?

Answer 5

1. To define dosing schedules
2. Predicts how patient conditions could influence dosing
3. Predicts drug-drug interactions

Question 6

What does ADME stand for?

Answer 6

Absorption, Distribution, Metabolism, Elimination

Question 7

Briefly explain the ADME mechanism

Answer 7

1. Medicine ABSORBED into circulation
2. Drug DISTRIBUTED to various tissues
3. Drug METABOLISED
4. ELIMINATED in urine or feces

Question 8

Define bioavailability

Answer 8

The proportion of drug that reaches the systemic circulation as intact drug after administration

Question 9

First pass metabolism happens commonly to what type of medications?

Answer 9

Oral medications

Question 10

What happens to the effect of a drug if it goes through first pass metabolism?

Answer 10

If it goes through first pass metabolism by the liver before it reaches circulation, the effect of the drug on the body is reduced

Question 11

Why is it important to know about the distribution of a drug?

Answer 11

1. To know if the drug will get to its site of action
   2.To know if drug will cause unwanted effects in other parts of the body

Question 12

Name 4 factors affecting movement/absorption/distribution of a drug

Answer 12

1. Size (smaller molecules cross membranes easier)
2. Lipophilicity (lipid soluble drugs cross cell membranes easier)
3. Degree of ionisation (harder for charged molecules to pass through membrane)
4. Binding to plasma proteins

Question 13

What does an ionised drug mean?

Answer 13

Charged, low lipid solubility

Question 14

What does an unionised drug mean?

Answer 14

Uncharged, good lipid solubilty

Question 15

Bases are ionised in…

Answer 15

Acidic conditions

Question 16

Acids are ionised in…

Answer 16

Basic conditions

Question 17

Define pKa

Answer 17

It is the acid dissociation constant

Question 18

If pKa of drug = 4 and environment is pH 5, the drug is…

Answer 18

The drug is more acidic than the environment and is in a “basic” environment.

Question 19

What does it mean if pKa = pH of environment?

Answer 19

The drug is 50% ionised and 50% unionised

Question 20

What happens when a drug binds to plasma proteins?

Answer 20

The plasma bound drug is confined to the vascular compartment
- cannot interact with target
- cannot exit plasma, therefore NOT WORKING
It has little effect on body but INCREASES duration in the body

Question 21

What are the 3 options for drug movement?

Answer 21

1. Stay in the vasculature
2. Move out to extracellular space
3. Enter cells

Question 22

Define Volume Of Distribution (Vd)

Answer 22

The volume into which a drug appears to be distributed with a concentration equal to that of plasma.

Vd = dose/ [drug in plasma]