Session 7: Pharmacokenetics

Question 1

What are the 2 ways in which drugs are taken into the body?

Answer 1

Adsorption

Distribution

Question 2

What are the 2 ways in which drugs are removed from the body?

Answer 2

Metabolism

Elimination

Question 3

What is enteral administration?

Answer 3

Delivery into the internal environment of the body i.e. the GI tract

1. Oral
2. Sublingual
3. Rectal

Question 4

What is parenteral administration?

Answer 4

Delivery via all other routes that aren’t the GI tract

1. Intravenous
2. Subcutaneous
3. Intramuscular

Question 5

TRUE OR FALSE: There is little adsorption in the stomach.

Answer 5

True:)

Question 6

Where does the majority of adsorption take place?

Answer 6

Small intestine

Question 7

Name 2 ways in which drugs can be absorbed.

Answer 7

1. Passive Diffusion

2. Facilitated diffusion

Question 8

What sort of drugs are adsorbed by passive diffusion?

Answer 8

Lipophilic drugs that are weak acids/bases which diffuse directly down their concentration gradients

Question 9

What sort of drugs are adsorbed by facilitated diffusion?

Answer 9

OATs (organic anion transporters) and OCTs (organic cation transporters) are solute carrier proteins (SLC) that transport molecules with nett charges

Question 10

Name 3 physiochemical factors affecting drug absorption.

Answer 10

1. GI length/SA
2. pKa of drug
3. Density of SLC expression

Question 11

Name 3 GI physiology factors affecting drug absorption.

Answer 11

1. Blood flow
2. GI motility
3. Food iPh

Question 12

What is meant by first pass metabolism?

Answer 12

It is a phenomenon of drug metabolism whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation.

Question 13

What are the 2 main enzyme groups that are responsible for first pass metabolism by the GI and the Liver?

Answer 13

1. Cytochrome P450s - Phase I enzymes

2. Conjugating - Phase II enzymes

Question 14

Where is their larger expression of Phase I and phase II enzymes?

Answer 14

The liver

Question 15

What is bioavalibility?

Answer 15

Fraction of a defined dose which reaches its way into a specific body compartment.

Question 16

How is Oral Bioavailibility (F) calculated?

Answer 16

Amount reaching systematic circulation/total drug given IV (calculate the area under the curves) which gives a result between 0 and 1

Question 17

How can a drug reservoir in the body be established?

Answer 17

Drugs may bind to plasma and/or tissue proteins decreasing the drug availability for binding.

Question 18

What is apparent volume of distribution? (Vd)

Answer 18

A model used to provide a summary measure of drug molecule behaviour during distribution.

(Summarises movement out of plasma -> interstitial -> intracellular compartment)

Question 19

What can be implied by a small Vd value?

Answer 19

less penetration of interstitial/ intracellular fluid compartment

Question 20

How many superfamilies of cytochrome P450 enzymes are there?

Answer 20

3 (they do not show overlap)

Question 21

Name 5 factors affecting drug metabolism.

Answer 21

1. Age
2. Sex
3. disease (i.e. especially hepatic renal CVS
4. drugs which inhibit or induce CYP450s
5. CYP450 polymorphism (genetic variation)

Question 22

What is clearance? (CL)

Answer 22

The rate of elimination of a drug from the body

Question 23

What is the sum for clearance? (CL)

Answer 23

Hepatic clearance + Renal clearance

Question 24

What is drug half life? (t1/2)

Answer 24

The amount of time over which the concentration of a drug in plasma decreases to one half of its value of when it was first measured.

Question 25

What is meant by first order (linear) elimination kinetics?

Answer 25

The rate of metabolism is proportional to the concentration of the drug.

Question 26

What are the conditions of first order (linear) kinetics?

Answer 26

• Plenty of phase I/II enzymes

- Plenty of OCTs/ OATs

Question 27

What happened when an elimination process becomes saturated?

Answer 27

The rate becomes limited (referred to as zero order kinetics)