Pharmacokinetics

Question 1

What are the 4 stages a drug goes throug in the body?

Answer 1

Absorption
Digestion
Metabolism
Excretion

Question 2

What 2 ways to drug molecules move around the body?

Answer 2

Bulk flow (Blood, lymph, CSF)
Diffusion

Question 3

List the 4 ways small molecules cross cell-membranes

Answer 3

Passive diffusion (through lipid)
Diffusion through aqueous pores
carrier mediated transport
Pinocytosis (fluid endocytosis0

Question 4

Are acids more ionised in high or low pH?

Answer 4

High pH

Question 5

What is pKa?

Answer 5

Negative log of the acid dissociation constant

Question 6

What is the henderson-hassalbach equation?

Answer 6

pH = pKa + log (base/acid)

Question 7

Do strong acids have a high or low pKa?

Answer 7

Low pKa

Question 8

Do weak acids have a high or low pKa?

Answer 8

High pKa

Question 9

What happens to the drug if the pH on either side of the cell membrane ?

Answer 9

Concentration of ionised to unionised will also be equal

Question 10

What happens to an acidic drug if the pH is not equal on either side of the cell membrane?

Answer 10

Acidic drug higher conc on higher pH side

Question 11

What happens to an basic drug if the pH is not equal on either side of the cell membrane?

Answer 11

basic drug, higher conc on lower pH side

Question 12

Give 3 sites where carrier mediated transport is important?

Answer 12

BBB
GI tract
Renal tube

Question 13

What are the 2 main processes involved in carrier mediated transport?

Answer 13

facilitated transport 
active transport  (ATP)

Question 14

What are the 7 routes of drug administration?

Answer 14

Oral 
Sublingual 
Rectal 
Topical application (skin, eye)
Inhalation 
Transdermal 
Injection

Question 15

What are the 5 types of injection for drug administration?

Answer 15

subcutanous (under skin)
IV
IM 
Intrathecal (spinal canal)
intravitreal (into eye)

Question 16

Give two examples of unstable drugs in an environment

Answer 16

-penicillin unstable in low pH

Insulin unstable in presence of digestive enymes

Question 17

Define Bioavailability (F)

Answer 17

the fraction of the administered dose that reaches systemic circulation as the parent drug

Question 18

Why does F not equal 1 for orally administered drugs?

Answer 18

• tablet not release all contents
• molecule too polar to be absorbed
• first pass metabolism in gut lumen

Question 19

What is first pass metabolism?

Answer 19

where the concentration of the drug is greatly reduced before it reaches systemic circulation

Question 20

What is percataneous administration?

Answer 20

• across the skin

- limited effect

Question 21

What’s a benefit of intranasal administration?

Answer 21

• nasal mucosa has good SA for absorption

- few drug-metabolising enzymes

Question 22

What is a benefit of rectal administration?

Answer 22

• avoids first pass metabolism
• good absorption
• patients who are vomiting

Question 23

What is a pro-drug?

Answer 23

A drug that is metabolised after admin to a pharmacologically active metabolite

Question 24

Example of a pro-drug;

Answer 24

Codeine, metabolised by CYP2D6 in liver to morphine

Question 25

Define volume of distribution

Answer 25

the volume of plasma that would be necessary to account for the total amount of drug in the patient’s body, if that drug were present throughout the body at the same concentration as found in the plasma.

Question 26

What does a low Vd mean?

Answer 26

Drug remains in a few organs and circulation

Question 27

What does a high Vd mean?

Answer 27

Distributed into all compartments

Question 28

Where does drug metabolism mainly occur?

Answer 28

in the liver by CYP450 enzymes

Question 29

What is phase 1 metabolism?

Answer 29

(usually) an oxidative step
polar functional group is added
e.g. hydroxyl group

Question 30

What is phase 2 metabolism?

Answer 30

Involves conjugation of phase 1 metabolite and endogenous compound

Question 31

Give 4 sites where first pass metabolism can occur

Answer 31

Intestinal lumen
Intestinal wall
liver
lungs

Question 32

Give 3 examples of drugs that undergo significant first pass metabolism

Answer 32

L-DOPA
Aspirin
Lidocaine

Question 33

What does high therapeutic index mean and give an example?

Answer 33

Low risk of toxicity e.g. Diazepam

Question 34

What does low therapeutic index mean and give an example?

Answer 34

High risk of toxicity e.g digoxin

Question 35

What is enterohepatc circulation?

Answer 35

Molecules in the bile secreted by the liver , moved to the duodenum where they are reabsorbed and transported back to the liver

Question 36

What are the 3 processes involved in urine secretion?

Answer 36

1. Glomerular filtration
2. Reabsorption
3. Tubular secretions

Question 37

What is first order kinetics?

give an example

Answer 37

rate of reaction proportional to amount of substrate available

e.g. metabolism

Question 38

What is zero order kinetics?

give an example

Answer 38

change in conc with time is at a fixed rate, independent of concentration

e.g. metabolism of ethanol

Question 39

Define half life

Answer 39

The time taken for the plasma conc/ amount of drug in the body to half

Question 40

Define Clearance

Answer 40

The rate at which the volume of plasma cleared of an active drug per unit of time

Question 41

What is the effect of a high Vd on half life?

Answer 41

high Vd, large fraction of drug in tissues, less accessible to organs of elimination = longer half life

Question 42

Generally, when is steady state reached?

Answer 42

every 4-5 half lives