Drug absorption and distribution

Question 1

What is pharmokinetics?

Answer 1

The study of the change in drug and metabolite concentrations in tissues and body fluids

Question 2

What is a therapeutic window?

Answer 2

The range of concentrations that allow the drugs to reach their site of action below a toxic concentration

Question 3

What is the therapeutic ratio?

Answer 3

Maximum non-toxic dose
Over
Minimum therapeutic dose

Question 4

What is TD50?

Answer 4

The toxic dose of a drug for 50% of the population

Question 5

What is ED50?

Answer 5

The minimum effective dose for 50% of the population

Question 6

What is the relationship between therapeutic ration and drug safety?

Answer 6

The higher the therapeutic ratio, the safer the drug

Question 7

What are the four parts to pharmokinetics?

Answer 7

Absorption
Distribution
Metabolism
Excretion

Question 8

What is absorption?

Answer 8

Movement of the drug from point of administration to plasma

Question 9

What is distribution?

Answer 9

From plasma to tissues and organs

Question 10

What is metabolism?

Answer 10

Metabolism of drugs by enzymes in the body

Question 11

What is excretion?

Answer 11

Excretion of drug or metabolite by the body

Question 12

Why is ADME important?

Answer 12

Drug development
Understanding toxicity
Establishing route of administration
Establishing drug dose
Understanding possible drug interactions

Question 13

What is the definition of bioavailability?

Answer 13

Fraction of unchanged drug that reaches systemic circulation

Question 14

What is the bioavailability of IV drugs?

Answer 14

100%

Question 15

What is absorption dependent on?

Answer 15

Route of administration
Chemical nature of the compound
Formulation
Blood flow to site of delivery

Question 16

What is formulation?

Answer 16

Tablet or liquid form etc

Question 17

What is the fastest route of administration?

Answer 17

Intravenous

Question 18

What is the slowest form of administration?

Answer 18

Orally

Rectally

Question 19

What are the six possible routes of administration?

Answer 19

Intravenously
Sublingually
Orally
Rectally
Intramuscular
Subcutaneous

Question 20

What is a risk involved with intravenous drug administration?

Answer 20

Infection

Question 21

What is a side effect of intramuscular or subcutaneous drug administration?

Answer 21

Invasive and painful

Can cause local reactions

Question 22

What is a consequence of sublingual administration?

Answer 22

Only a small amount can be absorbed

Question 23

What must be considered when a drug is absorbed in the GI tract?

Answer 23

Its interactions with food
The rate of transit in the gut
pH sensitivity when passing through the stomach

Question 24

What can cross the cell membrane?

Answer 24

Very impermeable to charged molecules
Lipophilic molecules can cross the membrane
Particulates can cross by pinocytosis

Question 25

Where are weak acid and weak base drugs best absorbed?

Answer 25

In their uncharged states In more alkaline conditions, more alkali drugs are absorbed It is the same for acids

Question 26

Where do drugs tend to accumulate?

Answer 26

Where they are ionised as they then can't cross any membranes

Question 27

What is first pass metabolism?

Answer 27

``` Enteral drugs (oral or rectal) have to pass the liver The metabolism of the drugs before they reach systemic circulation is known as first pass metabolism ```

Question 28

What is enterohepatic circulation?

Answer 28

Some drugs entering the gut are absorbed, enter the portal circulation, pass from liver to bile then back to the GI tract

Question 29

What drugs do not distribute?

Answer 29

Large drugs or those that bind to plasma proteins

Question 30

Define drug distribution

Answer 30

How drugs equilibrate within the body after entering the systemic circulation

Question 31

Where may drugs distribute?

Answer 31

``` Not at all Extracellular space Total body water Accumulate in cells Distribute to fat ```

Question 32

What is the volume of distribution?

Answer 32

The volume of fluid required to contain the total amount of drug in the body at the same concentration as that present in the plasma

Question 33

How do you calculate volume of distribution?

Answer 33

Vd = D / Cp ``` D = amount of drug Cp = plasma concentration ```

Question 34

What is the effect of binding to circulation proteins on drug action?

Answer 34

``` e.g. albumin Decreases initial free concentration Slows distribution Slows clearance Prolongs duration of action ```

Question 35

What drugs bind to albumin?

Answer 35

Salicylates (eg aspirin) | Warfarin