Drug absorption and distribution

Question 1

what is absorption of a drug?

Answer 1

how the drug enters the body into general circulation

Question 2

what is distribution of a drug?

Answer 2

transport of the drug by the general circulation, diffusion in the tissues

Question 3

what is metabolism of a drug?

Answer 3

process by which enzymes catalyse the conversion of a lipid soluble drug into a less active and more polar form that is more readily excreted from the body

Question 4

where are most drugs metabolised?

Answer 4

liver

Question 5

what is excretion of a drug?

Answer 5

process that removes the drug from the body

Question 6

what is elimination of a drug?

Answer 6

linked process of metabolism and excretion

Question 7

how does solubility control drug absorption?

Answer 7

drug must dissolve to be absorbed. Higher rate of diffusion with higher lipid solubility.

Question 8

how does chemical stability control drug absorption?

Answer 8

some drugs are destroyed by gut acid, can be modified to release active drug in the gut

Question 9

what is the lipid to water partitian coefficient?

Answer 9

The ratio of the drug concentration in the membrane and the concentration in water at equilibrium.

Question 10

how does degree of ionisation control drug absorption?

Answer 10

only unionised forms diffuse across the lipid bilayer.
Acidic drugs become less ionised in an acidic environment -> can be absorbed in stomach
Basic drugs become less ionised in a basic environment -> absorbed in the small intestine

Question 11

where does the majority of absorption occur?

Answer 11

in the small intestine

Question 12

what factors affect gastrointestinal absorption? 6

Answer 12

GI motility
pH at absorption sites
blood flow at stomach and intestines
how a drug is manufactured
physicochemical interactions
presence of transporters in the membrane

Question 13

what is GI motility?

Answer 13

the rate of stomach emptying and movement through the intestines. Can be modified by drugs, disease states and the presence of food
- pH at the absorption sites

Question 14

give an example of a physicochemical interaction that affect absorption in the GI

Answer 14

calcium rich foods can alter the rate of absorption of some drugs

Question 15

what is oral availability?

Answer 15

amount in systemic circulation / amount administered

Question 16

what is systemic availability?

Answer 16

amount in systemic circulation / amount absorbed

Question 17

drugs administered intra-venously have what % systemic availability?

Answer 17

100%

Question 18

what is first pass or presystemic metabolism?

Answer 18

inactivation of drug by enzymes in the gut wall and liver before reaching systemic circulation and body tissues after oral ingestion.

Question 19

what does enteral drug administration mean?

Answer 19

Administering the drug into the body through the GI tract

Question 20

what does parenteral drug administration mean?

Answer 20

a route that is not via the GI tract

Question 21

learn these roots of drug administration advantages and disadvantages