Pharmacology

Question 1

What is absorption?

Answer 1

Process by which drug enters the body from it’s site of administration and enters general circulation
(lumen of GI tract not in body)

Question 2

What is distribution?

Answer 2

Transport of drug by general circulation

Question 3

What is metabolism?

Answer 3

Process by which enzymes (often in liver) catalyze the breakdown of drugs usually into less active, more polar forms which can be excreted more easily

(more polar mean more difficult to enter cell)

Question 4

What is excretion?

Answer 4

Processes which remove drug from body

often involves kidneys but other routes exist

Question 5

What are the physicochemical factors which control drug absorption in the GI tract?

Answer 5

Solubility - must be water-soluble to be absorbed

Chemical stability - some drugs degraded by acid in stomach / enzymes in GI tract

Lipid to water partition coefficient - ratio of drug conc in membrane and water at equilibrium

Degree of Ionisation - low degree means drug is easier to absorb than a high degree due to ionic character

Question 6

What is the pKa?

Answer 6

pH at which half of drug is ionised and half is unionised

Question 7

What affects the degree of ionisation of a drug?

Answer 7

pKa and pH

Question 8

What is the Henderson-Hasselbach equation?

Answer 8

pH - pKa = log (A-/AH)

pH - pKa = log (B/BH+)

Question 9

When do weak acids have a low degree of ionisation?

Answer 9

When in an acidic environment

Question 10

When do weak bases have a low degree of ionisation?

Answer 10

When in a basic environment

Question 11

Where are weak acids and bases mostly absorbed?

Answer 11

Small intestine

Although weak acids are also absorbed in stomach

Question 12

What kind of acid and base is not easily absorbed by the body?

Answer 12

Strong acids and bases due to their strong ionic character

Question 13

What can affect GI absorption?

Answer 13

GI tract motility - rate at which stomach empties and intestines move

pH at site of absorption (varies in GI tract)

Blood flow to area

Design of delivery ie releases in certain conditions/places

Physicochemical interactions with other food

Transporter proteins in cell membranes

Question 14

What can alter GI tract motility?

Answer 14

Drugs
Disease states
Presence/absence of food

Question 15

What is oral availability?

Answer 15

Fraction of drug which reaches systemic circulation having been taken orally

Oral availability = amount in systemic circulation/amount taken

Question 16

What is systemic availability?

Answer 16

Fraction of drug which reaches systemic circulation after absorption

Systemic availability = amount in systemic circulation / amount absorbed

Question 17

What are the enteral routes of drug administration?

Answer 17

Enteral routes - via GI tract

Oral (PO - per os)
Sublingual Buccal
Rectal (PR - per rectum)

Question 18

What are the parenteral routes of drug administration?

Answer 18

Parenteral - NOT via GI tract

Intravenous
Intramuscular (IM)
Subcutaneous (SC)
Transdermal
Inhalational
Topical (TOP)

Question 19

What is Vd?

Answer 19

The volume of distribution, this is the volume in which a drug appears to have been absorbed

Question 20

What is the Vd for a drug administered intravenously?

Answer 20

Vd = dose / plasma concentration

v = n/c

Question 21

What does it mean if Vd < 10 litres?

Answer 21

Drug is mostly dissolved in vascular compartment

Question 22

What does it mean if 10 litres < Vd < 30 litres?

Answer 22

Drug mostly in extracellular water

Question 23

What does it mean if Vd > 30 litres?

Answer 23

Drug mostly in specific tissues or distributed throughout all water in body