Drug Absorption and Distribution

Question 1

Pharmacodynamics:

Answer 1

what drug does to body, characterised by affinity, potency, efficacy by calculating K, EC50, EMAX

Question 2

Pharmacokinetics

Answer 2

what the body does to drug

Question 3

• Absorption:

Answer 3

drug is absorbed from site of administration into circulation
- entry into plasma

Question 4

Distribution:

Answer 4

drug reversibly leaves bloodstream, distributed into intracellular fluids

Question 5

Metabolism:

Answer 5

drug transformation by metabolism - liver and other tissues

Question 6

Excretion (elimmination):

Answer 6

drug and/or drug metabolites excreted in urine, faeces or bile

Question 7

Passive diffusion

Answer 7

• Small, lipid soluble, non-polar Drugs
• High concentration gradient
• Directly through lipid/aquaporins

Question 8

Facilitated diffusion

Answer 8

Larger, water-soluble drugs, polar drugs
- Can show saturation kinetics: limited amount of carriers
- Drug may accumulate in compartments
- may show adverse effects if drug is susceptible to saturation kinetics

Question 9

Active transport

Answer 9

• Transported against concentration gradient
• Requires carrier proteins w ATP
• Water-soluble drugs
• Can show saturation kinetics

Question 10

Blood brain barrier:

Answer 10

brain and blood vessels supplying brain have tight junctions which regulate molecules entering brain

Question 11

Endocytosis

Answer 11

• Bulk low (large molecules) through circulatory system
• Invagination of cell membrane where drug is encased in vesicle and released inside cell

Question 12

what does the degree of ionisation depend on

Answer 12

pKa of drug and local pH

Question 13

pKa:

Answer 13

pH at which 50% of drug is ionised and 50% is unionised

Question 14

what is the Henderson-Hasselbalch equation used to determine

Answer 14

proportions of ionised and unionised drugs in a given pH environment

Question 15

pH trapping

Answer 15

• Drugs are trapped in compartments that have particular pH
• Occurs as diff compartments have diff pH which tolerate drugs differently

Question 16

Weak bases:

Answer 16

better abosrbed in acidic environment

Question 17

Weak acids:

Answer 17

better abosrbed in alkaline environement

Question 18

Non-polar drugs:

Answer 18

can easily cross membrane to be metabolised (as they are lipophillic)

Question 19

Drug distribution

Answer 19

1. Mouth
2. Walls of small intestine
3. Trasnported to liver by portal vein

Question 20

Vd:

Answer 20

extent to which drug spreads between plasma and tissue compartments

Question 21

Low Vd:

Answer 21

drugs retained in vascular compartments - mostly in plasma

Question 22

High Vd:

Answer 22

drugs retained in non-vascular compartments – adipose, muscle etc.

Question 23

Determining Vd

Answer 23

1. Administer dose
2. Obtain blood sample
   
   • Seperate plasma from RBC
3. Assay for concentration of drug plasma [drug]plasma
4. Calculate Vd using Vd = Dose/[drug]plasma

Question 24

Albumin:

Answer 24

most abundant plasma protein, high affinity for hydrophobic drugs