CEP WK3 - DRUG ABSORPTION/DISTRIBUTION

Question 1

1-COMPONENT MODEL OF PHARMACOKINETICS

Answer 1

assumes body is one big vessel & the log conc/time curve goes up instantly then you see it level off evenly as it leaves body

Question 2

AVD (apparent volume of distribution)

Answer 2

AVD = dose/ plasma conc. (low AVD = high volume of drug in blood)

Question 3

2-COMPONENT MODEL OF PHARMACOKINETICS

Answer 3

main component is plasma but also has another one for slow phase (lots distributed out in fast phase from compartment 1 (quick drop in conc) & then compartment 2 slowly refills it to be released) (graph is fast rise then slow drop)

Question 4

FACTORS AFFECTING DRUG ABSORPTION

Answer 4

blood flow, lipid solubility, diffusion barriers, tissue barrier, time available for digestion

Question 5

METABOLISM OF DRUG

Answer 5

first pass metabolism in liver & then adding sulphate to destroy the drug (what the OH- is added to)

Question 6

CYTOCHROME P450

Answer 6

heme iron in p450 usually in Fe3+ state but when reduced to Fe2+ state it can bind ligands

Question 7

FIRST PASS METABOLISM

Answer 7

P450 enzyme introduces hydroxyl groups to make compounds more hydrophilic then these charged OH- groups linked to other compounds to be more hydrophilic (to form excretable watery solution)

Question 8

EFFICACY

Answer 8

maximum response achievable from a drug

Question 9

POTENCY

Answer 9

how much drug needed to produce effect

Question 10

0 ORDER KINETICS

Answer 10

constant amount of drugs lost per time

Question 11

1 ORDER KINETICS

Answer 11

drug loss proportional to drug concentration

Question 12

HOW WE INFLUENCE ABSORPTION

Answer 12

• particle size (powder = quick)
• enteric-coated capsules (semi-permeable membrane of capsule so water drags out drug)
• pump system for slower release

Question 13

FACTORS AFFECTING SKIN ABSORPTION

Answer 13

• skin thickness/damage
• hydration
• blood flow
• lipid solubility

Question 14

ION TRAPPING

Answer 14

• only unionised form (AH) in equilibrium (A- + H+ -> AH) is lipid-soluble so diffuses through membrane & ions trapped in new side as ions reformed (AH -> A- + H+) as drugs accumulate where ionisation is favoured
• drug with higher pH (weaker base) has lower conc in circulation
• no enzyme or energy needed as relies on membrane semi-permeability
• is why basic drugs secreted to acidic stomach & acidic drugs excreted in alkaline urine