L9-10 PHRM20001 Pharmacokinetics

Question 1

What is first pass hepatic metabolism?

Answer 1

Oral administration -> Drug enters hepatic vein -> liver -> amount entering systemic circulation is reduced

Question 2

sc, im, iv

Answer 2

Subcutaneous, Intramuscular, Intravenous

Question 3

What is unique about iv admission?

Answer 3

No absorption required, precise amount of drug enters blood

Question 4

2 drug features affecting absorption

Answer 4

1) Aq solubility (drug must be in solution)

2) Lipid solubility (to cross membrane)

Question 5

pH changes from stomach to duodenum to small intestine

Answer 5

1-3, 5, 5-7

Question 6

Bioavailbility

Answer 6

Proportion of active drug appearing in the plasma after administration. 100% for IV administration.

Question 7

Which is faster, distribution or elimination?

Answer 7

Distribution

Question 8

Volume of distribution and the formula

Answer 8

Volume of body water in which a drug APPEARS to be dissolved in after it has distributed throughout the body. It is the APPARENT VOLUME.

it tells you how much drug will give a particular concentration of drug in plasma.

Vd = X/C

Question 9

Factors determining volume of distribution (2)

Answer 9

1) Drug binds to plasma proteins (greater concentration appears in plasma, Vd is small as C is bigger)
2) Drug binds to tissues/taken up by cells (Drug is stripped from plasma, Vd is large as C is smaller)

Question 10

Can Vd be larger than total body water?

Answer 10

Yes

Question 11

Acidic drugs are ___ in high basic pH and is less lipid soluble in ___ pH

Answer 11

charged, high

charged = not lipid soluble

e.g. Aspirin is charged at high pH and not lipid soluble, hence excreted.

Question 12

Are basic drugs absorbed from stomach?

Answer 12

No, absorbed entirely at small intestine.

Question 13

Probenecid is used to treat gout. Why is it banned in sport?

Answer 13

It competes with other drugs for tubular secretion, hence reducing renal excretion of acidic drugs (masks appearance of other banned substances in urine)

Question 14

Globular filtration and tubular secretion, which one can remove protein-bound drugs?

Answer 14

Tubular secretion

Question 15

How is aspirin overdose treated?

Answer 15

Administer NaHCO3 to make urine basic and hence increase amount of ionised aspirin which won’t be lipid soluble and hence reduced reabsorption and increased excretion.

Question 16

Equation for renal clearance

Answer 16

CLrenal = GF +TS - TR (ml/min)

Question 17

Renal clearance

Answer 17

Volume of plasma from which a drug is completely removed by the kidneys per unit time

Question 18

Where does drug metabolism aka biotransformation occur?

Answer 18

Liver

Question 19

Phase 1 metabolism

Phase 2 metabolism

Answer 19

1) Creates chemical functional group on drug
2) Conjugation of water soluble molecule to function group on drug (e.g. glucuronidation, sulphation, acetylation, glutathione conjugation)

These phases of metabolism make it hard for the water soluble drug metabolites to be reabsorbed and hence excreted.

Question 20

Cytochrome P450

Answer 20

Superfamily of enzymes responsible for many phase 1 drug metabolism reactions (oxidations). Action can be inhibited or enhanced by drugs.