Pharmacokinetics: metabolism

Question 1

what are phase 1 reactions ?

Answer 1

oxidation, reduction, hydrolysis

Question 2

phase 1 reactions are performed by ?

Answer 2

P450 enzymes

some drugs are metabolised by specific enzymes eg alcohol dehydrogenase and xanthine oxidase

Question 3

Products of phase I reactions are typically

Answer 3

active and potentially toxic

Question 4

what are phase 2 reactions ?

Answer 4

conjugation - Glucuronyl, acetyl, methyl, sulphate and other groups are typically involved

Question 5

Products of phase 2 reactions are typically

Answer 5

inactive and excreted in urine or bile
lipid soluble

Question 6

what is first pass metabolism?

Answer 6

concentration of a drug is greatly reduced before it reaches the systemic circulation due to hepatic metabolism. As a consequence much larger doses are need orally than if given by other routes

Question 7

which drug goes through first pass metabolism ?

Answer 7

aspirin
isosorbide dinitrate
glyceryl trinitrate
lignocaine
propranolol
verapamil
isoprenaline
testosterone
hydrocortisone

Question 8

what is Zero-order kinetics

Answer 8

metabolism which is independent of the concentration of the reactant - undergo constant elimination regardless of the plasma concentration

Question 9

cause of what is Zero-order kinetics?

Answer 9

due to metabolic pathways becoming saturated resulting in a constant amount of drug being eliminated per unit time.

Question 10

drugs with zero order kinetics ?

Answer 10

phenytoin
salicylates (e.g. high-dose aspirin)
heparin
ethanol

Question 11

50% of the UK population are deficient in which enzyme

Answer 11

hepatic N-acetyltransferase

Question 12

drugs affected by hepatic N-acetyltransferase / acetylator status

Answer 12

isoniazid
procainamide
hydralazine
dapsone
sulfasalazine