Pharmacokinetics: metabolism

Question 1

What are the phase I reactions

Answer 1

oxidation, reduction, hydrolysis.

Question 2

What are phase 1 reactions performed by

Answer 2

P450 enzymes but some drugs are metabolised by specific enzymes, for example alcohol dehydrogenase and xanthine oxidase. Products of phase I reactions are typically more active and potentially toxic

Question 3

What are the phase II reactions

Answer 3

conjugation

Question 4

How are phase II products excreted

Answer 4

Products are typically inactive and excreted in urine or bile. Glucuronyl, acetyl, methyl, sulphate and other groups are typically involved

Question 5

What is first pass metabolism

Answer 5

This is a phenomenon where the 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 6

What drugs are metabolised by the liver

Answer 6

aspirin
isosorbide dinitrate
glyceryl trinitrate
lignocaine
propranolol
verapamil
isoprenaline
testosterone
hydrocortisone

Question 7

Zero order drugs

Answer 7

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

Question 8

Drugs affected by hepatic N-acetyltransferase

Answer 8

isoniazid
procainamide
hydralazine
dapsone
sulfasalazine