Chapter 7 Answers to self check questions

1. The restriction on the quantity of paracetamol tablets that can be sold is related to the serious consequences of paracetamol overdose even though, at normal doses, paracetamol is a very safe drug. Overdose of paracetamol can cause irreversible liver damage and is potentially fatal.

2. The liver toxicity problem with paracetamol is not due to paracetamol itself, but due to one of its metabolites. A small proportion of paracetamol (~4%) is oxidatively metabolised in the liver to a quinoneimine molecule. This is a very reactive species and could potentially cause damage to liver cells. However, if the normal doses of paracetamol are taken, this is not a problem because this reactive metabolite is deactivated by glutathione (see chapter 5 for the mechanism). Although only 4% of the reactive metabolite is produced, in an overdose situation, this will be a significant amount and may be sufficient to deplete the liver’s supply of glutathione. Any remaining reactive metabolite will then cause irreversible damage to the cells of the liver.