Prevention Of Further Absorption Ofthe Poison

From the environment

When a poison has been inhaled or absorbed through the skin, the patient should be taken from

2 Telephone numbers are to be found in the British National

Formulary (BNF).

the toxic environment, the contaminated clothing removed and the skin cleansed.

From the gut

Oral adsorbents. Activated charcoal (Carbomix, Medicoal) reduces drug absorption better than syrup of ipecacuanha or gastric lavage, is easiest to administer and has fewest adverse effects. It consists of a very fine black powder prepared from vegetable matter, e.g. wood pulp, coconut shell, which is 'activated' by an oxidising gas flow at high temperature to create a network of fine (10-20-nm) pores to give it an enormous surface area in relation to weight (1000 m2/g). This binds to, and thus inactivates, a wide variety of compounds in the gut. Thus it is simpler to list the exceptions, i.e. substances that are not adsorbed by charcoal which are: iron, lithium, cyanide, strong acids and alkalis, and organic solvents and corrosive agents.

Indeed, activated charcoal comes nearest to fulfilling the long-sought notion of a 'universal antidote'.3 It should be given as soon as possible after a potentially toxic amount of a poison has been ingested, and whilst a significant amount remains yet unabsorbed (thus ideally within 1 h). To be most effective, 5-10 times as much charcoal as poison, weight for weight, is needed; in the adult an initial dose of 50-100 g is usual. If the patient is vomiting, the charcoal should be given through a nasogastric tube. Activated charcoal also accelerates elimination of poison that has been absorbed (see p. 155).

Activated charcoal, although unpalatable, appears to be relatively safe but constipation or mechanical bowel obstruction may be caused by repeated use. Aspiration of charcoal into the lungs can cause hypoxia through obstruction and arteriovenous shunting. Charcoal adsorbs and thus inactivates

3 For centuries it was supposed not only that there could be, but that there actually was, a single antidote to all poisons. This was Theriaca Andromachi, a formulation of 72 (a magical number) ingredients amongst which particular importance was attached to the flesh of a snake (viper). The antidote was devised by Andromachus whose son was physician to the Roman Emperor, Nero (AD 37-68).

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Constipation Prescription

Constipation Prescription

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