Question 5

College Answer

Balance between potential severity of poisoning, time from ingestion and risk to the patient of interventions considered.  Most overdoses do not develop significant toxicity but reasonable to use technique with low morbidity and reasonable efficacy in all except clearly non-toxic ingestions (eg. single dose activated charcoal [1g/kg]).  Induced emesis with ipecac induces risks without evidence of decreased absorption.   Gastric lavage is associated with reasonable decrease in absorption if performed  early (e.g. < 1 hour), though it is associated  with increased  risks (including  visceralinjury and aspiration); it may have additional benefit if combined with activated charcoal.  Repeat doses of charcoal are usually not of additional benefit except perhaps where a large amount of toxic substance adsorbed by charcoal was ingested (especially slow release preparations).   Whole bowel irrigation (using polyethylene glycol e.g. golytely) may have specific benefit with slow release preparations or agents that are poorly absorbed by activated charcoal.  Rarely endoscopy or surgical removal is indicated. 

Discussion

This question closely resembles section (b) from Question 1 of the second paper of 2004. However, here it is presented on its own, as a 10-mark question, and so some extra thought should be spent on it.

In brief, decontamination can be critically evaluated in the following manner:

Rationale for decontamination

• In any overdose, especially early, there is some proportion of the ingested drug which still has not absorbed.
• This unabsorbed drug could potentially be cleared from the gut
• This would result in a reduced total dose of the drug
• The reduced total dose should also result in a reduced total toxicity
• Ergo, the removal of undissolved drugs should reduce the toxicity of the overdose

Techniques of decontamination and their indications

• Activated charcoal, single or multiple doses
• Induced emesis (abandoned)
• Gastric lavage (largely abandoned; only indicated within the first hour)
• Whole bowel irrigation (only indicated for iron and slow release enteric coated tablets)
• Surface decontamination for skin-absorbed toxins

Situations which merit the use of gut decontamination

• The overdose is recent (within the last hour)
• There is reason to believe a large number of undissolved tablets is still present in the stomach or gut
• There is no adequate antidote to the drug, and the overdose is lifethreatening

Criticsm of gut decontamination techniques

• Possibility of aspiration is ever-present, particularly if the airway is unprotected
• Likelihood of effect diminishes with time.
• Even charcoal may have serious complications, eg. bowel obstruction
• Many of the early studies which lauded the effectiveness of gut decontamination techniques such as emesis or lavage were focused on the effectiveness of the emetic in achieving emesis, or in the lavage recovery of some abstract marker substance. No studies focused on patient outcome. Patient outcomes do not seem affected by decontamination techniques.
• The removal of a proportion of ingested drug may have no effect on the course of the overdose, in terms of outcome. One may think of this in terms of the difference between absorbing 100g of paracetamol vs. only absorbing 75g. In either case, your liver is screwed.

The website of the American Academ of Clinical Toxicology has several position statements which might be useful to the fellowship candidate:

Ipecac Syrup

Single-Dose Activated Charcoal

Multi-Dose Activated Charcoal

Cathartics

Whole Bowel Irrigation

Gastric Lavage

Urine Alkalization

Gaudreault, Pierre. "Activated charcoal revisited." Clinical Pediatric Emergency Medicine 6.2 (2005): 76-80.

Andersen, A. Harrestrup. "Experimental Studies on the Pharmacology of Activated Charcoal. III. Adsorption from Gastro‐Intestinal Contents." Acta Pharmacologica et Toxicologica 4.3‐4 (1948): 275-284.

Krenzelok, Edward P. "New developments in the therapy of intoxications." Toxicology letters 127.1 (2002): 299-305.

Eddleston, Michael, et al. "Multiple-dose activated charcoal in acute self-poisoning: a randomised controlled trial." The Lancet 371.9612 (2008): 579-587.

Isbister, Geoffrey K., and Venkata V. Pavan Kumar. "Indications for single-dose activated charcoal administration in acute overdose." Current opinion in critical care 17.4 (2011): 351-357.

Chyka, P. A., and D. Seger. "Position statement: single-dose activated charcoal. American Academy of Clinical Toxicology; European Association of Poisons Centres and Clinical Toxicologists." Journal of toxicology. Clinical toxicology 35.7 (1996): 721-741.

Daly, F. F. S., M. Little, and L. Murray. "A risk assessment based approach to the management of acute poisoning." Emergency medicine journal 23.5 (2006): 396-399.

Olmedo, Ruben, et al. "Is surgical decontamination definitive treatment of “body-packers”?." The American journal of emergency medicine 19.7 (2001): 593-596.