Sublingual glyceryl trinitrate as prehospital treatment for hypertension in Irukandji syndrome

To the Editor: Fenner and Lewin describe three cases of Irukandji syndrome in which glyceryl trinitrate (GTN) was used to transiently lower blood pressure.1 However, they provide no evidence that this relieved the patients’ pain or improved their ultimate outcome (development of pulmonary oedema or myocardial injury); they therefore do not show sufficient evidence for instituting such therapy. It is worrying that, with little evidence, sublingual GTN is now recommended as a prehospital treatment in Irukandji syndrome. Although GTN has been used safely in other conditions, its use without adverse effects in three patients is not evidence that it can be used safely in treating jellyfish envenoming.

It is of concern that the treatment of bites and stings remains based on anecdotal evidence, and that clinical toxinology has not moved with the rest of medicine to developing evidence-based approaches. Fenner and Lewin state, in their second paragraph, that intravenous magnesium has proven to be effective in treating symptoms of Irukandji syndrome. This is based on a single case report and no controlled trials. It simply provides a starting point so that properly designed studies can be done to determine if magnesium is effective and safe in Irukandji syndrome. It is not appropriate to suggest that magnesium is a proven therapy without further investigation.

Are we not learning from previous problems in clinical toxinology and prehospital care? Both are areas of medicine where treatment protocols are rarely based on substantial evidence.2,3 The pressure immobilisation bandage was introduced for the first-aid treatment of Chironex fleckeri stings with no supporting evidence, and it has taken two well designed animal studies to show that this is dangerous.4,5 A recent well designed study in the United States showed that prehospital intubation by paramedics of patients with head injury resulted in transient desaturation in 57% of patients and significant bradycardia (< 50 bpm) in 19%.6 This occurred despite the paramedics describing the intubation as “easy” in 84% of the patients who desaturated. This shows that it is essential to properly evaluate the safety and efficacy of treatments before recommending them for prehospital use.

Although the infrequency of many envenoming syndromes makes controlled studies difficult to do, it is essential that clinical investigators collaborate to institute such studies. This is now happening in Australia with the commencement of randomised controlled trials on redback spider antivenom, magnesium in Irukandji syndrome and hot-water first-aid in jellyfish stings. Hopefully we will move from anecdote to evidence in clinical toxinology with collaborative studies such as these.