Adrenaline before snakebite anti-venom reduces allergic reactions - Lankan Study

Treating snakebite victims with a low dose of adrenaline before the antivenom can reduce the risks of severe allergic reactions, according to a new Sri Lankan study. The study also shows that two other commonly used premedications can be doing more harm than good.

 

In some countries where snake bites are a major health problem, acute allergic reactions to poor quality antivenoms are common and often fatal.

 

The study, led by Dr Asita De Silva of the Faculty of Medicine at University of Kelaniya, Sri Lanka, demonstrates that two common premedications, the antihistamine promethazine and the corticosteroid hydrocortisone, have no value and may even be harmful.

 

The research, published today in PLoS Medicine, centres on a study of more than 1000 people who were hospitalised in Sri Lanka for snakebite.

 

In the study, the authors randomised patients to receive low-dose adrenaline, promethazine, hydrocortisone or a placebo — alone and in all possible combinations — immediately before treatment with an antivenom infusion. Compared with the placebo, pretreatment with adrenaline reduced severe reactions to the antivenom by 43 per cent at one hour and by 38 per cent over 48 hours.

 

Neither hydrocortisone nor promethazine given alone reduced the rate of adverse reactions to the antivenom. Giving adrenalin in conjunction with hydrocortisone appeared to negate the beneficial effect of adrenaline.

 

The findings also emphasise the high rate of acute adverse reactions to antivenom and stress the importance of improving the quality of the available antivenoms in Sri Lanka and South Asia.

 

Reaction rate in Sri Lanka high

 

Dr Geoffrey Isbister, a snakebite and antivenom expert from the University of Newcastle in Australia was involved in the review process of the research.

 

He says antivenom in Sri Lanka is poor quality, which results in high adverse reaction rates.

 

Most snake antivenoms are made from horse blood, and the human immune system can react badly to some of the antibodies contained in it.

 

“In Australia our reaction rate is lowish, about one in 20 people have a severe reaction and one in four or five have some sort of a reaction, mild to moderate,” Isbister says.

 

He says in Sri Lanka 80 or 90 percent of patients have a reaction, and 40 to 50 percent are severe reactions.

 

According to Isbister it is common practice in Sri Lanka to give premedications before administing antivenom, often several at a time.

 

“What the study showed was that if you added hydrocortisone to adrenaline you actually not only negated the effect of the adrenaline, but potentially increased the rate of the reactions.”

 

Isbister says the study has delivered some important results, but more work is needed.

 

“I think it’s almost a definitive answer, but I think you need at least two good studies like this,” he says. “This is enough to say that you should only be using adrenalin as a premedication, there’s no justification to give promethazine or hydrocortisone.”

 

Isbister says premedication with adrenalin used to be common practice in Australia, but that as most snakebites these days are treated in well-equipped emergency rooms, the practice has since been stopped.

 

“In Australia we would say that you’re better off being treated if you have a reaction, than being treated prophylactically.” ABC reports.