Giving low-dose adrenaline to patients who have been bitten by a poisonous snake before treatment with the appropriate antivenom is safe and reduces the risk of acute severe reactions to the treatment, but giving promethazine has no such effect and giving hydrocortisone may actually be harmful. These findings from a study led by Asita De Silva from the Clinical Trials Unit, Faculty of Medicine, University of Kelaniya in Ragama, Sri Lanka, are important because in some countries where snake bites are a major health problem, acute allergic reactions to poor quality antivenoms are common and often fatal.
In a study involving more than 1000 people who were admitted to five hospitals in Sri Lanka after experiencing a snakebite, the authors randomized patients to receive low-dose adrenaline, promethazine, hydrocortisone or placebo alone and in all possible combinations immediately before treatment with an antivenom infusion. Compared with placebo, pretreatment with adrenaline reduced severe reactions to the antivenom by 43% at one hour and by 38% over 48 hours. By contrast, neither hydrocortisone nor promethazine given alone reduced the rate of adverse reactions to the antivenom and adding hydrocortisone appeared to negate the beneficial effect of adrenaline. These findings also emphasize 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.
They continue: "Until these overdue improvements come about, we have shown that pretreatment with low-dose adrenaline is an effective and safe therapy to prevent acute reactions to antivenom... Meanwhile, we continue to reiterate that the need for careful observation of patients receiving antivenom and prompt treatment of acute reactions when they occur remains undiminished."