is not justifiable to delay treatment by 20 or 30 minutes to read the results of hypersensitivity tests 10.
We observed that severe reactions were few and that they responded well to meticulous treatment with appropriate drugs. Deaths due to AVS anaphylaxis in Government hospitals are a rarity with the current practice. The onset of reaction could occur within the first 15 minutes of treatment with AVS. However, in the majority (87%) the reaction started within the first hour of AVS infusion. While the most common reaction was rigor (65%) and urticaria (57%), the development of cold and clammy skin was an indicator of increasing severity.
The dramatic response to treatment, irrespective of severity, as shown in Table 2, (31% had a duration of reaction 5 minutes and 71%, 30 minutes) emphasizes the effectiveness of AVS. However, as a precaution, medications needed to counter adverse reactions should always be readily available when AVS is given.
In some peripheral hospitals a common practice in envenoming is to use sub-therapeutic doses of 10 vials of AVS. The current observation of a lack of difference in the rate of reaction after treatment with 10 or 20 vials, should encourage practitioners to start a dose of 20 vials at the very first indication of envenoming. A similar result was found in a study done in Colombia 9 which showed that there was no significant difference in the incidence of early anaphylactic reactions between patients receiving two, four or six vials of antivenom in Bothrops snake bite envenoming.
In this study 11 patients who developed reaction to the first dose of AVS needed a second dose after six hours due to persisting envenoming. Of them five patients developed a mild reaction: a significant drop (55%) in the rate of adverse reaction. Similarly, those patients who were given AVS before being admitted to General Hospital, Anuradhapura had a significant reduction of reaction rate by 55%. This reduction in the rate and severity of reactions to repeated doses of AVS
administration may be attributed to a process of desensitization of the immune response.
This study was not designed to test the correlation between rate of administration of antivenom and the rate of reactions. Such studies reported from Nigeria and Thailand, 10 have shown that the incidence and severity of early reactions was the same whether antivenom was given by intravenous injection over 10 minutes or diluted and given as an intravenous infusion over 30 minutes. Based on these findings antivenom infusions should not be prolonged to reduce chance of adverse reactions as this may curtail the benefits of rapid neutralization of venom in the blood.
The present study elaborates the natural history of the reaction to AVS administration in clinical practice in Sri Lanka. Results show that adverse reactions respond well to standard practice of management of allergy and anaphylaxis. Although, hydrocortisone is believed to be a slow acting drug in anaphylaxis, we observed a rapid clearance of reaction when hydrocortisone was combined with chlopheniramine. Furthermore it is recommended that adrenaline should always be available in the emergency tray.
Even though, reactions to AVS treatment is common,
the response to treatment for reaction is effective.. Intravenous
hydrocortisone 400mg plus chlopheniramine 10mg should be administered
promptly with the onset of reaction. As the reaction rate was not
dose dependent and AVS therapy is effective, patients should be given
full dose of AVS (10 to 20 vials depending on the severity of systemic
envenoming) when indicated. Furthermore, importance of atopic history
of the patient is questionable as a predictor of sensitivity reactions
to AVS. An emergency tray with effective medications for treating
anaphylaxis should be available before embarking on AVS therapy.