Current use of Australian snake antivenoms and frequency of immediate-type hypersensitivity reactions and anaphylaxis

Abstract

Objective: To investigate current use of Australian snake antivenoms and the frequency and severity of immediate-type hypersensitivity reactions.

Design: Nested prospective cohort study as part of the Australian Snakebite Project.

Patients and setting: Patients receiving snake antivenom in Australian hospitals between 1 January 2002 and 30 November 2007.

Main outcome measures: The use of CSL Limited antivenom; frequency and severity of hypersensitivity reactions to antivenom; premedication and treatment of these reactions.

Results: Snake antivenom was administered to 195 patients, mostly for venom-induced consumption coagulopathy (145 patients, 74%), followed by non-specific systemic effects (12%), neurotoxicity (5%) and myotoxicity (4%). Antivenom was given to nine patients (5%) without evidence of envenoming or who were bitten by a species of snake for which antivenom is not required. The commonest antivenoms used were brown snake (46%), tiger snake (30%) and polyvalent (11%). The median dose was four vials (interquartile range, 2-5 vials), and 24 patients received two different types of antivenom. Immediate-type hypersensitivity reactions occurred in 48 patients (25%); 21 satisfied our definition of anaphylaxis, with 11 moderate and 10 severe cases, including nine in which patients were hypotensive. The remaining 27 reactions were mild (skin only). Adrenaline was used in 26 cases with good effect. The frequency of reactions to tiger snake (41%) and polyvalent (41%) antivenoms was higher than that to brown snake antivenom (10%). Hypersensitivity reactions occurred in 11 of 40 patients receiving any form of premedication (28%) and in 2 of 11 given adrenaline for premedication (18%) versus 20 of 86 not receiving premedication (23%).

Conclusions: Antivenom was used appropriately, and most commonly for coagulopathy. Hypersensitivity reactions were common, but most were not severe. The discretionary use of premedication was not associated with any reduction in reactions.