Interventions for preventing reactions to snake antivenom

People die or can be seriously disabled after being bitten by a venomous snake. Different venomous snake species have different effects on the body, but initial treatment is similar - to try and prevent venom entering the general circulation. If it becomes apparent that the venom has reached the bloodstream, the patients start becoming extremely unwell and in these circumstances health staff may give a specific antivenom (made from horse serum). However, antivenom frequently causes adverse effects which can, in themselves, be severe and result in death.

There are drugs that can be given with the antivenom to try to reduce these adverse effects, and these include adrenaline, antihistamines, and steroids. The review looked to assess the benefit of giving these drugs along with the antivenom. The review of trials found one trial of 105 people in Sri Lanka looking at adrenaline; and a second trial of 101 people in Brazil looking at an antihistamine (promethazine). Both trials were well designed. Adrenaline showed fewer allergic reactions. There was no benefit seen from giving promethazine, and no trials were found on late allergic responses, nor on corticosteroids.

Authors' conclusions: 

Routine prophylactic adrenaline for polyvalent antivenom known to have high adverse event rates seems sensible, based on this one trial. If clinicians believe local factors do not justify routine adrenaline, then they should test their belief in a randomized trial. Antihistamine appears to be of no obvious benefit in preventing acute reactions from antivenoms.

Read the full abstract...
Background: 

Antivenom is used to neutralise snake bite toxins in people showing evidence of envenomation. It is made from animal sera, and adverse effects, including life threatening anaphylaxis, are common.

Objectives: 

To assess the effects of drugs given routinely with snake antivenom to prevent adverse effects.

Search strategy: 

Cochrane controlled trials register; contact with researchers in the field.

Selection criteria: 

Randomized and quasi-randomized trials testing routine adrenaline (epinephrine), antihistamines, or corticosteroids.

Data collection and analysis: 

The two authors applied the inclusion criteria, assessed trial quality, and extracted the data. We sought additional data from trialists where required.

Main results: 

One trial in Sri Lanka (n = 105) giving adrenaline with polyspecific antivenom showed fewer adverse reactions in the adrenaline group, and this effect was preserved when stratified for severity. One trial in Brazil (n = 101) using three types of Bothrops antivenom showed no benefit of antihistamine drugs.

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