Should dogs bitten by European adders be given antivenom?

23 January 2018, at 1:44pm

"In dogs with a European adder bite, does the use of antivenom with supportive treatment compared to supportive treatment alone improve time to recovery?" published in Veterinary Evidence in November, discovered no available studies directly comparing treatment with or without antiserum, meaning it remains uncertain whether it is genuinely effective in dogs.

Among the evidence, which amounted to three studies between 2011 and 2015, no significant difference in mortality rate was found between dogs treated or not treated with antiserum. Although one study did report a faster improvement to local swelling around the site of envenomation, this finding was contradicted elsewhere. As such, there is no clear evidence base to recommend the use of antivenom in practice.

However, this doesn’t mean that antiserum should not be used to treat a dog likely to have been bitten by a European adder – also known as the common adder or European viper – particularly if clinical signs are severe.

Does weak evidence mean antivenom does not work?

Even though the available evidence is low quality and has limitations, there was a suggestion that the administration of antivenom within 24 hours of being bitten improved the mental status of dogs. Furthermore, dogs treated with antiserum had lower concentrations of proteins in their urine two weeks after treatment.

But despite this potential efficacy, the fact that the vast majority of dogs recover from adder bites – combined with an antiserum adverse reaction rate similar to that of humans – means that antivenom is unlikely to be necessary in most cases. The practitioner should judge whether clinical signs are severe enough to warrant treatment with antivenom rather than just supportive treatment such as antihistamines.

Sourcing issues

There is currently no licensed antiserum for the treatment of adder envenomation in dogs (or any other animals) in the UK, so the human product has to be imported from elsewhere. It is recommended that practices obtain a Special Treatment Certificate from the Veterinary Medicines Directorate and keep an emergency stock of antivenom.

Getting hold of an immediate source of European adder antiserum is very difficult but there are 16 clinics across the country that stock it as part of the ToxBox 24-Hour Service, a joint venture between Vets Now and the Veterinary Poisons Information Service (VPIS).

If you are faced with a dog in emergency need of antivenom, call VPIS on 020 7188 0200.

Full Knowledge Summary: Authors: Lindsay Hodgson and Giorgia Brambilla