With an adder bite there is often rapidly increasing swelling and tenderness where the dog was bitten, usually on the muzzle, the head or a leg. The bite can be hard to see in the fur, and the two small marks left by the fangs are not always visible. How badly the dog is affected varies with the amount of venom, where the bite is and the dog's individual reaction, among other things.
In a Swedish study of 53 dogs bitten by adders, all had local swelling and almost three quarters were affected in their general condition. Some dogs later showed changes that could indicate effects on the heart, muscles or other organs. A dog that seems fairly bright straight after the bite may therefore still need to be monitored and examined.
Keep your dog as calm as possible and contact a vet right away if you suspect an adder bite. Do not give human medicines or any other treatment on your own initiative. At the vet, swelling, pain, circulation and general condition are assessed, among other things. Blood tests and monitoring may be needed. Treatment is adapted to how the dog is affected and can include pain relief, intravenous fluids and, in more severe cases, antivenom.
Seek emergency care if your dog becomes very lethargic, collapses, has difficulty breathing, or develops rapidly increasing swelling or other clear signs of being generally unwell.