Effectiveness of Zagreb antivenom against envenoming by the adder, Vipera berus.

Rhesus monkeys injected subcutaneously with 2, 3, or 4 mg Vipera berus venom per kg body-weight all died in shock. With 1 mg/kg the monkey had severe systemic and local effects taking 12 days to resolve. Five monkeys each recieved 4 mg/kg (a triple-lethal dose) and Zagreb antivenom was injected intravenously 1-4 hours after venom injection. The contents of 2 ampoules (10-8 ml) up to 3 hours later saved the monkeys; at 4 hours later the monkey died. But when the antivenom dose was raised to 16-2 ml 4 hours after venom, it saved the monkey. In addition to saving life, the antivenom greatly reduced the local venom effects. It is suggested that the results justify giving Zagreb antivenom to patients with severe adder-bite poisoning; and it should also be considered in adults to minimise morbidity from local effects.