First clinical experiences with specific sheep Fab fragments in snake bite. Report of a multicentre study of Vipera berus envenoming

Abstract

Objectives: To evaluate the efficacy and safety of specific, ovine Fab fragments in the treatment of envenoming by the common adder, Vipera berus.

Design: Open study with historical controls.

Setting: Multicentre study involving patients (n = 30) with V. berus envenoming, treated in 18 Swedish hospitals during 1991-94.

Main outcome measures: Initial symptoms, clinical course after treatment, duration of hospital stay and adverse effects of the antivenom were evaluated. Two earlier studied patient groups, given either equine F(ab)2 antivenom (n = 30) or no antivenom (n = 16), were used as controls.

Results: Specific ovine Fab fragments influenced favourably the acute symptomatology as well as the long term clinical course. Acute symptoms such as hypotension, shock, vomiting, diarrhoea and CNS-depression resolved quickly. The incidence of extensive swelling involving the trunk and the length of hospital stay were both reduced significantly compared to nontreated patients (23 vs. 88% and 3.5 vs. 6 days). Also the incidence of anaemia was reduced (23 vs. 44%). These results were consistent with those obtained with equine F(ab')2 antivenom, but with ovine Fab there were no immediate anaphylactic reactions or serum sickness.

Conclusion: Specific Fab fragments produced from sheep immunized with V. berus venom were safe and effective in counteracting the effects of V. berus bite in humans. These results justify further studies of this new treatment for snake envenoming.