A new monospecific ovine Fab fragment antivenom for treatment of envenoming by the Sri Lankan Russell's viper (Daboia Russelii Russelii): a preliminary dose-finding and pharmacokinetic study.

Abstract

Abstract. Russell's viper is the most important cause of life-threatening snake bite and acute renal failure in Sri Lanka. Only equine polyspecific antivenoms imported from India are available. They have not proved effective clinically or in clearing venom antigenemia and they frequently cause reactions. In an attempt to reduce mortality and morbidity, a new monospecific ovine Fab fragment antivenom (PolongaTab ; Therapeutic Antibodies, Inc., London, United Kingdom) was raised against Sri Lankan Russell's viper venom. In a preliminary dose-finding study in 35 patients, an initial dose of 3-4 g restored blood coagulability permanently and stopped systemic bleeding, even in severely envenomed patients. Venom antigenemia disappeared within 1 hr of antivenom treatment but recurred, probably as a result of continued absorption of venom from the site of the bite, after the rapid clearance of therapeutic antibody. Twelve patients (34%) experienced early reactions that were usually mild and always responded to epinephrine.

Detection of venom after antivenom administration is largely due to bound venom

“…For this to be true, there would be simultaneous detection of recurrent venom and clinical and/or laboratory evidence of envenoming. However, the vast majority of reports are of recurrent venom detection (antigenaemia) without recurrent envenoming (Ariaratnam et al, 1999;Ho et al, 1986;Phillips et al, 1988;Theakston, 1997). This is demonstrated in the study by Otero et al where they found recurrence of venom in serum samples in eight of 52 patients, 6e72 h post-antivenom, but no evidence of recurrent coagulopathy.…”

Snakebite Envenoming: A Public Health Perspective

“…On the other hand, low molecular mass Fab fragments have a relatively short half-life, thus resulting in the phenomenon of recurrence of envenoming, i.e. the reappearance of signs and symptoms of envenoming several hours after antivenom therapy (Ariaratnam et al, 1999;Boyer et al, 2001;Meyer et al, 1997). Careful clinical following up of patients is necessary to determine the need of an additional dose of antivenom.…”

Snake antivenoms: adverse reactions and production technology

“…For patients known to be sensitive to equine proteins, avoidance of antivenoms prepared in this manner is mandatory and should reduce the incidence of anaphylactic shocks. Some production laboratories are now successfully using other animals like sheep as sources of sera (7,28,39). Recent studies indicate the use of camels for antivenom production, due to lower in vitro complement activation than found in horses and sheep (40,41).…”