Abstract:
Russell's viper (Daboia russelii russelii) is an important cause of
morbidity and mortality in Sri Lanka. In a study in 1985, Haffkine equine
polyspecific antivenom in doses up to 20 g proved ineffective in clearing
antigenaemia and caused a high incidence of anaphylactoid reactions. A new,
monospecific ovine Fabantivenom (Polonga TAb) has been developed against the
venom of Sri Lankan Russell's viper and, to assess its safety and efficacy, we
carried out (in 1997) an open, randomized comparison of this with the Haffkine
antivenom currently in use in the country. Patients with systemic envenoming
following Russell's viperbite were randomized to receive an initial intravenous
dose of either 1 g of Polonga TAb (n = 23) or 10 g of Haffkine antivenom (n =
20). One dose of Polonga TAb permanently restored blood coagulability in only 9
(41%) of 22 patients and 13 needed repeated doses, whereas the majority (14/20;
70%) had restored coagulability after 1 dose of Haffkine antivenom. There was a
tendency towards more rapid resolution of local swelling and systemic
manifestations in the Haffkine group. Venom antigenaemia was eliminated more
quickly in the Haffkine group and ovine Fab was cleared from the circulation
more rapidly than equine F(ab')2. To evaluate safety, patients were closely
observed for adverse reactions. Following a severe reaction with Haffkine
antivenom all subsequent patients in this group were treated prophylactically with
hydrocortisone and chlorpheniramine. Despite this, the incidence of adverse
reactions was significantly higher in the Haffkine group compared with the
PolongaTAb group (81% compared with 48%) and 4 patients had a severe
anaphylactic reaction in the former group. In conclusion, the new antivenom is
safer than Haffkine antivenom but, to avoid repeated doses, an initial dose higher
than 1 g is needed in thetreatment of Sri Lankan Russell's viper envenoming. The
safety of this larger dose is the subject of further studies.
