Cross-Reactivity against Naja sumatrana (Black Spitting Cobra) Envenoming from the Haffkine Antivenom in a Mouse Model

Naja sumatrana is the dominant cobra species in Malaysia, Singapore, Borneo, and Sumatra, and it does not have specific antivenom. The Haffkine antivenom has been advocated instead. This study aims to determine the efficacy of this antivenom against Naja sumatrana envenoming using a mouse model. Methods. Male Swiss albino mice were used. Intravenous LD(50) was first determined separately for Naja naja and Naja sumatrana venom. ED(50) was determined by preincubating antivenom with each venom at 2.5 LD(50) before administering the mixture into the tail vein. Validation was carried out using a challenge test. Each mouse received 111 µg of Naja sumatrana venom intramuscularly followed by intraperitoneal administration of dilute Haffkine antivenom. Survival was recorded 24 hours after envenoming. Results. The LD(50) of Naja naja venom was 78.13 µg, standard error (SE) 13.3 µg. The ED(50) of the Haffkine antivenom against Naja naja venom was 45.9 mg, SE 7.5 mg. The LD(50) and ED(50) of Naja sumatrana venom were 55.5 µg, SE 12.0 µg; and 73.9 mg, SE 12.0 mg, respectively. The intra-peritoneal ED(50) against 111 µg intramuscular Naja sumatrana venom was 136.95 mg, SE 36.74 mg. Conclusion. The Haffkine polyvalent antivenom exhibited cross-neutralisation against Naja sumatrana venom when used at a higher dose.