Ability of a polyvalent antivenom to neutralize the venom of Lachesis muta melanocephala, a new Costa Rican subspecies of the bushmaster.

Several toxic and enzymatic activities of the venom of L. m. melanocephala were studied. This venom has many similarities with that of L. m. stenophrys, although there are quantitative differences in venom activities, as well as in the immunodiffusion patterns of these venoms when reacted against polyvalent antivenom. This antivenom was tested for its ability to neutralize a series of toxic and enzymatic effects of L. m. melanocephala venom. A new method to study myonecrosis, based on the quantitation of residual creatine kinase in injected muscle, was used. Antivenom was highly effective in neutralizing lethal, hemorrhagic, myotoxic, edema-forming, defibrinating, caseinolytic and fibrinolytic activities when venom and antivenom were incubated prior to the test or, in the case of edema-forming activity, when antivenom was administered before venom injection. On the other hand, when antivenom was injected i.v. at different time intervals after venom injection neutralization of lethality was good, although neutralization of local effects, i.e. hemorrhage and edema, was poor. These results indicate that polyvalent antivenom contains antibodies capable of neutralizing toxic and enzymatic activities of L. m. melanocephala venom. Moreover, the partial inability of antivenom to neutralize local effects when administered after venom injection is probably due to the rapid development of these effects once venom is injected.