The polyvalent antivenin is produced by injecting horses with adapted venom. This gives the antivenin its polyvalent property. While not type-specific, the polyvalent antivenin CroFab is generally used to treat serious envenomations. There is no antivenin specifically manufactured for copperheads. The antivenin can cause an immune reaction called serum sickness. No antivenin is available for bites from either subspecies. Wyeth discontinued the manufacture of coral snake antivenin in 2010, citing a lack of profitability. The fresh nuts are believed to be a snake antivenin. Currently, there is no antivenin that provides protection against bites from this species. The previous antivenin (ACP) is no longer manufactured. This also enhances the potency of the antivenin. In all cases, specific antivenin was used and there were no deaths. Antivenin is produced by the Instituto Nacional de Higiene in Mexico. The antivenin CroFab, while not type-specific, can be used to treat severe envenomations from massasaugas. Most patients remained stable and did not require antivenin.