Equirab Equirab contains equine rabies immunoglobulin, consisting of specific antibodies obtained from the plasma of horses immunized against rabies virus. It works by providing immediate passive immunity through neutralizing circulating rabies virus particles at the wound site, preventing virus attachment and entry into nerve endings until active immunity is produced by rabies vaccine. It is indicated for post-exposure prophylaxis against rabies in Category III exposures (single or multiple transdermal bites or scratches, contamination of mucous membrane with saliva from animal).