From what i read, before the anti-venom can act against the venom in the bloodstream, some of the venom has been absorbed into the organs. Then the affected animal is seemingly stable. Then it depends on how badly the organs, like the liver and kidneys, were initially impacted. So they keep checking urine output etc. So basically the anti-venom diminishes the dose of venom received, but its not like an antibiotic where it "kills venom cooties."