Antivenom cannot reverse the effects of venom once they've begun, but it can prevent it from getting worse. In other words, antivenom cannot un-block a channel once it's already been blocked. Over time, your body will repair the damage caused by the venom, but antivenom can make it a much smaller repair job.

Why can you only get anti venom once?

Is it true that you can only get antivenom once? ... The reason was that a person's immune system might recognize the animal serum in the antivenom, and there might be either a serious allergic reaction or a severe case of “serum sickness.” But even back then, many people got antivenom a second (or third, or fourth…)

How long does anti venom last?

For best results, antivenom should be given as soon as possible after the bite. It is usually given within the first 4 hours after the snakebite and may be effective for 2 weeks or more after the bite.