For copperhead, rattlesnakes, and cottonmouth bites we use Crofab antivenom which is the only one that is FDA approved for use in the USA. When and how much is based on the severity of symptoms. All cause tissue damage. Rattlesnakes also cause problems with the blood thinning so their bites tend to be worse. Antibiotics are usually not needed as most bites don't get infected. Crofab is not used on coral snake bites as their venom is a neurotoxin. All of the USA made antivenom has expired and the Mexico made is not approved for use in the USA. Treatment is pretty much symptomatic. If you quit breathing you get intubated and put on a ventilator. It's a myth that coral snakes do not have fangs and have to chew to inject venom. Coral snakes do have fangs, they are just smaller than the pit vipers. They can bite and a scrape from a fang will cause envenomation. This link is to the Miami-Dade Venom One unit list of antivenoms and what species they cover. Crofab is made using sheep instead of horses. There is very little incidence of allergic reaction like there was with the old horse serum.
http://www.miamidade.gov/fire/library/antivenom-species-covered.pdf
