The anti-Venom gas was created by Donatello in Batman/Teenage Mutant Ninja Turtles II.
At Bane's demand, Baxter Stockman synthesized a new form of Venom that was more potent than the type from Bane's own universe. However, Donatello later isolated a critical flaw in the chemistry of the Venom, which meant that it could be easily and quickly flushed from the body.
Donatello quickly created a gas to purge Venom from the body, and tested it on himself. It worked almost immediately, reducing him to his former size and strength. Later, he bombed the entirety of Liberty Island with the gas, purging the Venom from Bebop, Rocksteady and the numerous Foot ninja who had been dosed with it.
It did not have an effect on Bane. It is unclear whether this was due to his many years of using Venom, or because he was at a greater altitude than the other users of the drug.