Sakura makes three doses: one for Kankuro, and two for the upcoming battle, anticipating they will face the same poison again.
The "Large Scale Oil/Water extraction" method Sakura uses is a fantasy version of real-world dialysis or toxicology flushing. Naruto Shippuuden (Dub) Episode 11
Compare the changes from the original Japanese. Sakura makes three doses: one for Kankuro, and