The Serum is found in both Resident Evil Remake and Resident Evil Code: Veronica.
Remake
The serum is found in a security room. The player needs to get for Rebecca to save Richard, which was attacked and poisoned by Yawn. If the player is attacked when fighting against Yawn for the first time, the serum will be necessary again.
Code: Veronica
The serum is found a room at Antarctic Research Facility. This serum was created for poison too, but it was specially for Nosferatu's poison, which cannot be cured by Blue Herbs. Chris will only get it, if Claire was attacked by Nosferatu.
Others
There is also the serum used by Dr. Cameron when she was infected by the T-Virus. The serum cured her, but it also had some mixed effects.