Well, I'm quitting Firered Nuzlock.
I've tried about 10 times [Counting the attempts I made in the past, way back], and each time, get put in a position where I won't be able to proceed further, be it Bulbasaur getting critted early on, leaving you with no pokemon to take on the Poision-types, or Brock, or the rest of my team getting posioned by the literal army of Poision types you fight, leaving nothing but Poision types in your possession, causing your defeat when you get to Sabrina.
Stupid Poision...
If you're worried about poison in Fire Red so much (which is a reasonably-founded fear), then fight off Poison-types with your own. It's a really good idea to fight Koga with your army of Poison-types (and a Snorlax with Immunity if you have one) so that you might have monsters to spare when you encounter Sabrina.
I've been doing a Nuzlocke run on Fire Red lately, and poison types are fantastic here. Zubats are a bit of a pain to level up, but once it knows Bite and Wing Attack, it's gonna be a massive help against both Erika and Koga.
I'm not sure why Erika is such a big deal; go in there with like two or three flyers with Wing Attack/Aerial Ace/Fly, and you can decimate the gym in no time. And if you do get poisoned (kind of unlikely), just Fly back to the Center (provided you have more than 1 HP left).
As for Koga, it is scary to fight the two Koffing that Selfdestruct, but if you can beat them or make their Selfdestruct miss somehow, it's not that bad. Snorlax with Immunity, as well as Poison-types with non-Poison attacks, are highly recommended here. Golbat had Bite and Wing Attack, and I should've taught my Vileplume Cut or Secret Power instead of Acid.
Then again, it's my first Nuzlocke run. Maybe I'm just lucky (or overleveling). Basically, fight poison with poison. Just a thought.