With the Lizard temporarily unconscious on the ground, spiderman covers him with webbing and begins to run around the lab, looking for anything he can find. He comes across multiple failed vials, and then an interesting chemical formula. It takes him a second to understand what it is before quickly looking around for the ingredients he needs.
The antidote wasn't strong enough - it was a prototype. It didn't account for the healing factor, and size of the new body. Luckily the formula was quite simple, and would only take a minute to make. Peter mixes the ingredients together into a centrifuge, and pushes the button. No luck. Peter switches the fuse on the wall, and the power churns to life in the building. He pushes the button again. 20 seconds.
The lizard isnt on the floor.
18 seconds. Spiderman closes his eyes, allowing his spider sense to envelope him.
15 seconds.
Scutling sounds.
10 seconds. Hot breath on his neck.
7 seconds.
Claws raised behind him
4 seconds.
The floor shifting slightly from his sheet weight.
1 Second.
As the lizard goes to smash Spidey and the centrifuge, he grabs it in one fluid motion and backflips over him, pouring the liquid down his open gullet.
Now he just has to survive long enough for it to take affect.