AD Teemo's Toxic shot deals same amount of damage as ap.

So just had a game with a teemo who had around 289 ad something like that with 42 ap. and his toxic shot dealth just as much as if he would build ap, when i built MR the damage got reduced, but even at 120 ap within around 5 seconds AS AD it dealth 342 damage, when i had around 60 MR it dealth 600+

This is when he stacked Attack damage, and not ap. It's supposed to do like no damage if you don't build any ap. OTherwise it explains that toxic shot just scales of its level and not the AP you stack with it.