When you first start playing, you won't have the knowledge to craft Antibiotics—that will come later as you progress. For now, you're stuck tracking down Medicine Cabinets, Supply Crates, and Pill Cases.
I've had the most luck finding Antibiotics in Medicine Cabinets. You should spawn near a house or two, and if you're lucky, there's an RV parked somewhere in the woods nearby.
As you progress through the game, you'll find it's sometimes easier to craft necessary items instead of scouring the game world. Of course, so long as your skill is high enough, you can craft Antibiotics at a Campfire or Chemistry Station.
But be wary: residential homes in v1.0 tend to spawn many zombies. You'll open the front door expecting an easy loot run, only to find a small horde waiting for you!
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