I'm allergic to penicillin and took some accidentally. what should i do?

Be ready: People's reactions are usually (but not always) similar each time they take the same amount (dose) the same way (by mouth, injected, etc). You can use that as a guide to the kind of treatment you will need. If your reaction was severe, go the er, by ambulance if you have no one to drive you. Discuss with your doctor beforehand, not everyone who thinks they are allergic to penicillin actually is.

PCN Allergy: If nothing happened, then you are not allergic to that form of pcn-family. I would also call your doctor to discuss this and schedule with an allergist.