Can any doc explain why can't you just use an epipen, (epinephrine) after having an allergic reaction/anaphylaxis, and then not go to the emergency room?

Wears off: This is a deadly allergic reaction and it is important that the causative agent be gone from you system or else a repeat attack can occur. The epi pen will reverse these effects for a time but if you aren't followed and have other agents to suppress immune function like steroids and iv fluids there is a risk that when the epi wears off the reaction returns