Before the creation of the epipen how were severe allergic reactions treated?

You didn’t specify treated by whom? Because if you mean treated by doctors or emergency first responders, then the answer is they were treated the same as they’re treated now, with the administration of intramuscular epinephrine. You don’t need an EpiPen to do that, you can use any old hypodermic syringe and a vial of epinephrine. In the hands of a doctor or EMS technician, there’s no appreciable difference in speed.

If you mean self-medication by the patient, there wasn’t any for the average person. But people with a history of allergies or asthma did carry medications, usually in the form of inhalers. This included stuff like anticholinergics, beta-2 agonists, and yes, lots of epinephrine inhalers too. The same drug in EpiPen was available for self-medication in a different form.

Epinephrine inhalers have been legally sold over-the-counter for decades. In the US, Primatene Mist was available OTC until 2012, when it was banned for environmental reasons – apparently the propellant in the can wasn’t ozone-safe or something. But epinephrine inhalers are widely available in lots of other countries (and about to be reintroduced in the US too, in some ozone-safe packaging).

So before the EpiPen, doctors and health personnel used epinephrine for severe allergies just like they do today. Average people could self-medicate with epinephrine with an inhaler, but probably the only ones who carried such inhalers were those with a history of allergies or asthma. An inhaler delivers medicine just as fast as IM injection, but it’s harder to control the exact dose and an epinephrine inhaler usually only has a shelf life of 3 months, versus a year for the EpiPen.

Of course, people could always manage the symptoms without medication in the regular way - keep the airway clear, use the recovery position to prevent choking, elevate the limbs to drain more blood into the heart to compensate for the vasodilation of shock, etc.

The idea of self-medicating with an easy to use intramuscular injection goes back to WW2, when self-injectors were developed for soldiers who might encounter nerve gas or other chemical weapons. The standard self-injector with a metered dose, spring loaded needle and plunger, and push button operation were all invented for the army. In the 70’s, someone got the idea of delivering epinephrine the same way, and thus the EpiPen was born.