The fact that chemo papain is was given to patients without testing for allergies is typical of doctors. Allergy has been testing has been around for close to 100 years. Doctors also use contrast dyes without knowing if patients are allergic. It is probably more lucrative to make money treating 2 or 3 percent patients for the dangerous reactions than testing them.
Alcohol is not much of an allergen and often it requires more than one injection so it probably dissolves tissue very slowly and then stops.
Here's a video about discogel
DiscoGel and Water - YouTube
Here is a patient getting an injection with English titles
C5 C6 English - YouTube
Fixmybackdisc.com - Discogel Injection - YouTube