Sorry to hear of the allergic reaction from Letrozole JMC (Letrozole is a generic form of the original medication and is made by many manufacturers under different names.)
A rash is one of the possible side effects, sadly. Here is ONE confirmed case & how it was treated (maybe send the link to your GP?):
https://pmc.ncbi.nlm.nih.gov/articles/PMC4129361/
Letrozole is available under its original brand name Femara as well as many generic manufacturer labels and brands, but may cost more.
Common Generic Brands and Suppliers:
ARX-Letrozole
Femolet
Gynotril
Letrozole GH / Letrozole generichealth
Letrozole Sandoz
Pharmacor Letrozole
APO-Letrozole (Apotex)
Letrozole AN
Letrozole Actavis
Teva Pharms - are all generic formulations of Femara
Sometimes it can actually be the COATING on the tablet that may cause a problem.
The actual medical ingredients are the same as the 'original' brands (Femara, made by Novartis, is the original medicine with Letrozole as the active ingredient)... but the coating (designed to break down after a specific time in the stomach) 'may' be made of different ingredients to the 'parent' medicine.
I hope the cortisone cream works for you to control it xx