allergic to roxicet but not percocet etc

Have taken percocet 5/325, generic oxycodone w/apap 5/325, endocet 5/325 and roxicet 5/325. The roxicet caused a severe allergic reaction within an hour of taking 1/2 a dose. I had severe difficulty breathing which fortuneatly was reversed by a dose of benadryl. I would like to know what is in the roxicet that is not in the others that would cause this reaction.