Thank you for your question. I was not able to find a clear cut rationale for one challenge protocol over the other. We did ask Dr Macy for his thoughts: "A challenge with a single co-trimoxazole single-strength tablet and 5 days of follow-up is adequate to confirm current tolerance and the absence of serious T-cell mediated hypersensitivity. This has been the standard practice in our group for several years. Expect about 10% of challenged individuals to have a recurrent rash, similar to the index event. It is not possible to desensitize individuals with a clinically significant T-cell mediated hypersensitivity, but rechallenges are often uneventful. Multiple dose challenges add nothing diagnostically. "
I hope this is helpful.
Andrew Murphy, MD, FAAAAI