Thank you for your inquiry.
A quote from the most authoritative reference I could find dealing with this issue is copied for you below. This quote concerns non-Ige mediated reactions. The same would be true for Ige mediated events.
Allergies to sulfonamide antibiotics and sulfur-containing drugs
Donald A Dibbern Jr, MD and Anthony Montanaro, MD
Ann Allergy Asthma Immunol 2008; 100: 91-100.
Duration of Efficacy
"Once patients successfully complete a desensitization protocol and are finally able to tolerate standard daily doses of this drug, it must be continued throughout the treatment duration without missing a single daily dose. Within 24 to 48 hours of the last dose, medication resensitization can recur, and thus patients should be informed that they still remain allergic to these particular drugs (46).
The mechanisms of this resensitization for non–IgE-mediated drug allergy remain unknown at present. If a repeat course of similar therapy becomes necessary in the future, another desensitization procedure would again need to be performed before safely restarting use of this medication."
Thank you again for your inquiry and we hope this response is helpful to you.
Phil Lieberman, M.D.