A 5-day course of oral desensitization to trimethoprim/sulfamethoxazole (T/S) in patients with human immunodeficiency virus type-1 infection who werepreviously intolerant to T/S

Background: Trimethoprim/sulfamethoxazole (T/S) is an essential drug in pat ients with human immunodeficiency virus type-1 (HIV-1) infection to prevent opportunistic infections. About 40% to 60% of them develop skin rash which leads to discontinue the medication. A precise mechanism of the reaction i s not known. Objective: To make the patients more tolerable to the medication and to mak e clear whether or not the reaction is caused by serum sulfamethoxazole-spe cific IgE. Methods: We established a 5-day protocol, in which T/S was administered ora lly as a granular form in increasing doses beginning with 0.005 g (it conta ins trimethoprim 0.4 mg and sulfamethoxazole 2 mg) and doubled every 12 hou rs until the therapeutic dose was achieved. We tried to desensitize T/S in 17 patients with HIV-1 infection who were previously intolerant to T/S and measured the specific IgE in sera. Results: Desensitization was successfully completed in 15 (88.2%) of the pa tients. In two patients who failed the desensitization, one was due to feve r and the other was gastric irritation. During followup in a mean period of 16.6 months (range, 8 to 23 months) as of May, 1999, none has had Pneumocy stis carinii pneumonia (PCP) while receiving T/S after desensitization. Sul famethoxazole-specific IgE did not increase, indicating that it was not the major cause of skin rash due to T/S in our cases. Conclusion: These preliminary results show that most patients who were thou ght to be intolerant to T/S and had no sulfamethoxazole-specific IgE can be safely desensitized and received the drug subsequently as an effective pro phylaxis for PCP.