Desensitization to co-trimoxazole (trimethoprim-sulphamethoxazole) in HIV-infected patients: Is patch testing a useful predictor of reaction?

Objective: to establish the safety and efficacy of desensitization to co-tr imoxazole in hypersensitive HIV-infected subjects. To assess if delayed hyp ersensitivity (type IV) to co-trimoxazole predicts those unable to be desen sitized. Method: desensitization to co-trimoxazole, comprising trimethoprim (T) 0.4 mg and sulphamethoxazole (S) 2 mg initially with doubling dose daily, full strength co-trimoxazole (T/S 160 mg/800 mg) at 10 days. Patch testing with 4.5% and 9% co-trimoxazole in yellow soft paraffin, CMI Multitest. Results: nineteen patients, 18 male and one female, were recruited and comp leted the desensitization regime. Of these 80% (15) achieved successful des ensitization. Three of those who reacted did so within 18 days. All patient s were successfully managed in an outpatient setting. There were no major a dverse reactions, Of those reacting none gave a positive patch test to co-t rimoxazole and all showed absent delayed type hypersensitivity reactions to recall antigens, Conclusions: co-trimoxazole desensitization is a safe and efficacious proce dure, with a success rate of 80% using the above regime. Patch testing with co-trimoxazole gives no useful information about those that reacted.