Evaluation of sulfonamide detoxification pathways in haematologic malignancy patients prior to intermittent trimethoprim-sulfamethoxazole prophylaxis

AIMS Patients with haematologic malignancies have a reportedly high incidence of sulfamethoxazole (SMX) hypersensitivity. The objective of this study was to determine whether deficiencies in sulfonamide detoxification pathways, to include glutathione (GSH) and ascorbate (AA), and cytochrome b ₅ (b5) and cytochrome b ₅ reductase (b5R), were prevalent in these patients. A secondary pilot objective was to determine whether the incidence of drug hypersensitivity following intermittent trimethoprim-SMX (TMP-SMX) prophylaxis approached that reported for high dose daily regimens. METHODS Forty adult patients with haematologic malignancies (HM) and 35 healthy adults were studied; an additional 13 HM patients taking ascorbate supplements (HM-AA) were also evaluated. Twenty-two of 40 HM patients were prescribed and were compliant with TMP-SMX 960mg three to four times weekly. RESULTS There were no significant differences between HM and healthy groups in plasma AA (median 37.2μmvs. 33.9μm) or red blood cell GSH (1.9mmvs. 1.8mm). However, plasma AA was correlated significantly with leucocyte b5/b5R reduction (r= 0.39, P= 0.002). Deficient b5/b5R activities were not found in HM patients. In fact, patients with chronic lymphocytic leukaemia or myeloma had significantly higher median activities (80.7μmolmg ^-1min ^-1) than controls (18.9μmolmg ^-1min ^-1, P= 0.008). After 3-4 weeks of treatment, no patients developed SMX-specific T cells and only one patient developed rash. CONCLUSIONS Deficiencies of blood antioxidants and b5/b5R reduction were not found in this population with haematologic malignancies, and the development of skin rash and drug-specific T cells appeared to be uncommon with intermittent TMP-SMX prophylaxis.