Pneumocystis jiroveci pneumonia prophylaxis during maintenance therapy influences methotrexate/6-mercaptopurine dosing but not event-free survival for childhood acute lymphoblastic leukemia

Trimethoprim‐sulfamethoxazole (TMP/SMX) is used in children with acute lymphoblastic leukemia (ALL) to prevent Pneumocystis pneumonia (PCP). We explored to which extent TMP/SMX influenced methotrexate (MTX)/6‐mercaptopurine (6MP) dosage, myelosuppression, and event‐free survival (EFS) during maintenance therapy. Of 447 study patients treated by the NOPHO ALL92 protocol, 120 patients received TMP/SMX continuously for 2–7 d/wk (TMP/SMX2–7) and 287 patients never received TMP/SMX (TMP/SMXnever). Ten patients (all TMP/SMXnever) developed PCP, eight of which occurred within 7 months from the start of maintenance therapy. The TMP/SMX2–7 group received lower oral 6MP doses than TMP/SMXnever patients (50.6 vs. 63.9 mg/m2/d; P