['Pneumocystis jirovecii, formerly carinii, pneumonia (PCP) poses a life-threatening risk to oncology patients. The use of trimethoprim-sulfamethoxazole (TMP-SMZ) prophylaxis virtually eliminates the risk of infection; however, many patients cannot tolerate TMP-SMZ. We performed a retrospective analysis to determine the PCP breakthrough rate in pediatric oncology patients receiving intravenous pentamidine as second line PCP prophylaxis.', 'We conducted a retrospective chart review of pediatric oncology patients who received intravenous pentamidine from 2001 to 2006 at our institution. The diagnosis, age and bone marrow transplant (BMT) status were determined. A subset of patients had review of their records to determine the justification for discontinuing TMP-SMZ. Children who developed symptoms of pneumonia with a clinical suspicion of PCP underwent bronchoscopy, allowing for identification of Pneumocystis.', 'A total of 232 patients received 1,706 doses of intravenous pentamidine and no toxicities were identified. The main reasons for discontinuing TMP-SMZ were bone marrow suppression and drug allergy. Three children developed PCP, equating to a breakthrough rate of 1.3%. Two of these children had undergone BMT (1.9% breakthrough rate) and both were under the age of two (6.5% breakthrough rate).'] Is intravenous pentamidine effective as second line Pneumocystis pneumonia prophylaxis in pediatric oncology patients?