Impact of Prophylactic Trimethoprim-Sulfamethoxazole on Clearance of High-Dose Methotrexate in Adult Patients

High-dose methotrexate (HDMTX) is an antineoplastic dosing strategy used to treat various cancers including primary central nervous system lymphoma. Trimethoprim-sulfamethoxazole (TMP/SMX) is commonly used for antibiotic prophylaxis against Pneumocystis pneumonia infections in this patient population. Significant drug-drug interactions between TMP/SMX and methotrexate (MTX) leading to adverse outcomes have been documented, primarily in adult patients taking MTX for rheumatologic conditions.

This study is a single-center, retrospective, cohort study comparing outcomes in patients where TMP/SMX was held during HDMTX and patients who received concurrent prophylactic TMP/SMX during treatment. The primary end point was mean MTX level at 24, 48, and 72 hours. Secondary end points included rate of nonhematologic toxicity, rate of hematologic toxicity, median days to MTX clearance, and frequency of glucarpidase utilization.

In total, 248 cycles of HDMTX were analyzed from 221 individual patients. One hundred ninety-one cycles were administered without prophylactic TMP/SMX, and 57 were administered with TMP/SMX. The median MTX level at 24, 48, and 72 hours in those without versus with prophylactic TMP/SMX was 4.30 versus 4.30, 0.29 versus 0.30, and 0.14 versus 0.15, respectively. Similarly, rates of hematologic and nonhematologic toxicities did not differ significantly between groups with the exception of neutropenia; however, there was no corresponding increased rate of neutropenic fever. Only one patient received glucarpidase and had not received TMP/SMX.

Prophylactic TMP/SMX had minimal interaction with HDMTX and does not lead to increased time to clearance or clinically relevant toxicities. Prophylactic TMP/SMX can be safely administered with HDMTX in adult patients.