RESUMO
BACKGROUND: Intravenous high-dose methotrexate (MTX ≥ 1 g/m 2 ) is frequently used in patients with cerebral lymphoma or other malignancies. In addition to its potent efficacy, it is known to have pronounced toxicity and life-threatening side effects. Regular-level monitoring at short and defined intervals is mandatory. This study aimed to evaluate the possibility of replacing peripheral blood sampling with blood samples from central venous catheters for therapeutic monitoring of MTX in adults. METHODS: A total of 6 patients and 7 cycles of chemotherapy (6 females; 5 with cerebral non-Hodgkin lymphoma and 1 with osteosarcoma, median age 51 years; range 33-62 years) were included. An immunoassay was used for quantitative analysis of MTX levels. The measurement points were obtained in the time intervals of 24, 42, 48, and 72 hours, and afterward, every 24 hours until the level was below <0.1 µmol/L. After flushing with 10 mL of saline solution and discarding 10 mL of venous blood, blood was drawn from the central venous access through which MTX had previously been administered. Simultaneously, MTX levels were obtained from peripheral venipuncture. RESULTS: Methotrexate levels from central venous access and MTX levels from peripheral venipuncture showed a significant correlation (r = 0.998; P < 0.01; n = 35). During withdrawal from the central access group, 17 values showed a lower MTX level, 10 showed a higher level, and 8 showed no difference. However, the MTX level difference was not significant ( P = 0.997, linear mixed model). No increase in the dose of calcium folinate was necessary based on the collected MTX levels. CONCLUSIONS: In adults, MTX monitoring from central venous access is not inferior to monitoring from peripheral venipuncture. Repeated venipuncture to measure MTX levels can be replaced after establishing standardized instructions for proper sampling by a central venous catheter.