RESUMO
BACKGROUND: High-dose methotrexate (HDMTX) therapy is a key component of many chemotherapy protocols. However, some patients develop HDMTX-induced nephrotoxicity. Carboxypeptidase-G2 (CPDG2) hydrolyses MTX into 2,4-diamino-N10-methylpteroic acid (DAMPA) and glutamic acid, and is used as a rescue agent in patients with nephrotoxicity and delayed elimination. Despite the frequency of HDMTX-induced renal injury, crystalluria is uncommon. Furthermore, crystals are rarely identified by conventional chemical methods. OBJECTIVE: To determine the composition of crystalluria in a patient with osteosarcoma who was treated with CPDG2. METHODS: Crystalluria was evaluated by optical microscopy, and chemical identification was performed by Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and Orbitrap™ high-resolution mass spectrometry (HRMS). RESULTS: The HRMS spectra of the patient's urine sediment showed a main peak at m/z 326.13, corresponding to the molecular mass of DAMPA [(C15H15O2N7)â¯+â¯H+]. The FT-IR spectral patterns of the sediment and DAMPA were not identical. SEM was unable to identify the crystal. CONCLUSION: DAMPA crystalluria was identified by Orbitrap™ HRMS in a patient treated with CPDG2 after HDMTX nephrotoxicity. This case reinforces the need to implement adequate measures to prevent nephrotoxicity. In cases of HDMTX-induced nephrotoxicity, urine sediment analysis should be requested.
