BACKGROUND AND AIMS: Hepatotoxicity is a known risk of oral and intravenous methotrexate (MTX), but whether intrathecal (IT) administration causes hepatotoxicity remains unknown. We aimed to explore whether IT-MTX causes acute hepatoxicity. METHODS: Retrospective single-centre analysis of all patients treated with IT-MTX from 2000 to 2020. We compared liver enzymes (LE) at baseline (within 7 days before IT-MTX) to post-MTX (within 7 days after IT-MTX). LE elevation was defined as ≥ 50% increase in LE from baseline and greater than upper limit of normal. Drug-induced liver injury (DILI) was defined based on established criteria. RESULTS: A total of 270 patients (184 adults and 86 paediatric) received IT-MTX and had available LE data. Aminotransferase elevation was seen post-MTX in 107 (40%) patients, of whom 96 (36%) had ALT and 68 (25%) had AST elevation. DILI occurred in 16 (6%) patients. Aminotransferases peaked a median of 4 (3-5) days post-MTX, returning near baseline by day 7. Paediatric patients had higher incidence of aminotransferase elevations and DILI than adults (ALT 51% vs. 28%
AST 41% vs. 18%
DILI 11% vs. 3%
p <
0.01 for all). No significant predictors of LE elevation or DILI were identified, and no patient developed liver failure. The severity of ALT elevation after the first IT-MTX dose did not predict severity of a subsequent dose. CONCLUSION: Acute transient aminotransferase elevation is common after IT-MTX, especially in paediatric patients. Only a fraction of patients developed DILI, which was self-limited with no sensitisation or liver failure.