AbstractBackgroundTaiwanese patients frequently experience severe hepatotoxicity associated with high‐dose methotrexate (HD‐MTX) treatment, which interferes with subsequent treatment. Drug–drug interactions occur when MTX is used in combination with proton pump inhibitors (PPIs), trimethoprim‐sulfamethoxazole (TMP‐SMX), or non‐steroidal anti‐inflammatory drugs (NSAIDs). In East Asia, real‐world analyses on the effects of co‐medication and other potential risk factors on the clinical course of HD‐MTX‐mediated acute hepatotoxicity in patients with osteogenic sarcoma (OGS) are limited.MethodsThis cohort study included patients with newly diagnosed OGS who were treated with HD‐MTX between 2009 and 2017 at Taipei Veterans General Hospital. We collected data on the clinical course of HD‐MTX‐mediated acute hepatotoxicity, co‐medications, and other potential risk factors, and analyzed the effects of these factors on the clinical course of HD‐MTX‐mediated acute hepatotoxicity.ResultsAlmost all patients with OGS treated with HD‐MTX developed acute hepatotoxicity with elevated alanine aminotransferase (ALT) levels. Most patients with Grade 3–4 ALT elevation failed to recover to Grade 2 within 7 days. Women and children are high‐risk subgroups for HD‐MTX‐mediated elevation of ALT levels. Age is a factor that contributes to the pharmacokinetic differences of HD‐MTX. However, the concurrent use of PPIs, TMP‐SMX, or NSAIDs did not affect the elimination of MTX when administered with adequate supportive therapy.ConclusionsCo‐administration of PPIs, TMP‐SMX, or NSAIDs may have limited effects on acute hepatotoxicity in well‐monitored and adequately pre‐medicated patients with OGS undergoing chemotherapy with HD‐MTX. Clinicians should pay particular attention to ALT levels when prescribing HD‐MTX to children and women.