Cairns and colleagues1 noted in their article that eight deaths were identified as medication errors due to daily methotrexate dosing. In addition, 92 cases of methotrexate dosing errors were reported to the four Poisons Information Centres in Australia with a concerning rise in 2014–15. The authors found that low dose daily administration for 3–7 days could cause toxicity and even death.1 The toxicity of methotrexate is likely to be more dependent on the duration of exposure rather than on serum concentration.2 In a retrospective series of 28 patients, pancytopenia (79%) was found to be the most common manifestation of low dose chronic methotrexate toxicity.3 In contrast, in our study, we observed no effects with acute single dose exposures.4
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