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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- 1. Cairns R, Brown JA, Lynch AM, et al. A decade of Australian methotrexate dosing errors. Med J Aust 2016; 204: 384. <MJA full text>
- 2. Goldie JH, Price LA, Harrap KR. Methotrexate toxicity: correlation with duration of administration, plasma levels, dose and excretion pattern. Eur J Cancer 1972; 8: 409-414.
- 3. Kivity S, Zafrir Y, Loebstein R, et al. Clinical characteristics and risk factors for low dose methotrexate toxicity: a cohort of 28 patients. Autoimmun Rev 2014; 13: 1109-1113.
- 4. Chan BS, Dawson A, Buckley NA. What can toxicologists learn from therapeutic studies about the treatment of acute and chronic methotrexate poisoning? Clin Toxicol 2016; 54 S1: 479.
We thank the staff at the New South Wales Poisons Information Centre for recruiting patients with methotrexate poisoning.