Cytopenia induced by low-dose methotrexate: An analysis of 433 cases from the French pharmacovigilance database.

Introduction: Up to 5% of individuals exposed to low-dose methotrexate (MTX) (i.e., ≤30 mg/week) may develop cytopenia. However, MTX-induced cytopenia have been poorly described.

Material And Methods: All cases of cytopenia (i.e., anaemia, leukopenia, thrombocytopenia, bi- or pancytopenia) in patients receiving low-dose MTX reported to the French pharmacovigilance database during 2006-2016 were analysed. Three groups were defined: cytopenia due to MTX medication errors (e.g., daily rather than weekly administration), cytopenia in people receiving several medications including MTX, cytopenia in people receiving only MTX.

Results: 433 cases were analysed. Eighty-four cases (19.4%) were due to medication errors, 180 (41.6%) occurred in individuals exposed both to MTX and other drugs, and 169 (39.0%) occurred in individuals only exposed to MTX. By comparison to other patients, those with cytopenia due to medication errors were older (74 ± 13 vs 69 ± 15 years, p = 0.002), received more frequently MTX orally (92.9% vs 65.3%, p<0.001) and had more frequently pancytopenia (71.4% vs 54.4%, p = 0.005). By comparison to individuals exposed to multiple drugs (n = 180), those exposed only to MTX (n = 169) were older (71 ± 15 vs 67 ± 14, p = 0.02), and had more often pancytopenia (62.7% vs 46.7%, p = 0.001). Among those only exposed to MTX, most cases (n = 140, 82.8%) were considered as toxic rather than idiosyncratic reactions and a trigger (e.g. diarrhoea) was found in 59.3% of those cases. Overall 30 (6.9%) deaths occurred, including 8 in the "medication error" group and 8 in the "MTX only" group.

Conclusion: These data may be useful for defining optimal biological monitoring of patients prescribed low-dose MTX.