Objective: To determine which risk factors are associated with serious pancytopenia associated with low dose methotrexate (MTX) therapy.
Methods: All Ottawa area rheumatologists, hematologists and dermatologists were surveyed to obtain cases of pancytopenia associated with low dose MTX therapy between 1981 and 1991. Pancytopenia was defined as white blood cells < 3.5 x 10(9)/l and platelets < 140 x 10(9)/l and hemoglobin < 100 g/l. A case control method was used to evaluate risk factors.
Results: Fifteen cases of pancytopenia were identified from returned questionnaires (93% response rate) and from reviewing the medical records of 2 major teaching hospitals. All patients were hospitalized, had MTX therapy discontinued and were treated: 12 patients received transfusions, 8 leucovorin therapy, and 4 folic acid. Two patients died, only 1 directly due to MTX therapy. Identified risk factors were (1) elevated BUN or creatinine levels, (2) increasing mean corpuscular volume values, (3) increased age and (4) concomitant trimethoprim-sulfamethoxazole therapy.
Conclusions: Pancytopenia associated with low dose MTX therapy is a life threatening adverse effect often associated with known risk factors. A change in monitoring guidelines and patient education are suggested as means of risk reduction.