Pediatric Rheumatology Online Journal → June 2003 → Methotrexate→ Abstract #46

LONG TERM MONITORING OF METHOTREXATE (MTX) TOXICITY IN CHILDREN WITH JUVENILE IDIOPATHIC ARTHRITIS (JIA) SUGGESTS THAT GUIDELINES FOR FREQUENCY OF BLOOD TEST MONITORING SHOULD BE MODIFIED

O. Ortiz-Alvarez,¹ G. Avery,¹ J. Green,¹ R. E. Petty,¹ L. B. Tucker,¹ P. N. Malleson,¹ D. A. Cabral.¹

¹Rheumatology, British Columbias Childrens Hospital, Vancouver, BC, Canada

The risk of bone marrow suppression and hepatic toxicity from the MTX doses used in treatment of arthritis is not clear. Adult patient guidelines recommend 4-6 weekly blood test monitoring for these side effects. As blood testing is a burden for many children, guidelines for monitoring should reflect the specific risk of toxicity for children. Aims: To describe, for a cohort of children with JIA on MTX, the long term experience of MTX toxicity identified by routine monthly bloods tests. Methods: Since1999 all patients on, or starting MTX were monitored by a protocol to identify and respond to significantly abnormal blood tests (SABT) defined: Abnormal low granulocyte and lymphocyte counts - age specific laboratory standards; low hemoglobin - a drop of 1 gm between tests; elevated liver enzymes - greater than 2 times the upper level of normal for the testing laboratory. SABT identified from our database, and subsequent interventions were documented. Suspected reasons for SABT were recorded. Results: 71 patients (25 oligo, 25 poly, 7 syst., 5 psor., 8 enthesitis rel., 1 unclass.) used MTX for a mean of 28.4m (range 1.4101m) for a total of 2013 patient-months of monitoring. The mean maximum dose was 14 mg/m (range 6-25mg/m). 26 patients had at least one SABT and the episodes occurred at mean of 15.9m (range 1-53m) after treatment onset. There was 45m of monitoring / SABT-episode. The frequency of abnormalities were lymphopenia 8(31%), high AST, ALT 7(27%), 3(11.5%); anemia, 3(11.5) neutropenia. Interventions for SABT were: earlier repeat test only 11(42%); stopped MTX for 1-4w 7(27%); and stopped the MTX indefinitely 1(4%). SABT was associated with viral syndrome in 8 cases (31%), in 3 (12%) the SABT were thought to be disease related, no attributable causes were described in 13 cases (50%). Conclusions: Monthly blood test monitoring for MTX toxicity in children with JIA may be too frequent.