Measuring transaminases in patients with rheumatoid arthritis on weekly methotrexate: does timing of blood testing matter?

The change in transaminase levels over a single week during therapy with methotrexate (MTX) has not been investigated or reported to date. In clinical practice, it is common to observe abnormal transaminase levels upon routine blood work for toxicity monitoring. Many have suggested that such lab abnormalities can sometimes be attributed to sampling blood for toxicity monitoring proximately following MTX dosing. The aim of our study was to evaluate changes in transaminase levels (AST/ALT) over 1 week after MTX administration in rheumatoid arthritis (RA) patients. In this small proof of concept study, we evaluated 13 patients with RA taking stable doses of methotrexate and background medications (e.g., NSAIDs and prednisone), but no other disease-modifying anti-rheumatic drugs (DMARDs). All patients were on a stable dose of folic acid. Patients received their usual doses of MTX administered at a specified time, and then sequential blood samples were obtained over the course of 7 days. Peripheral blood was obtained at each time point to measure serum transaminases. We did not observe any significant change in sequential transaminases over 1 week in relationship to MTX administration. It is possible that MTX therapy alone does not lead to significant weekly transaminase variations, contrary to our clinical expectations. The addition of other medications (i.e., NSAIDs) to stable MTX regimen may result in transaminase abnormalities.