Dermatological guidelines for monitoring methotrexate treatment reduce drug-survival compared to rheumatological guidelines

Background: Methotrexate (MTX) is widely used as disease modifying treatment for psoriasis and psoriatic arthritis (PsA). Rheumatological and dermatological guidelines to prevent MTX-induced adverse events diverge in the number and frequency of blood tests. These differences are not based on evidence indicating a higher risk for patients with psoriasis compared to PsA or rheumatic arthritis (RA). This raises the question if multiple testing increases safety, or results in false positive signals potentially leading to early withdrawal of an effective treatment. Objective: Compare the effects of MTX monitoring strategies by rheumatologists and dermatologists regarding drug survival, reasons for withdrawal and safety. Methods: Retrospective follow-up of all patients diagnosed with psoriasis by dermatologists or PsA by rheumatologists. Included were consecutive patients who started methotrexate (MTX) between 2006 and 2012 and had a scheduled follow-up by dermatologist or rheumatologist. Exclusions were: drug not started after the first prescription or incomplete availability of lab data. Data were extracted from electronic records: start and stop dates and dosing of MTX; treatment with folic acid and dose; reasons for withdrawal of MTX; numbers of blood sampling and types of laboratory tests performed for MTX safety; number of abnormal tests; occurrence of any serious adverse event (SAE). Results: 190 Psoriasis and 196 PsA patients starting methotrexate (MTX) were included. Age and sex were comparable. PsA patients used higher initial and maximum doses of MTX and folic acid, but psoriasis patients had a higher frequency of abnormal laboratory results (0.14 vs 0.03 per treatment month, p