BACKGROUND

Conventional synthetic disease-modifying anti-rheumatic drugs (DMARDs) are the preferred first-line treatment in patients with psoriatic arthritis, although there is a paucity of evidence for the efficacy of conventional synthetic DMARDs and especially their combination. We aimed to investigate whether a combination of methotrexate plus leflunomide is superior to methotrexate monotherapy at improving disease activity in patients with psoriatic arthritis.

METHODS

This single centre, investigator-initiated, double-blind, randomised, placebo-controlled trial was conducted at Sint Maartenskliniek in the Netherlands (locations included Boxmeer, Geldrop, Woerden, and Nijmegen). Patients aged 16 years or older with a clinical diagnosis of psoriatic arthritis and active disease (defined as two or more swollen joints; dactylitis counting as one swollen joint) were included. Patients were randomly allocated (1:1) and stratified by high disease activity (psoriatic arthritis disease activity score [PASDAS] ≥5·4) to either methotrexate plus leflunomide (combination therapy) or methotrexate plus placebo (monotherapy), using computer-generated stratified variable block randomisation. In both groups, patients received oral methotrexate 15 mg per week for the first 4 weeks and 25 mg per week thereafter combined with two leflunomide 10 mg tablets once per day or two placebo tablets. During the study period, the patients, nurses, researchers, and treating physicians were all masked to treatment allocation. The primary outcome was the difference in mean PASDAS at week 16, adjusted for baseline PASDAS, between the combination and monotherapy groups, assessed in the intention-to-treat population. This trial was registered with the Netherlands Trial Register (NL7404) on Dec 3, 2018.

FINDINGS

Between Feb 19, 2019, and March 11, 2021, 82 patients were screened for eligibility. Four patients were ineligible and 78 were enrolled and randomly assigned to either methotrexate plus leflunomide (n=39) or methotrexate plus placebo (n=39). 50 (64%) of 78 patients were male, 28 (36%) were female, and the median age of patients was 55·0 years (IQR 42·0-64·0). Methotrexate plus leflunomide combination therapy was superior to methotrexate monotherapy at week 16 (PASDAS 3·1 [SD 1·4] vs 3·7 [SD 1·3]; treatment difference -0·6, 90% CI -1·0 to -0·1; p=0·025). There were no study deaths. The most frequently occurring adverse events were nausea or vomiting (17 [44%] of 39 patients in the methotrexate plus leflunomide group vs 11 [28%] of 39 in the methotrexate plus placebo group), tiredness (9 [23%] vs 13 [33%]) and elevated alanine aminotransferase (12 [31%] vs 7 [18%]. Generally, the incidence of mostly mild adverse events was higher in the methotrexate plus leflunomide group than in the methotrexate plus placebo group.

INTERPRETATION

Methotrexate plus leflunomide combination therapy results in greater improvement in disease activity according to PASDAS in patients with psoriatic arthritis. However, methotrexate plus leflunomide combination therapy is less well tolerated than methotrexate monotherapy.

FUNDING

Regional Junior Researcher Grant from the Sint Maartenskliniek.