Safety and efficacy of metformin in systemic lupus erythematosus: a multicentre, randomised, double-blind, placebo-controlled trial

Background Immunometabolism is involved in the pathogenesis of systemic lupus erythematosus (SLE). The aim of this study was to repurpose metformin, an anti-diabetic drug that regulates systemic and cellular metabolism, and assess its effects in Chinese patients with SLE without diabetes. Methods We did a multicentre, randomised, double-blind, placebo-controlled trial in three hospitals in Shanghai, China. We enrolled adult patients with SLE, without diabetes, who had Safety of Estrogens in Lupus Erythematosus National Assessment-Systemic Lupus Erythematosus Disease Activity Index (SELENA-SLEDAI) scores no higher than 6; with no A score or no more than one B score on the British Isles Lupus Assessment Group (BILAG) scale at screening; who had had at least one lupus flare; and were treated with prednisone (a20 mg per day) within the preceding 12 months. Patients were randomly assigned (1:1) in blocks of four by a computer algorithm to add metformin tablets (250 mg per tablet with a target dose of 0.5 g three times per day; metformin group) or placebo tablets (placebo group) to their standard therapy, for a maximum of 12 months. Patients, assessment staff, and statisticians were masked to group assignment. The primary endpoint was a composite index of major or mild-to-moderate disease flares (S ELENASLEDAI Flare Index) at 12 months. The full analyses were done in all patients who received at least one dose of the study drug using the chi(2) test. Adverse events were recorded during the 12-month follow-up. This study is registered with ClinicalTrials.gov, NCT02741960. Findings Between May 24, 2016, and Dec 13, 2017, 180 patients were screened, of whom 140 (78%) of them were enrolled. 31 (17%) did not meet the inclusion criteria and nine (5%) withdrew informed consent without treatment after randomisation. 67 patients were assigned to the metformin group and 73 to the placebo group. By 12 months of followup, there was no significant difference in the incidence of lupus flares, which occurred in 14 (21%) patients in the metformin group versus 25 (34%) in the placebo group (relative risk 0.68, 0.42-1.04, p=0.078). Patients receiving metfonnin experienced more gastrointestinal adverse events (three [4%] discontinued for this reason vs one [1%] for placebo; overall 26 [39%] vs 11 [15%], p=0.0015), but the incidence of non-flare serious adverse events was similar between groups (one [1%] vs three [4%], p=0.35). The frequency of infection events was significantly lower in patients in the metformin group than in the placebo group (17 [25%] vs 32 [44%], p=0.022). No patients died as a result of treatment. Interpretation This trial was underpowered to draw a sound condusion on the efficacy of metformin to reduce disease flares as an add-on treatment to standard care in patients with SLE. Nonetheless, metformin had a favourable safety profile and our data present a basis for larger trials to investigate its potential effect on reducing the frequency of flares for patients with SLE with low-grade disease activity who are at risk of relapse. Copyright (C) 2020 Elsevier Ltd. All rights reserved.