Objectives
Methotrexate (MTX), leflunomide (LEF) and sulfasalazine (SSZ) are conventional synthetic disease-modifying drugs (csDMARDs) with a well-established role in the treatment of rheumatoid arthritis. We aimed to estimate and compare the relative risks (RR) for adverse events (AEs) and the discontinuation due to AE of these drugs.
Methods
We included all 3339 patients from the NOR-DMARD study treated with MTX, LEF or SSZ in monotherapy. All reported AEs were compared between treatment groups using quasi-Poisson regression. In addition, drug retention rates were analysed using Kaplan-Meier estimates as well as Cox regression to control for possible confounders. We analysed drug retention rates and cumulative risk of discontinuation due to AE using the Kaplan-Meier estimator. We assessed age, gender, baseline disease activity score in 28 joints with erythrocyte rate (DAS28-ESR), seropositivity, prednisolone use, previous DMARD use, year of inclusion and comorbidity as possible cofounders.
Results
We found that the discontinuation rate due to AEs was significantly higher for LEF and SSZ than for MTX. After the first year it was 13.7% (95%CI 12.2–15.2), 39.6% (95% CI 34.8–44) and 43.4% (95% CI 38.2–48.1) for MTX, SSZ and LEF, respectively. Similar results were found when adjusting for confounders. The overall AE's was comparable across the treatment groups. AE profile was as expected for each drug.
Conclusion
Our work has shown a similar AE profile of csDMARD as previous data. However, higher discontinuation rates in SSZ and LEF cannot be easily explained from AE profiles.
Lay Summary
What does this mean for patients?
Rheumatoid arthritis is a chronic inflammatory condition that can affect joints throughout the body, leading to pain, stiffness, and swelling. It is essential to seek treatment early on to avoid long-term damage to the joints and to improve overall quality of life. We researched the risks of adverse events (i.e. undesired side effects) and drug discontinuation (i.e. stopping taking the drug) for three drugs that are commonly used to treat rheumatoid arthritis: methotrexate (MTX), leflunomide (LEF), and sulfasalazine (SSZ). In our data analysis from 3,339 patients treated with one of the three drugs, we found that more people stopped taking LEF and SSZ than MTX. However, it is important to note that adverse events were similar across the three treatment groups overall. The higher discontinuation rates in SSZ and LEF could not be easily explained by the type of adverse events experienced. The higher discontinuation rate could be due to differences in individual patient and doctor assessment of adverse events, psychosocial factors, and patient education. We suggest that further research is needed to identify other risk factors for adverse events, as well as ways to manage these risk factors.