Baricitinib: The Second FDA-Approved JAK Inhibitor for the Treatment of Rheumatoid Arthritis.

To review the pharmacology, pharmacokinetics, safety, and efficacy of baricitinib, a recently approved selective Janus Kinase (JAK) inhibitor for the treatment of rheumatoid arthritis (RA), and explore its potential role in therapy. Articles were identified using a PubMed search from inception through January 2019 using the terms , and , its molecular name. Articles relating to randomized clinical trials, pharmacology, pharmacokinetics, efficacy, and safety of baricitinib were evaluated. Baricitinib exerts its effects by inhibiting JAK1 and JAK2 enzymes, targeting cytokine and growth factor receptor stimulation, thus reducing downstream immune cell function. Four trials have demonstrated the efficacy of baricitinib with or without methotrexate in patients naïve to disease-modifying antirheumatic drugs (DMARDs) and those who had an inadequate response to or intolerance to both conventional and biological DMARDs. Furthermore, baricitinib was associated with delayed radiographic progression. Despite baricitinib 4 mg often demonstrating greater efficacy compared with the 2 mg dose, only the 2 mg dose is Food and Drug Administration approved because of safety concerns with the 4 mg dose, primarily thromboembolism. Baricitinib provides an oral treatment option for patients failing tumor necrosis factor inhibitors (TNFis). Safety, cost, and comparative effectiveness to tofacitinib should be considered prior to prescribing baricitinib. Baricitinib is the second medication in its class and has been proven efficacious for the treatment of RA. Given concerns for adverse effects associated with baricitinib, it should be reserved for patients who have failed one or more TNFis.