Disease-modifying antirheumatic drugs (DMARDs) are a class of drugs indicated for the treatment of rheumatoid arthritis (RA), which is a symmetric, inflammatory, polyarthritis of unknown etiology. These drugs are immunosuppressives designed to slow the damage done to joints, and they can induce or maintain remission, reduce the frequency of flare-ups, and allow for tapering of steroids while sustaining disease control. They can also be used to in the treatment of other autoimmune disorders such as scleroderma, vasculitis, spondyloarthritis, inflammatory myositis, inflammatory bowel disease, systemic lupus erythematosus, and some types of cancers.
There are 2 main types of DMARDs: traditional and biologics. Traditional DMARDs include methotrexate, leflunomide, hydroxychloroquine, and sulfasalazine. Others include cyclophosphamide, cyclosporine, and tacrolimus (FK506), but these are of limited use. Biologic DMARDs came to market in the early 1990s and are usually prescribed after evidence of disease progression and structural joint damage despite treatment with steroids and conventional therapy. Some biologic agents include abatacept, etanercept, infliximab, rituximab, tocilizumab, among others. These drugs are made of monoclonal antibodies, antibodies that are chimeric fusions, agents that are humanized, and some are receptors that have been fused to another part of the human immunoglobulin. Their design is highly specific and targeted to affect immune function. Additionally, Janus kinase (JAK) inhibitors such as tofacitinib, are also used in treatment. They are administered either intravenously or subcutaneously. Although many medications can be used in the treatment of RA, methotrexate is the most commonly used as an initial treatment.
In the treatment of rheumatoid arthritis, many factors come into play. Factors include severity of disease and disability, the location of the joint injury, comorbidities, patient preferences (including cost and frequency of monitoring), the presence of adverse prognostic signs, among others. Ultimately, treatment will include either monotherapy or a combination of therapies. A recent meta-analysis of 20, randomized, clinical trials studying the safety and efficacy of combination therapy throughout the years concluded that tocilizumab (an IL-6 receptor blocker) and methotrexate (a dihydrofolate reductase inhibitor) were the best combinations of medications for the treatment of rheumatoid arthritis. However, in cases where methotrexate is contraindicated or not tolerated, alternative non-biologics can be considered. These can include hydroxychloroquine or sulfasalazine. The goal of escalating therapy is to help slow joint damage. If these interventions remain unsuccessful, biologic DMARDs (etanercept, infliximab) can be considered. Joint damage can be seen very early in the disease course (as early as 2 years into the disease), so treatment should be initiated as soon as the diagnosis is made.
Prior to starting, resuming or significantly increasing the dosage of biologics or non-biologics, patients are screened for hepatitis B and C, especially if they have a history of intravenous drug abuse or if they exercise high-risk sexual behaviors. In other cases, a PPD skin test or an interferon-gamma release assay is conducted to establish a baseline for latent tuberculosis infection. A baseline chest x-ray should also be done, as some of these meds can cause interstitial lung disease.
The class of DMARDs is extensive, and traditional DMARDs act via various mechanisms. They interfere in combinations of critical pathways in the inflammatory cascade. Methotrexate, for example, stimulates adenosine release from fibroblasts, reduces neutrophil adhesion, inhibits leukotriene B4 synthesis by neutrophils, inhibits local IL-1 production, reduces levels of IL-6 and IL-8, suppresses cell-mediated immunity, and inhibits synovial collagenase gene expression. Other medications in this class serve to inhibit proliferation or cause dysfunction of lymphocytes.
Biologics, on the other hand, are very selective in their mechanism of action. The overarching functional of biologics include (1) interfering with cytokine function or production, (2) inhibiting the “second signal” required for T-cell activation, and (3) depleting B-cells or inhibiting factors that active B-cells (rituximab and belimumab). Tofacitinib is a small molecule inhibitor of JAK, a protein tyrosine kinase involved in mediating cytokine signaling.
DMARDs (biologics and non-biologics) can be administered orally or intravenously (IV).
DMARDs are very powerful drugs which modulate sequences in the immune system. Their adverse effects can range from mild (rash, nausea, vomiting, stomatitis) to severe, life-threatening infections; therefore, frequent monitoring is required. As a group, conventional DMARDs can cause gastrointestinal (GI) distress, bone marrow suppression, neutropenia, interstitial lung disease, and hepatotoxicity. Methotrexate has been known to cause neurotoxicity, pneumonitis and liver disease including cirrhosis. Of note, a recent study suggests methotrexate (in combination with bisphosphonates) is a risk-factor for bisphosphonate-induced osteonecrosis of the jaw. In another case, hydroxychloroquine (HCQ) can cause retinopathy (macular damage) and rash. Leflunomide can cause diarrhea, alopecia, and elevated liver transaminases.
Biologic agents also have increased the risk of fatal viral, bacterial, and/or fungal infections. Reactivation or primary viral infections of herpes zoster or hepatitis B/C is also common. Specifically, the anti-CD20 (rituximab) and IL-1 receptor antibody can cause possible congestive heart failure and demyelinating central nervous system (CNS) disease. JAK inhibitors can cause elevated creatinine, LFTs, and hypertension. Cyclosporine can cause nephrotoxicity, hypertension, and gum hyperplasia on rare occasions.
Life-threatening adverse effects of these meds warrant immediate suspension of the drugs.
DMARDs are not to be taken by patients who have an active infection, those with preexisting bone marrow hypoplasia, leukopenia, chronic liver disease, or immunodeficiency syndromes. Methotrexate is contraindicated in pregnancy.
High dose methotrexate is delivered IV and is used over 4 to 36 hours for CNS prophylaxis in patients with leukemia, high-risk lymphomas, osteosarcomas, among others, and for eradicating leptomeningeal spread. Because such a powerful dose is used, a "leucovorin rescue" is used to terminate the toxicity of the drug on the kidneys.