Immunosuppressants are drugs that inhibit or prevent activity of the immune system. In addition to treating many autoimmune diseases, they are also used to prevent organ transplant rejection, as chemotherapy for cancer treatment, and as treatments for other conditions.

In treating myositis diseases, immunosuppressants are often introduced as second-line medications or used in combination with prednisone. This allows patients to taper off prednisone more quickly and avoid some of the unwanted effects. The choice of which immunosuppressant is used depends on the patient’s symptoms and what medications target those symptoms. Different drugs may be added or changed, depending on how well symptoms are being controlled.

Keep in mind that all immunosuppressants carry an increased risk of infection, because they dampen the body’s response to attacks from microorganisms such as bacteria and viruses.

The following immunosuppressants are currently used to treat myositis diseases.

Methotrexate was developed as a cancer treatment in the 1940s, but it has since become one of the most common medications used, in much smaller doses, to treat rheumatoid arthritis, another autoimmune disease. It can be taken orally (in pill form or liquid) or by injection (either under the skin or into the muscle). Symptoms may take two to three months to resolve.

Methotrexate is not intended to be taken every day; most people take it only once a week at a dose of 15-25mg/week. Taking this medication every day may cause severe side effects and overdosage.

GI problems, such as nausea and vomiting, are the most common side effects associated with methotrexate. Some patients experience hair loss, and some develop mouth ulcers or sores. Some Patients also complain of “methotrexate fog” on the day after they take their dose, which may include headaches, fatigue, and an overall “blah” feeling. The good news is that these side effects can usually be avoided by taking a folic acid (1mg/day) supplement.

Patients who also have interstitial lung disease should probably avoid methotrexate, since it comes with a risk of pulmonary fibrosis.

Azathioprine (Imuran) is also used to treat rheumatoid arthritis and as an antirejection medication for people who have had a kidney transplant. In myositis, it is usually taken orally (by mouth), and is best taken with food to avoid stomach upset. Doses are usually started at 50mg twice daily, then increased by 50mg every two to four weeks.

It may take up to six months for symptoms to improve. This medication also has an effect on the blood clotting mechanism in the body, so you may notice that you bruise more easily, and it may take longer for a wound to stop bleeding.

Azathioprine may be a better choice for some patients who have interstitial lung disease.

Mycophenolate mofetil (CellCept) is also used to prevent rejection in organ transplant patients and to treat other autoimmune diseases. In myositis, it is usually taken orally (by mouth) at a dose of 250-500mg twice per day, increasing gradually to a dose of 2,000-3,000mg per day. Patients with kidney problems should use a lower dose.

Mycophenolate mofetil has been used with good results in patients who have interstitial lung disease and in difficult to treat dermatomyositis skin disease, especially in combination with prednisone or other immunosuppressants.

Side effects may include GI upset, joint pain, fatigue, headache, cough, and/or breathing issues.

Cyclosporine is a natural product derived from a fungus. It is used to prevent rejection in organ transplant patients and to treat other autoimmune diseases. It is used as a second-line treatment in myositis, especially for patients who have interstitial lung disease (ILD).

Cyclosporine is taken orally, starting at 50mg twice a day and increase gradually to 100-150mg twice daily.

Side effects include nausea, cough, fatigue, fever, high blood pressure, back pain, abdominal pain, and hair loss. It can also be toxic to the kidneys and nervous system.

Tacrolimus (Prograf) is another drug that was developed as an antirejection medication for organ transplants. It works by inhibiting the production of interleukin-2 (IL-2), a molecule that promotes the development and proliferation of T cells in the immune system. It is used as a second-line treatment in myositis, especially for patients who have interstitial lung disease (ILD).

Tacrolimus is taken orally at a dose of 1mg twice daily and increased slowly until optimal blood levels are achieved.

Side effects are similar to cyclosporine.

Cyclophosphamide (Cytoxan) was developed as a chemotherapeutic agent to treat cancer. It is also used as an antirejection medication for organ transplants. Because it can be fairly toxic, its use in myositis is limited to very refractory cases with interstitial lung disease (ILD).

Most people develop side effects when taking cyclophosphamide. Common side effects include low white blood cell counts, loss of appetite, vomiting, hair loss, and bladder complications. Other severe side effects include an increased future risk of cancer, infertility, allergic reactions, and pulmonary fibrosis.

Cyclophosphamide is given orally or intravenously. The oral dose is 2mg/kg per day.

Hydroxychloroquine (Plaquenil) is an antimalarial drug that also has anti-inflammatory qualities and is used to treat certain autoimmune diseases, including rheumatoid arthritis and Sjögren’s disease.

Hydroxychloroquine is take orally (by mouth). Common side effects include vomiting, headache, changes in vision, and muscle weakness. Severe side effects may include allergic reactions.