Mycophenolate Mofetil (MMF) for Myositis

How does MMF work?

In myositis, parts of the immune army become overactive and begin multiplying rapidly, attacking healthy tissues such as muscles, skin, and sometimes the lungs.

MMF works by putting a “speed limit” on specific immune cells called lymphocytes (T cells and B cells), which drive inflammation.

• Slows down the production of new inflammatory immune cells
• Reduces the number of immune cells attacking muscles and lungs
• Lowers ongoing inflammation
• Helps prevent long-term tissue damage

Uses

• Myositis (especially with lung involvement)
• Systemic lupus erythematosus (SLE)
• Vasculitis and other autoimmune diseases
• Prevention of organ transplant rejection

Why is MMF important in myositis?

MMF is commonly used as a steroid-sparing medicine, meaning it helps control disease while allowing steroid doses to be reduced over time.

• Lung involvement (interstitial lung disease) is present
• Skin disease is difficult to control
• Steroid side effects are a concern
• Additional long-term disease control is needed

How is MMF taken?

MMF is usually taken twice daily as tablets, capsules, or oral suspension. Try to take it at approximately the same times each day.

Common side effects

Many people tolerate MMF well, especially after the first few weeks. Common side effects include loose stools or mild diarrhoea, nausea, stomach discomfort, abdominal pain, and mild fatigue.

Taking the medicine with food, splitting the doses properly, or switching to a specially coated version of the tablet (mycophenolic acid) often helps calm the stomach.

Why are blood tests necessary?

MMF can occasionally affect white blood cell counts, red blood cells and platelets, liver function, and kidney function. Monitoring may include complete blood count, liver function tests, and kidney function tests.

Missed dose

Take the missed dose as soon as you remember. If it is almost time for the next dose, skip the missed dose and continue your regular schedule. Do not take two doses together.

During infection

Contact your healthcare team if you develop high fever, a significant infection, or hospital admission. Your doctor may advise temporarily stopping MMF until the infection improves.

Because MMF lowers your defence army, practise good hand hygiene and avoid close contact with people who are actively sick with contagious infections.

Pregnancy, breastfeeding, and vaccines

Inactivated vaccines are generally safe. Flu and pneumococcal vaccination may be recommended. Live vaccines should usually be avoided while taking MMF.

Pregnancy must be avoided while taking MMF. MMF can cause serious birth defects and pregnancy loss.