M Toronto Myositis Centreat St. Michael's Hospital
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Rituximab

Rituxan and biosimilars · say “ri-TUX-i-mab”
B-cell therapy (lab-made antibody)
iUsed in myositis based on specialist experience and evidence, not a formal Canadian myositis approval.
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Screened before you start.

You are checked for hepatitis B before rituximab, because the treatment can reactivate a past infection. This screening is essential.

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What it is

A targeted antibody for tougher disease.

Rituximab is a lab-made antibody that removes a type of immune cell called the B cell, which helps drive myositis. It is given by infusion and is used for myositis that has not responded to first-line treatment, for antisynthetase syndrome, and when the lungs are involved. It is used in myositis based on specialist experience and evidence rather than a formal Canadian myositis indication.

How to take it
  • Given by IV infusion in a hospital or infusion centre, by a trained nurse.
  • A course is usually two infusions two weeks apart, then repeated about every 6 months depending on your response.
  • You are given pre-medications (such as acetaminophen, an antihistamine, and sometimes a steroid) to reduce infusion reactions.
  • The first infusion is given slowly, since reactions are most likely then.
What to expect
  • It works gradually over weeks to months as B cells are removed.
  • Benefit often lasts several months, which is why re-dosing is spaced out.
  • Your doctor tracks your strength, CK, and (if relevant) lung tests to judge the response.
Benefits

How it helps you.

Effective in stubborn disease

A valuable option when first-line treatments have not controlled myositis.

Helps antisynthetase and lung disease

Often chosen for antisynthetase syndrome and for myositis-related lung involvement.

Steroid-sparing

Can allow prednisone to be tapered.

Infrequent dosing

Given roughly twice a year rather than daily.

Well established

Used for many years across autoimmune diseases.

Targeted action

Removes the specific immune cells that contribute to disease.

Risks & side effects

What you should know.

Your doctor prescribed this because the expected benefits outweigh the risks for your situation. Here is the honest, full picture.

Common side effects
Infusion reactions
Chills, fever, flushing, or itch during the first infusion. Slowing the rate and pre-medication usually settle it.
Higher infection risk
Especially of the airways. Report fevers and persistent coughs.
Fatigue
Feeling tired for a day or two after an infusion.
Serious but uncommon
Hepatitis B reactivation
If you have had hepatitis B, it can reawaken. You are screened before starting, and treated to prevent this if needed.
Low immunoglobulins
Repeated courses can lower antibody levels over time, raising infection risk. Monitored by blood tests.
Serious infections
Rarely, severe infections. Report fevers or feeling very unwell.
PML (brain infection)
Very rarely, a serious brain infection. Report new confusion, vision changes, weakness, or trouble with speech or balance.
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Hepatitis B screening comes first.

Rituximab can reactivate a past hepatitis B infection, which can be serious. You are screened before your first dose, and if needed you are given a protective antiviral. Make sure your team has your hepatitis results before you start.

Staying safe

Monitoring and precautions.

Regular monitoring
  • Hepatitis B (and often hepatitis C) screening before starting.
  • Blood counts and immunoglobulin levels are checked, especially with repeat courses.
  • Infection watch between courses, since protection against infection can be reduced.
  • Your strength, CK, and lung tests guide when to re-dose.
Daily precautions
  • Get vaccines up to date before starting where possible, since they work less well afterward.
  • Avoid live vaccines; flu and COVID vaccines are safe but timed around your infusions.
  • Report infections early, and tell providers you have had rituximab.
  • Wash hands often and avoid close contact with people who are sick.
When to call your doctor

Contact the clinic if you notice:

Infusion reaction
Chills, fever, rash, throat tightness, or breathlessness during or soon after an infusion. Tell the nurse at once.
Fever or signs of infection
Any fever, persistent cough, or feeling very unwell. Report promptly.
Neurological changes
New confusion, vision changes, weakness, or trouble with speech or balance. Report urgently.
Yellowing skin or dark urine
May signal hepatitis reactivation. Report promptly.
New or worsening weakness
May signal that disease is returning and re-dosing is due.
Before other vaccines
Check timing with your team, since vaccines work best away from infusions.

Pregnancy & breastfeeding

Rituximab is generally avoided in pregnancy, and effective contraception is advised during treatment and for up to 12 months after the last infusion. Tell your doctor if you are pregnant or planning, so the timing and choice of treatment can be reviewed.

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This guide is for education, not medical advice. Myositis treatment is individual, and many of these medications are used based on specialist experience and evidence rather than a formal Canadian myositis indication. Never start, stop, or change a medication without your own doctor. Your doses and choices are decided with your care team at the Centre.

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