M Toronto Myositis Centreat St. Michael's Hospital
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Cyclophosphamide

Procytox, Cytoxan · say “sye-kloh-FOSS-fa-mide”
Potent immunosuppressant
iUsed in myositis based on specialist experience and evidence, not a formal Canadian myositis approval.
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For severe disease, used for a set time.

Cyclophosphamide is a strong medication reserved for severe or rapidly progressing disease, often the lungs. Bladder protection and fertility are discussed before you start.

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What it is

A powerful option for organ-threatening disease.

Cyclophosphamide is a potent immunosuppressant used for severe myositis, particularly rapidly progressive lung disease, when strong and fast control is needed. It is usually given for a limited course to bring the disease under control, then followed by a gentler maintenance medication. It is used in myositis based on specialist experience and evidence rather than a formal Canadian myositis indication.

How to take it
  • Most often given as an IV infusion at intervals (for example every few weeks), sometimes as tablets.
  • You are given plenty of fluid, anti-nausea medication, and often a bladder-protecting medicine (mesna) with IV doses.
  • It is used for a defined period, then your team switches you to a maintenance medication.
  • Follow the exact schedule and hydration instructions you are given.
What to expect
  • It acts relatively quickly to bring severe disease under control.
  • You are monitored closely with blood tests between doses.
  • Once disease is controlled, you move to a gentler long-term medication.
Benefits

How it helps you.

Controls severe disease fast

Brings serious or organ-threatening myositis under control when other options are not enough.

Effective for severe lung disease

A key option for rapidly progressive myositis-related lung involvement.

Time-limited

Used for a defined course rather than indefinitely.

A bridge to maintenance

Gains control, then hands over to a gentler long-term medication.

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
Nausea
Common around infusions, managed with anti-nausea medication.
Hair thinning
Can occur and usually recovers after the course ends.
Fatigue
Feeling tired around treatment is common.
Low blood counts
Expected and monitored; the dose and timing are set around your blood tests.
Serious but uncommon
Bladder irritation or bleeding
Can irritate the bladder. Hydration and mesna protect it. Report blood in the urine.
Higher infection risk
Blood counts drop after each dose, raising infection risk at those times.
Effects on fertility
It can affect future fertility. Options to preserve fertility are discussed before starting.
Small long-term cancer risk
Long or repeated use carries a small increased risk of bladder and blood cancers, which is why courses are limited.
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Fertility and bladder protection are planned first.

Because cyclophosphamide can affect fertility and irritate the bladder, your team discusses fertility preservation and uses hydration and a bladder-protecting medicine before and during treatment. It is used for the shortest effective course.

Staying safe

Monitoring and precautions.

Regular monitoring
  • Blood counts before and between doses, watching the low point after each dose.
  • Kidney and liver function are checked.
  • Urine tests to watch for bladder irritation.
  • Infection watch, especially when counts are at their lowest.
Daily precautions
  • Drink plenty of fluid around each dose to protect the bladder, as instructed.
  • Avoid live vaccines; flu and COVID vaccines are recommended, timed with your team.
  • Report infections early, especially in the week or two after a dose.
  • Discuss fertility preservation before starting if you may want children.
When to call your doctor

Contact the clinic if you notice:

Blood in the urine
Pink or red urine, or burning, may signal bladder irritation. Report promptly.
Fever or signs of infection
Any fever or feeling very unwell, especially after a dose. Report urgently.
Unusual bleeding or bruising
May signal low blood counts.
Severe nausea or vomiting
That is not controlled by your anti-nausea medication.
Mouth sores or sore throat
Can occur when blood counts are low. Report them.
Planning pregnancy
Discuss timing and fertility with your team well ahead.

Pregnancy & breastfeeding

Cyclophosphamide must not be used in pregnancy, since it can harm the baby, and it can affect fertility. Effective contraception is essential during treatment. If you may want children, talk with your team about fertility preservation before you start.

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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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