Cytoxan (Cyclophosphamide) is a medication that works by suppressing the immune system. It is an important treatment option for serious autoimmune diseases.

Cytoxan may be used to treat several different types of rheumatic disease including Systemic Lupus Erythematosus (SLE), diseases that inflame the walls of blood vessels (forms of vasculitis), and sometimes for Rheumatoid Arthritis.

Cytoxan is best known for its other use as a chemotherapy drug that is used to treat certain types of cancers.

Taking Cytoxan

Cytoxan is available in two forms: 50mg tablets, and intravenous infusion.

Cytoxan – Administration, Dose, and Frequency

Cytoxan tablets are taken once a day while intravenous infusions are given every 2-4 weeks.

The dose of Cytoxan is based on body weight.

The usual starting dose for tablets is 1.5 to 3 of them, at 50 mg each, per day, for a total daily dose of 75 to 150 mg.

The dose of intravenous Cytoxan usually ranges from 500 to 1500 mg per infusion, with the exact dose decided by the prescribing doctor.

It takes 6 to 12 weeks for the Cytoxan to start working. It is important for patients starting this medicine to keep taking it as prescribed.

Taking Cytoxan tablets with food can help reduce stomach upset.

Important Tests and Risks

Regular Blood and Urine Tests

Patients taking Cytoxan should have their blood and urine tested regularly (usually every two weeks to every month) to make sure that the medicine isn’t affecting blood counts or harming the bladder. Patients that are receiving Cytoxan by intravenous infusion should get a personal schedule for blood tests from their doctor.

Drink Lots of Water

Patients taking Cytoxan are advised to drink lots of water (8 to 10 glasses per day) to help reduce the risk of side effects to the bladder.

Risk of Infection

Cytoxan can make it a bit harder for people to fight off infections.

Patients taking this medicine should call their doctor they have a fever, think they have an infection, or have been prescribed antibiotics to treat an infection.

Patients should coordinate with their doctor to stop treatment before any surgery. It can be re-started once things have healed and there’s no sign of infection.

Patients should discuss all vaccinations with their doctor because some are not advisable to get while taking Cytoxan.

Not Safe in Pregnancy

Cytoxan can harm an unborn child. Patients who might have sex and could get pregnant should use reliable birth control.


How Cytoxan Works

Cytoxan (Cyclophosphamide) is an alkylating agent that prevents a variety of different types of cells from dividing, or making copies of themselves.

Alkylating agents like Cytoxan work by attaching themselves to parts of DNA inside cells. This interferes with the DNA’s ability to replicate and in turn prevents cells from dividing. The cells may die, and when they do, there are no younger copies to replace them.

Cytoxan’s effect is useful for treating some types of cancers where tumor cells are dividing out of control.

Cytoxan is also very good at preventing some types of immune system cells (white blood) cells from dividing and this effect is what makes it useful for treating rheumatic diseases.

In patients with rheumatic disease, the immune system is attacking the body by mistake. Cytoxan softens this attack by preventing immune system cells from replicating and making more of themselves.

Although suppressing the immune system can make it harder for patients to fight off infections, it also helps to stabilize the immune system if it is overactive.


Side Effects

Cytoxan is a powerful medicine that requires regular blood and urine tests to monitor for more serious side effects.

MORE COMMON side-effects include:

  • Nausea, vomiting, abdominal pain, and diarrhea
  • Sores in the mouth
  • Skin rashes

RARE side-effects include:

  • Hair Loss – Some patients lose their hair when taking Cytoxan. This is more common with higher doses and grows back when stopped.
  • Blood Counts – Cytoxan can cause a drop in the numbers of red blood cells (which carry oxygen), white blood cells (which are needed to fight infection), and platelets (which help to stop bleeding). The blood counts are monitored closely and changes are usually reversible when the medication is discontinued.
  • Infection – Any infections or fevers should be taken seriously and reviewed by a doctor.
  • Bladder – Cytoxan can irritate the bladder which may cause pain and bleeding. To reduce the risk of this happening it is important to drink 8 to 10 glasses of water per day. Patients who notice blood in their urine should tell their doctor immediately.
  • Fertility – Cytoxan can affect fertility in both men and women. The effect may be reversible when the medication is stopped. Patients who might be planning pregnancy in the future should discuss this very carefully with their doctor.
  • Malignancy – When used for long periods of time, Cytoxan may be associated with a small increased risk of lymphoma, bladder, and skin cancer.

How to minimize the side-effects of Cytoxan:

  • Patients should take Cytoxan as prescribed and get regular blood and urine tests
  • Patients should attend all doctor appointments
  • Drink 8 to 10 glasses of water per day to reduce the risk of bladder irritation
  • Take any antibiotics that may be prescribed along with Cytoxan

Patients should talk to their doctor if they are concerned about any side effects.

To stop Cytoxan, patients are usually weaned down slowly. Rheumatic diseases can “flare” after this medication is stopped, especially if it is stopped suddenly.

Cytoxan may cause birth defects and result in miscarriage. Patients must avoid pregnancy and breastfeeding while taking this medicine, and are advised to use reliable birth control.

Who Should NOT Take Cytoxan

Patients who should NOT be taking Cytoxan include:

  • Patients who have had a previous reaction to Cytoxan
  • Women who are pregnant, planning on becoming pregnant, or are breast feeding
  • Men who are planning pregnancy with their partner
  • Some patients with diseases of the liver, kidney, or blood disorders
  • Patients with active infections
  • Possibly patients with a past history of cancer

Patients who become pregnant while taking Cytoxan should notify their doctor immediately.

When to Call a Doctor

Patients should call their doctor if they feel sick and want to stop, or they are concerned about any side effects.

Other reasons to call a doctor while taking Cytoxan include:

  • Nausea or Diarrhea
  • Fever or possible infection
  • Becoming pregnant or planning pregnancy
  • Blood in the urine or pain with urination
  • Before any surgery


Watch Dr. Andy Thompson, a Canadian rheumatologist, introduce Cytoxan in this short video: