Cyclophosphamide (Cytoxan): Uses, Side Effects and Protecting Your Bladder

By the Oncol.net editorial team · Last updated November 1, 2026

Cyclophosphamide (Cytoxan) is a chemotherapy drug used for breast cancer, lymphomas, leukemias, multiple myeloma and other cancers. It can inflame and bleed the bladder, so drink or receive plenty of fluid around each dose and empty your bladder often. Blood counts usually hit their low point in weeks 1 and 2 and return to normal after about 20 days. Call right away for pink or red urine, or a temperature of 100.4°F (38°C) or higher.

What cyclophosphamide is and how it works

Cyclophosphamide is one of the oldest and most widely used chemotherapy drugs. It has been approved in the US since 1959. It is an alkylating drug, which means it damages DNA. The exact mechanism is not fully worked out, but its active forms appear to link DNA strands together so that fast-growing cancer cells cannot keep dividing.

The drug does nothing until your body activates it. Enzymes in the liver convert it to its working forms. This is why severe liver disease can make it less effective.

Cytoxan is the brand name many people know. Most patients receive generic cyclophosphamide. It is the same medicine.

What cyclophosphamide treats

The label covers a long list of cancers in adults and children. It is usually combined with other drugs.

Breast cancer
Lymphomas, including Hodgkin lymphoma and non-Hodgkin types such as Burkitt lymphoma
Multiple myeloma
Leukemias, including CLL, CML, AML and ALL
Ovarian cancer
Neuroblastoma and retinoblastoma, which are childhood cancers
Mycosis fungoides, a lymphoma of the skin

Common combinations listed by the National Cancer Institute include:

Regimen	Drugs	Main use
AC	Doxorubicin, cyclophosphamide	Breast cancer
CMF	Cyclophosphamide, methotrexate, fluorouracil	Breast cancer
CHOP	Cyclophosphamide, doxorubicin, vincristine, prednisone	Non-Hodgkin lymphoma
R-CHOP	CHOP plus rituximab	B-cell non-Hodgkin lymphoma, including diffuse large B-cell lymphoma

Doctors also use cyclophosphamide outside cancer care and in preparation for bone marrow transplant. Those uses have different doses and risks, so the numbers on this page may not apply.

How cyclophosphamide is given

It is given into a vein, or taken by mouth at home.

By IV. When it is the only cancer drug, the label describes these schedules. They show what a patient may see. They are not advice for your dose.

Schedule	Typical amount
First course	40 to 50 mg per kg of body weight, divided over 2 to 5 days
Every 7 to 10 days	10 to 15 mg per kg
Twice a week	3 to 5 mg per kg

In combination regimens, the dose and cycle length follow that regimen, and the dose may be lower. The infusion should run slowly. Running it too fast can cause facial swelling, headache, a stuffy nose and a burning scalp. Tell your nurse if you notice these. Some products contain alcohol, which may affect your ability to drive right after the infusion. Ask whether yours does.

By mouth. MedlinePlus describes capsules taken once a day in the morning, at about the same time. Swallow them whole. Do not open, chew or crush them. If a capsule is broken or leaking, wear gloves, avoid breathing the powder and rinse any skin contact with water right away.

Before each dose your team checks your blood counts. The label says not to give the drug to patients with neutrophils at or below 1,500/mm³ and platelets below 50,000/mm³.

Protecting your bladder: hemorrhagic cystitis and hydration

Hemorrhagic cystitis means bleeding and inflammation of the bladder lining. It is the side effect most specific to cyclophosphamide. It can happen with short or long courses. Simple steps reduce how often it happens and how bad it gets. It needs attention because severe cases can be dangerous.

What helps, according to the label and MedlinePlus:

Fluids. Drink or receive plenty of fluid during and right after each dose, so that you pass more urine.
Morning dosing. The label says to give the drug in the morning, so that fluids and urination can follow during the day.
Frequent urination. Empty your bladder often. Do not hold it.
Mesna. This protective medicine has been used to prevent severe bladder damage. Your team decides whether you need it.

The label does not set one fluid target for everyone. Ask your team how much to drink, especially if you have heart or kidney problems. Too much water can also be a problem, as explained under low sodium below.

Your risk is higher if you have had radiation to the area. The drug must not be used if something is blocking your urine flow, and your team will treat or rule out a blockage first. It is used with caution, if at all, during an active urinary tract infection. Your urine may be tested regularly for blood.

This matters beyond comfort. Bladder damage can scar and shrink the bladder, and in severe cases the bladder may need to be removed. Preventing hemorrhagic cystitis may also lower the later risk of bladder cancer.

Call your care team right away for pink or red urine, blood in your urine, or urination that is frequent, urgent or painful. Do not wait for your next appointment. If you cannot pass urine at all, or are passing clots, go to the emergency room.

Side effects and when they happen

The most common side effects are low neutrophils, fever with low neutrophils, hair loss, nausea, vomiting and diarrhea.

Side effect	Timing and detail
Nausea and vomiting	Common around treatment. Your team will prescribe anti-nausea medicine. Take it as directed.
Low white cells and platelets	Nadir, the lowest point, usually comes in weeks 1 and 2. Counts are expected to return to normal after about 20 days.
Hair loss	Common. NCI says hair often regrows 2 to 3 months after chemotherapy ends. See hair regrowth after chemo.
Mouth sores, appetite loss, diarrhea	Tell your team if they are severe or do not go away.
Skin and nail color changes	Listed as common by MedlinePlus.
Slow wound healing	Tell your team before any surgery or dental work.
Effects on periods and fertility	Can start during treatment. See the fertility section below.

Your counts can drop further if you have had other chemotherapy or radiation. Your team may add a growth factor such as pegfilgrastim to lower the risk of neutropenia complications. Read about blood counts and your infection risk.

Serious warnings and when to call

Infection. Weakened immunity can lead to serious and sometimes fatal infections, including sepsis, a body-wide reaction to infection. Old infections can also come back.
Heart problems. Inflammation of the heart, fluid around the heart, irregular heartbeat and heart failure have been reported, and can be fatal. The risk is higher with high doses, older age, earlier chest radiation or other drugs that affect the heart.
Lung problems. Pneumonitis (lung inflammation) and scarring can occur, sometimes more than 6 months or even years after treatment. Report new shortness of breath or a dry cough, even long after treatment ends.
Liver blood vessel blockage. Veno-occlusive disease can be fatal. It is mainly linked to high-dose treatment before a transplant.
Low sodium. Excess body water and low sodium, sometimes called water intoxication, have been reported and can be fatal. Report confusion, severe headache or seizures.
Second cancers. Cancers of the urinary tract, leukemias, lymphomas, thyroid cancer and sarcomas have been reported after cyclophosphamide regimens. Keep up with follow-up visits after treatment ends.
Severe allergic reactions. Anaphylaxis, including deaths, has been reported.

Call your care team now if you have: a temperature of 100.4°F (38°C) or higher, or shaking chills; blood in your urine; chest pain, a racing or irregular heartbeat or new leg swelling; shortness of breath; yellow skin or eyes; unusual bleeding or bruising; or vomiting that keeps you from drinking. Call 911 for severe trouble breathing, swelling of the face or throat, fainting or a seizure. The CDC calls fever during chemotherapy a medical emergency. See when to call your doctor.

Interactions and precautions

Many medicines add to the risks of cyclophosphamide. Review all of yours with your oncology team, including non-cancer drugs.

Medicine or treatment	Possible effect
Anesthesia with succinylcholine and similar muscle relaxants	Breathing can stay stopped for longer. Tell your anesthesiologist if you had cyclophosphamide within 10 days of surgery.
Doxorubicin and related drugs, cytarabine, pentostatin, trastuzumab, chest radiation	More risk of heart damage
Amiodarone, G-CSF growth factors	More risk of lung damage
ACE inhibitors (a blood pressure group), thiazide water pills, zidovudine, natalizumab, paclitaxel	Lower blood counts or weaker immunity
Amphotericin B, indomethacin	Kidney problems. Water intoxication has been reported with indomethacin.
HIV protease inhibitors	More infections, low neutrophils and mouth sores
Azathioprine, busulfan	More liver injury; more veno-occlusive disease and mouth sores with busulfan
Warfarin	Its effect may rise or fall. Expect closer checks.
Cyclosporine	Lower cyclosporine levels
Metronidazole	Brain toxicity reported in one patient
Tamoxifen	Tamoxifen with chemotherapy may raise the risk of blood clots

If you have kidney disease, you will be monitored closely, because the drug can build up. If you are on dialysis, your team will time treatment around it. If you are not sure about a vaccine, ask your team first.

Pregnancy, breastfeeding and fertility

Cyclophosphamide can cause birth defects, miscarriage, poor fetal growth and harm to a newborn. You may need a pregnancy test before you start.

Women who could become pregnant: use effective birth control during treatment and for up to 1 year after it ends.
Men with partners who could become pregnant: use effective birth control during treatment and for 4 months after it ends.
Breastfeeding: do not breastfeed during treatment or for 1 week after the last dose, according to MedlinePlus.

Fertility risk is real and depends on the dose, how long you are treated and your age. In women, periods may stop, and in some they do not return. The label notes that eggs at any stage of development can be damaged, and that girls and young women who keep their ovarian function have a higher risk of early menopause. In men, sperm counts can fall or sperm can disappear. This can reverse, but it may take several years, and in some people infertility is permanent.

If children matter to you, ask to see a fertility specialist before your first dose, even if treatment needs to start soon. You should still use birth control during treatment, because you may be able to get pregnant or cause a pregnancy even if your periods change.

Frequently asked questions

How can I prevent bladder problems on cyclophosphamide?

Drink or receive plenty of fluid during and right after each dose, take the dose in the morning, and empty your bladder often. Some people also receive mesna, a medicine that protects the bladder. Ask your team how much to drink, and call right away if you see pink or red urine.

How much water should I drink on cyclophosphamide?

The label does not set a single amount. It says fluids should be taken in or infused in amounts large enough to increase urine flow. Your team will give you a target based on your dose, your heart and your kidneys. Follow their number, because too much water can also cause harm in some people.

When is the nadir with cyclophosphamide?

The label says white cells and platelets usually reach their lowest point in weeks 1 and 2 of treatment, and that blood counts are expected to return to normal after about 20 days. Other drugs in your regimen can change this, so ask your team when to expect your low point.

Will I lose my hair on cyclophosphamide?

Hair loss is one of the most common side effects, and other drugs in your regimen can add to it. The National Cancer Institute says hair often regrows 2 to 3 months after chemotherapy ends. It may feel different at first.

Is cyclophosphamide a strong chemo?

It depends on the dose and what it is combined with. The risk of heart damage rises with high doses, and liver blood vessel blockage is mainly linked to high-dose treatment before a transplant. Your oncologist can explain how your dose fits in.

Will cyclophosphamide stop my periods?

It can. Periods may become irregular or stop during treatment, and in some people they do not return. The chance depends on your age, dose and length of treatment. Cyclophosphamide can cause permanent infertility, so talk with your team about fertility options before you start.

Can I have surgery or anesthesia after cyclophosphamide?

Tell your surgeon and anesthesiologist if you have had cyclophosphamide within the last 10 days. It can prolong the effect of some muscle relaxants used in anesthesia, including succinylcholine. It can also slow wound healing, so your teams will plan the timing together.

Sources

This page is general information, not medical advice. Your care team knows your situation and should guide your decisions.