Arsenic trioxide is a cancer medication. Arsenic trioxide interferes with the growth of cancer cells and slows their growth and spread in the body.

Arsenic trioxide is used to treat a cancer of the blood and bone marrow called acute promyelocytic (pro-MYE-loe-SIT-ik) leukemia, or APL.

Arsenic trioxide may also be used for other purposes not listed in this medication guide.

Call your doctor at once if you have a serious side effect such as sharp chest pain, wheezing, rapid breathing, feeling short of breath, dry cough, feeling weak or tired, dizziness, fainting, fast or pounding heartbeat, fever, or swelling in your ankles or feet.

Do not use arsenic trioxide without telling your doctor if you are pregnant. It could harm the unborn baby. Use effective birth control, and tell your doctor if you become pregnant during treatment.

Before receiving arsenic trioxide, tell your doctor if you have congestive heart failure, a heart rhythm disorder, an electrolyte imbalance, high blood pressure, a history of "Long QT syndrome," liver disease, or kidney disease.

There are many other drugs that can interact with arsenic trioxide. Tell your doctor about all your prescription and over-the-counter medications, vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start a new medication without telling your doctor.

To be sure this medication is helping your condition and not causing harmful effects, your blood will need to be tested on a regular basis. You must remain under the care of a doctor while you are using arsenic trioxide. Do not miss any follow-up appointments.

You should not use this medication if you are allergic to arsenic trioxide.

If you have any of these other conditions, you may need a dose adjustment or special tests to safely use this medication:

• congestive heart failure;

• a heart rhythm disorder or history of "Long QT syndrome";

• an electrolyte imbalance (such as low levels of potassium or magnesium in your blood);

• high blood pressure;

• liver disease; or

• kidney disease.

FDA pregnancy category D. Arsenic trioxide can cause harm to an unborn baby or cause birth defects. Before you receive this medication, tell your doctor if you are pregnant. Use an effective form of birth control, and tell your doctor if you become pregnant during treatment.

Arsenic trioxide can pass into breast milk and may harm a nursing baby. Do not use this medication without telling your doctor if you are breast-feeding a baby.