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 is sometimes given in combination with another medicine called tretinoin.

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

You should not be treated with arsenic trioxide if you are allergic to it.

Tell your doctor if you have ever had:

• heart problems, or a heart rhythm disorder;
• long QT syndrome (in you or a family member);
• an electrolyte imbalance (such as low levels of potassium or magnesium in your blood);
• kidney disease; or
• liver disease.

Arsenic trioxide can harm an unborn baby if the mother or the father is using this medicine.

• If you are a woman, do not use arsenic trioxide if you are pregnant. Use effective birth control to prevent pregnancy while you are using this medicine and for at least 6 months after your last dose.
• If you are a man, use effective birth control if your sex partner is able to get pregnant. Keep using birth control for at least 3 months after your last dose.
• Tell your doctor right away if a pregnancy occurs while either the mother or the father is using arsenic trioxide.

It may be harder for you to get a woman pregnant while you are using this medicine. You should still use birth control to prevent pregnancy because the medicine can harm an unborn baby.

Do not breastfeed while using this medicine, and for at least 2 weeks after your last dose.

Use Arsenic Trioxide (Trisenox) exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Arsenic trioxide can cause a condition called differentiation syndrome, which affects blood cells and can be fatal if not treated. This condition may occur within 1 days to 2 months after you start taking this medicine.

Seek medical help right away if you have symptoms of differentiation syndrome:

• fever, cough, trouble breathing;
• dizziness;
• rash;
• decreased urination;
• rapid weight gain; or
• swelling in your arms or legs.

Also call your doctor right away if you have:

• fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness (like you might pass out);
• confusion, decreased consciousness;
• problems with vision, balance, or muscle movement;
• a seizure;
• fever, tiredness, night sweats;
• easy bruising or bleeding;
• high blood sugar--increased thirst, increased urination, dry mouth, fruity breath odor;
• low magnesium--dizziness, irregular heartbeats, feeling jittery, muscle cramps, muscle spasms, cough or choking feeling; or
• low potassium--leg cramps, constipation, irregular heartbeats, fluttering in your chest, increased thirst or urination, numbness or tingling, muscle weakness or limp feeling.

Common side effects may include:

• stomach pain, nausea, vomiting, diarrhea;
• cough, sore throat, trouble breathing;
• fever, chills, tiredness, headache, joint pain;
• fast or irregular heartbeats;
• numbness or tingly feeling;
• low magnesium or potassium, high blood sugar;
• itching, rash;
• swelling;
• joint or muscle pain; or
• trouble sleeping.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Follow your doctor's instructions about any restrictions on food, beverages, or activity.