Arsenic trioxide belongs to a category of drugs called as anti-neoplastics. It acts by causing changes in the DNA of abnormal cells, thus causing cell death and preventing the spread of cancer.

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.

 Nausea,
 Vomiting,
 Increased heart rate,
 Rash,
 Decreased potassium level in blood,
 Paresthesia (tingling or pricking sensation),
 Breathlessness,
 Dizziness,
 Injection site pain,
 Increased liver enzymes,
 Increased glucose level in blood,
 Fever,
 Diarrhea,
 Fatigue,
 Itching

You may be monitored with ECG before and after starting the treatment.
Use an effective method of birth control to avoid pregnancy while taking this
medication.
You may need regular blood tests to monitor the levels of calcium, potassium, and
creatinine in the blood.