Arsenic trioxide is a strong medication that can cause serious, rarely fatal side effects. To decrease your risk, your doctor will monitor you closely during treatment.

Infrequently, this medication may cause a serious condition called APL differentiation syndrome. Tell your doctor immediately if the following effects occur: unusual/unexplained fever, shortness of breath/difficulty breathing, and/or weight gain. Your doctor may direct you to weigh yourself regularly and report any sudden weight gain. Your doctor may also perform certain exams or tests (e.g., lung exam, X-rays) to determine if this syndrome has developed.

Infrequently, this medication can also cause serious (rarely fatal) heart problems (e.g., AV block, torsades de pointes-type arrhythmias). Tell your doctor if you have any medical history of heart problems (e.g., fast/irregular heartbeat, heart failure), kidney problems, low levels of minerals in your blood (e.g., calcium, potassium, magnesium). Also tell your doctor if you take any medications that increase your risk for these heart problems or low levels of minerals (see also Drug Interactions section). To decrease your risk, your doctor may order a heart rhythm test (EKG) or blood tests before and during treatment.

Seek immediate medical attention if you develop severe dizziness, fainting, or fast/irregular heartbeat.