Trizivir can cause serious, life-threatening side effects. These include allergic reactions, a buildup of lactic acid in the blood (lactic acidosis), liver problems, muscle pain or weakness (myopathy), and blood disorders such as extremely reduced numbers of red blood cells (severe anemia) or reduced numbers of white blood cells (neutropenia). Trizivir contains abacavir, an HIV medicine. People who take abacavir-containing products may have a serious allergic reaction (hypersensitivity reaction) that can cause death. Your risk of this allergic reaction is much higher if you have a gene variation called HLA-B*5701. Your health care provider can determine if you have this gene variation with a blood test. If you get a symptom from two or more of the following groups while taking Trizivir, contact your health care provider right away to find out if you should stop taking Trizivir.