Predicting Abacavir Hypersensitivity

Question: Predicting Abacavir Hypersensitivity

Answer: While we can't be 100% certain who will and who won't have hypersensitivity to Abacavir, there is now genetic screening via a simple blood test that helps identify those patients who are at an increased risk. For a majority of people, Abacavir is a very safe drug, causing few or no side effects at all. About 8% of those who take the drug, though, will have a hypersensitivity reaction, although the aforementioned percentage varies in different populations. The reaction can be very serious. In fact, there have been recorded deaths attributed to Abacavir hypersensitivity reactions. The reaction typically occurs between two and six weeks after starting Abacavir therapy, but has been known to emerge after six weeks or longer. Symptoms of Abacavir sensitivity include:

• fever(80% of patients with hypersensitivity)
• rash (60% to 70%)
• headache/feeling bad/no energy (60%)
• nausea, vomiting, diarrhea or stomach pain (50%)
• cough, shortness of breath or sore throat (20%)

Important Note!
Hypersensitivity not only occurs with Abacavir alone, but with combination drugs containing Abacavir, namely Trizivir and Epzicom. Therefore, the potential for hypersensitivity exists for those drugs as well.

There's Now a Blood Test that Identifies Those at Risk

Recent work in the field of genetics has resulted in a new and simple blood test that can tell doctors who may be at an increased risk for Abacavir hypersensitivity reaction. Genetic screening via a simple blood test reveals a person's HLA types. The HLA screening looks for the HLA-B*5701 allele, which identifies those patients at risk for a hypersensitivity reaction. A positive HLA-B*5701 means the patients exhibit the HLA-B*5701 gene. People with this gene have an increased risk of Abacavir hypersensitivity. The Food and Drug Administration (FDA) is now recommending patients have the HLA-B*5701 blood test prior to starting any regimen containing Abacavir. If the test comes back positive, the patient should not be given any regimen containing Abacavir and should have the drug added to his or her list of allergies.

If you doctor tells you he or she would like to start you on any regimen containing Abacavir, insist that your doctor order the HLA-B*5701 before taking any doses of Abacavir or Abacavir containing medications.

_{Source
The New Mexico AIDS Infonet; Fact Sheet #416 - Abacavir (Ziagen); aidsinfonet.org; 23 Aug 2008.}