Abacavir is a medication used in combination with other drugs to treat human immunodeficiency virus (HIV) infection. It is a nucleoside reverse transcriptase inhibitor (NRTI) that helps manage HIV by interfering with the virus’s replication process. While generally effective, abacavir carries a risk of a serious immune system reaction known as abacavir hypersensitivity, which can affect multiple organ systems.
Understanding Abacavir Hypersensitivity
Abacavir hypersensitivity is an immune reaction distinct from typical allergic responses. This reaction is strongly linked to a person’s genetic makeup, particularly the presence of the human leukocyte antigen B5701 (HLA-B5701) allele. Individuals with this genetic variant have an immune system that mistakenly identifies abacavir as a harmful substance.
The mechanism involves abacavir binding to the HLA-B5701 molecule. This binding alters the shape of the HLA-B5701 molecule, causing it to present different self-peptides to the immune system’s T cells. These altered self-peptides are then recognized as foreign, triggering an inflammatory response.
Signs and Symptoms
Signs and symptoms of abacavir hypersensitivity typically appear within the first six weeks of treatment, with a median onset around 8 to 11 days. Recognizing these symptoms is important, as they can worsen with continued use and involve multiple organ systems.
A common initial sign is fever. Rashes are also frequently observed, often appearing as maculopapular or diffuse. Gastrointestinal symptoms like nausea, vomiting, diarrhea, and abdominal pain are frequently reported.
Patients may also experience respiratory symptoms such as cough, shortness of breath, or a sore throat. General malaise, including fatigue, aches, and headaches, can also be present. If symptoms from two or more of these categories appear, it is recommended to discontinue abacavir and seek medical attention.
Prevention Through Genetic Testing
The primary preventative measure for abacavir hypersensitivity is mandatory genetic screening for the HLA-B5701 allele before starting abacavir therapy. This screening involves a simple blood test that checks for the presence of this specific genetic material. The test helps identify individuals who are at a significantly elevated risk of developing the reaction.
Individuals who test positive for the HLA-B5701 allele should never be prescribed abacavir due to their extremely high risk of developing hypersensitivity. Implementing this genetic testing has significantly reduced the incidence of abacavir hypersensitivity reactions.
Management and What to Do
If abacavir hypersensitivity is suspected, immediate and permanent discontinuation of abacavir is necessary. Delaying discontinuation can lead to a more severe and potentially life-threatening reaction. Symptoms usually resolve within 72 hours of stopping the medication.
Re-exposure to abacavir after a hypersensitivity reaction is extremely dangerous. It can cause a rapid, severe, and potentially fatal recurrence of symptoms, often within hours. This recurrence is typically more severe than the initial reaction and can include life-threatening hypotension. Therefore, abacavir or any medication containing it must never be restarted in such patients. Alternative HIV medications are available to ensure continued effective treatment.