Video originally created by FDA -- posted by Lawsuit.com on March 10, 2009

FDA is cautioning healthcare professionals against using skin patch testing to immunologically confirm suspected cases of hypersensitivity reaction in patients treated with the antiretroviral drug abacavir. Abacavir is sold under the trade name Ziagen and is part of the combination products Epzicom and Trizivir.

Abacavir is associated with serious and potentially fatal hypersensitivity reactions. Patients with a particular HLA allele, HLA-B*5701, have a higher risk of developing these reactions if they are treated with abacavir, and so abacavir is not recommended for these patients. Because of this, a boxed warning recommends that all patients be screened for the HLA-B*5701 allele before starting or restarting abacavir therapy. If a hypersensitivity reaction is suspected in any patient, even those without the allele, the drug should be stopped immediately and permanently, because rechallenging the patient with abacavir could be fatal.

Abacavir hypersensitivity reactions can be difficult to diagnose because they can be confused with adverse events from the patient’s other HIV medications, or they may mimic the infections that frequently occur in HIV patients.

Several research reports have described using skin patch testing to confirm suspected cases of abacavir hypersensitivity immunologically. However, data suggest that skin patch testing may miss cases of true hypersensitivity reaction or provide false positive results. FDA points out that the accuracy of skin patch testing is unknown, and that using skin patch testing to confirm cases of abacavir hypersensitivity has not been validated clinically. Given that rechallenging a patient with a suspected hypersensitivity reaction could be fatal, these reactions must continue to be diagnosed clinically.