Abacavir (Ziagen®) is a nucleoside analog used in combination
therapy for HIV infection. In about 5% of patients, abacavir causes a hypersensitivity
reaction; if this occurs, the drug must be stopped and never restarted, and then the
reaction will resolve on its own. The danger is that people unfamiliar with this side
effect may not recognize it. If the drug is continued (or worse, stopped and restarted),
the reaction can worsen and cause life-threatening hypotension (low blood pressure). The
hypersensitivity reaction usually occurs within the first six weeks of treatment with
abacavir; however, it can occur at any time during therapy.
This risk of hypersensitivity to abacavir has long been known. But
recently the FDA and Glaxo Wellcome changed the warning in the official labeling to point
out that respiratory symptoms may be part of the hypersensitivity reaction. Shortness of
breath has always been in the description; now cough and sore throat have been added. This
is because some cases of hypersensitivity to abacavir were initially diagnosed as
pneumonia, bronchitis, or respiratory tract illness.
Patients using abacavir, who suspect they may have the
hypersensitivity reaction need to contact their physician immediately. If this reaction
occurs, the drug must be stopped. But the cost of stopping unnecessarily because of a
false diagnosis of hypersensitivity reaction is that an important option will be lost.
Therefore, when patients have symptoms suggestive of a hypersensitivity reaction, a
careful evaluation by the health care provider is important.
Below is the January, 2000 letter sent by Glaxo Wellcome to health
care professionals, warning them of the need to consider certain respiratory symptoms
along with other symptoms in evaluating a patient for the diagnosis of hypersensitivity to
abacavir.
Also, the complete labeling for the drug, including the new
information about the hypersensitivity reaction, is available at:
http://www.glaxowellcome.com/pi/ziagen.pdf
