Unusual abacavir hypersensitivity reaction involving severe respiratory symptoms reported

An unusual case of abacavir (Ziagen) hypersensitivity reaction affecting the lungs is reported in the January 9^th edition of AIDS.

It is thought that between 3 and 8% of individuals starting abacavir develop a severe, and potentially life-threatening, allergic reaction to the drug. Hypersensitivity to the drug usually occurs within the first six weeks of its treatment, and the most frequently reported symptoms are fever, rash, nausea, vomiting, diarrhoea and abdominal pain.

Less often, individuals who experience a reaction to abacavir develop symptoms affecting the lungs such as shortness of breath, cough and sore throat. When these symptoms do occur, they tend to be mild.

A genetic test can be used to predict whether a patient is likely to experience a hypersensitivity reaction after starting abacavir. Patients who do not have the HLA-B*5701 gene have a very low probability of experiencing this side-effect, however, the test is not widely used.

Doctors from New York report the case of a 57 year-old man who developed a hypersensitivity reaction to abacavir involving severe respiratory symptoms. The man was diagnosed with HIV in 2002 and originally treated with an antiretroviral regimen consisting of efavirenz (Sustiva) and Combivir (AZT and 3TC). Because of a fall in his CD4 cell count, this was changed after three months to a regimen comprising Kaletra (lopinavir/ritonavir) with abacavir and AZT.

Six days after starting treatment with abacavir the man complained of extreme tiredness, diarrhoea and chills and fevers. These symptoms worsened over the next two days and he was admitted to hospital. There was no evidence of cough or shortness of breath at this time and his chest X-ray was clear.

However, within three days of his admission to hospital the man developed severe shortness of breath, had low oxygen levels in his blood, was coughing blood, and a chest X-ray indicated inflammation of the lungs.

Suspecting a hypersensitivity reaction, treatment with abacavir was immediately stopped and the patient was placed on a ventilator. Tests, including a bronchoscopy, were performed to rule out an infectious cause for the patient’s pulmonary difficulties. These were all negative. Within three days of treatment with abacavir being discontinued, the man was taken off the ventilator and a chest X-ray showed that inflammation in his lungs had largely resolved.

“The hypersensitivity reaction described here highlights the potential aggressive respiratory manifestations associated with the use of abacavir”, write the investigators, adding that the case “is remarkable because of the unusual presentation of acute respiratory distress syndrome as the manifestation of hypersensitivity reaction to abacavir.”

Early detection of abacavir hypersensitivity is essential, the investigators emphasise. They conclude, “given the possibility of severe lung involvement, clinicians need to monitor their patients on abacavir closely and understand the need for the rapid discontinuation of the drug, as this is the only established treatment, if symptoms arise.”