Glaxo-Wellcome US has issued a warning about the potential for severe hypersensitivity reactions after abacavir reintroduction in patients who have no identified history or unrecognised symptoms of hypersensitivity to abacavir therapy.
The warning follows a number of reports where the company believes that hypersensitivity was not spotted prior to an interruption in abacavir therapy. For example, hypersensitivity could have been mistaken for an acute respiratory illness, a gastrointestinal infection or a reaction to other medicines.
However, some individuals discontinued abacavir due to interruptions in drug supply or the need to treat other illnesses, and suffered severe hypersensitivity reactions when abacavir treatment was resumed. This may have occurred because abacavir hypersensitivity reactions can take a number of weeks to emerge, and if treatment stops in the early weeks, the clock isn't re-set; a severe reaction can resume within hours if the drug is reintroduced.
Although the symptoms vary, they tend to involve fever, rash, nausea, vomiting, diarrhoea, abdominal pain, lethargy and malaise. Less common symptoms include shortness of breath or difficulty breathing, cough, sore throat, muscle or joint pain, headache, numbness on the skin, puffiness of the throat, face and neck, swollen glands, conjunctivitis, mouth ulcers and low blood pressure.
Typically, a pattern of symptoms build up over a period of days, often worsening as successive doses are taken. Death has occurred when respiratory symptoms due to a hypersensitivity reaction were mistaken for a respiratory infection.
The abacavir hypersensitivity reaction is most commonly seen in the first six weeks of taking the drug, often in the initial fortnight.
European drug regulators have not asked Glaxo-Wellcome to issue a similar warning in Europe at this time.
The full text of the letter is available at the FDA's Medwatch site