Abacavir hypersensitivity reaction

Associated drugs: abacavir (Ziagen), Trizivir (abacavir+AZT+3TC ), Kivexa (abacavir+3TC).

The main side effect associated with abacavir is a hypersensitivity reaction (HSR) which occurs in around 5% of people. However, a screening test (called HLA-B*5701), reduces this risk to less than 1%.

This test is recommended for all patients in the UK before using abacavir.

HSR means that the body is oversensitive to the drug. Hypersensitivity reactions can also occur with nevirapine, T-20, fosamprenavir and cotrimoxazole (Septrin). Genetic screening test are not available for these other drugs.

Hypersensitivity reaction to abacavir occurs during the first six weeks of therapy in over 90% of cases, Rarely, it can occur much later without any previous symptoms.

You need to know the symptoms of abacavir HSR before starting therapy, even if the B*5701 genetic test indicates a low risk. These include:

• Temperature
• Rash – normally raised and differing in colour from surrounding skin
• Diarrhoea and abdominal pain
• Tiredness and feeling generally unwell
• Nausea and vomiting
• Headache
• Flu-like aches and pains including muscle pain
• Cough and shortness of breath
• Sore throat

These symptoms are general and can be mistaken for many other illnesses including cold, flu and chest infections, especially during the winter period.

It is very important that if you get any of these symptoms after starting abacavir, you see your doctor straight away so that hypersensitivity can be ruled out. A few people who test negative for B*5701 may still get HSR. Even if you tested negative, if you get these symptoms, then contact your doctor.

If these symptoms get progressively worse each day it is an indication that this is HSR. A rash is not always present.

Do not stop taking your medication until you have seen a doctor and a diagnosis of hypersensitivity has been made.

If you stop using abacavir before you have seen a doctor with these symptoms then you will not be able to restart, as hypersensitivity cannot then be ruled out. This means you will be reducing your future treatment options.

If HSR is diagnosed by a doctor then abacavir will be stopped straight away. These symptoms should then disappear very quickly after abacavir is stopped.

Abacavir must never be restarted at any time if you have had the hypersensitivity reaction, as this can prove fatal.

Abacavir is one of the drugs in the combination medicines Trizivir (abacavir+AZT+3TC) and Kivexa (abacavir+3TC)