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Hypersensitivity (allergic) reactions

The anti-HIV drugs with the greatest risk of hypersensitivity, or allergy, are abacavir (Ziagen, also in the combination pills Kivexa and Trizivir) and nevirapine (Viramune).

Atazanavir (Reyataz), etravirine (Intelence), efavirenz (Sustiva, also in Atripla), darunavir (Prezista), fosamprenavir (Telzir), maraviroc (Celsentri) and raltegravir (Isentress) may also cause an allergic reaction.

Abacavir hypersensitivity

Abacavir can cause a serious hypersensitivity (allergic) reaction. This is associated with the presence of a particular gene called HLA-B*5701. Before starting treatment with abacavir (or any treatment that contains abacavir) you should first have a blood test to see if you have this gene. If the test is positive you must not take abacavir. If the test is negative, it is highly unlikely that an allergic reaction will occur, but contact your HIV clinic immediately (or A&E if out of hours) if you begin to feel unwell after starting the drug.

In the box with the drug there is an ‘alert card’, which you should carry with you for the first six weeks of taking abacavir. The particular side-effects you should look out for during this time are:

  • Any skin rash OR
  • If you get one or more symptoms from at least TWO of the following groups:

Group 1: fever

Group 2: shortness of breath or sore throat or cough

Group 3: nausea or vomiting or diarrhoea or abdominal pain

Group 4: severe tiredness or achiness or generally feeling ill.

You should never retry abacavir, or take Trizivir or Kivexa, if you have had an allergic reaction to abacavir previously.

Nevirapine liver toxicity

A small number of people who start treatment with nevirapine (Viramune) develop serious liver problems. This can cause very serious skin rashes (including Stevens Johnson syndrome or toxic epidermal necrolysis). Symptoms can include:

  • fever
  • generally feeling ill
  • extreme tiredness
  • muscle or joint aches
  • blisters
  • oral lesions
  • eye inflammation
  • facial swelling
  • signs and symptoms of liver problems (e.g., yellowing of your skin or whites of your eyes, dark or tea-coloured urine, pale-coloured stools/bowel movements, nausea, vomiting, loss of appetite, or pain, aching or sensitivity on your right side below your ribs).

If you develop these symptoms whilst taking this drug, you should contact your HIV clinic immediately (or A&E if out of hours).

Your liver function will be monitored closely during the first 18 weeks you are on nevirapine.

To reduce the risk of an allergic reaction to nevirapine, you should not start treatment with nevirapine if you have a detectable viral load and, for men, a CD4 cell count above 400 or, for women, a CD4 cell count of more than 250.

If you have an allergic reaction of this type to nevirapine, you should not take it again in the future.

Other hypersensitivity reactions

A very rare hypersensitivity (allergic) reaction has been reported in some people using other anti-HIV drugs, including atazanavir, etravirine, efavirenz, darunavir, fosamprenavir, maraviroc and raltegravir. This can cause a severe rash, called Stevens Johnson syndrome. See your HIV clinic immediately (or A&E if out of hours) if you develop a rash together with any of these symptoms:

  • fever
  • feeling generally unwell or extremely tired
  • muscle or joint ache
  • blistering of the skin
  • mouth ulcers
  • swelling of the eye, lips, mouth or face
  • breathing difficulties
  • yellowing of the skin or eyes
  • dark urine
  • pale stools
  • pain, aching or sensitivity on the right-hand side of the body, below the ribs.

If you have this sort of reaction, you should not take the drug which caused it again in the future.

It’s possible that other drugs, including other anti-HIV drugs, might rarely cause allergic reactions too. It is therefore important that you tell your doctor as soon as possible if you develop a rash, fever, or feel generally unwell soon after starting treatment with a new drug.


Published July 2013

Last reviewed July 2013

Next review July 2016

Contact NAM to find out more about the scientific research and information used to produce this booklet.

This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.
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We can end HIV soon if people have equal access to HIV drugs as treatment and as PrEP, and have free choice over whether to take them.

Launched today, the Community Consensus Statement is a basic set of principles aimed at making sure that happens.

The Community Consensus Statement is a joint initiative of AVAC, EATG, MSMGF, GNP+, HIV i-Base, the International HIV/AIDS Alliance, ITPC and NAM/aidsmap