Abacavir is a nucleoside analogue that is very potent against HIV. The main side effect associated with this drug is a hypersensitivity reaction (HSR) which occurs in around 5% of people.

The reaction can prove fatal. The risk increases if it is not diagnosed quickly and abacavir treatment stopped.

Hypersensitivity reaction occurs during the first six weeks of therapy in over 90% of cases, but can occur at any time during abacavir use even after over a year without previous symptoms.

The EMEA (the drug licensing authority in Europe) has issued new guidelines for the use of abacavir. These state that close medical supervision is needed during the first two months of therapy and recommends that doctors see people every two weeks during these first two months.

It is very important that people are aware of the symptoms of abacavir HSR before starting therapy. These include:

These symptoms are very 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.

If these symptoms get progressively worse each day it is an indication that they may be symptoms of a hypersensitivity reaction.

A rash is not present in all cases of HSR.

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 can’t be ruled out. This means you will be reducing your future treatment options.

If a HSR is diagnosed 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.

The overall mortality rate from hypersensitivity reaction in patients using abacavir is 0.03% – which is very small, but highlights the importance of awareness of these symptoms.

It is also reassuring that the incidence of hypersensitivity reactions has remained constant and has not increased since the drug was approved following wider use.

The mortality rate from people who have used abacavir, and then taken it again after stopping due to hypersensitivity symptoms, is 4%. This is very high – and highlights the importance of not returning to use abacavir if you have suspected HSR symptoms.

If you are restarting abacavir following an interruption in treatment then you and your doctor should observe the same cautions as if you were starting treatment for the first time.

Abacavir (Ziagen) is one of the drugs in Trizivir (abacavir/AZT/3TC in a single formulation).