Abacavir (trade name Ziagen) is a newly approved anti-HIV drug in the same class as AZT. The class is called nucleoside analogs, or NRTIs, and includes AZT, ddI, ddC, d4T and 3TC. Study results suggest that abacavir may have the strongest anti-HIV effect of the NRTI drugs. Researchers are still studying abacavir in combination with other anti-HIV drugs and the best way of using abacavir is not yet clear.

Taking the drug: The recommended dose of abacavir is one 300 mg pill taken twice a day. Abacavir can be taken with or without food.

Recent Public Health Service HIV treatment guidelines say that the best way to use anti-HIV drugs is in combinations. The guidelines recommend combinations of three or four anti-HIV drugs as first treatment for HIV. The guidelines haven't yet been updated to include information on abacavir.

The company that makes abacavir, 3TC and AZT (Glaxo-Wellcome) is suggesting that the combination of abacavir, 3TC and AZT may be a good first HIV treatment. One important study of abacavir/AZT/3TC as first treatment is ongoing. This study is comparing abacavir/AZT/3TC to a standard combination of Crixivan/AZT/3TC. Information is only available after six months, and so far both combinations have had about the same effect on T4 cell counts and viral load. However, it's too early to tell if abacavir/AZT/3TC will continue to work as well as currently recommended combinations. A recent study found that abacavir/AZT/3TC did not work very well in people with viral loads over 100,000 copies. There is also very little information on the long term side effects of three NRTI drugs taken together.

Other studies have suggested that abacavir may be strong enough to use instead of two NRTI drugs (e.g. AZT/3TC) in standard treatment combinations. In a small, yearlong study of the two-drug combination of abacavir and Agenerase (an experimental protease inhibitor), most study participants had their viral loads reduced to levels too low for the test to measure.

For people that have already taken NRTI anti-HIV drugs, abacavir may not always work so well due to drug resistance. The changes in HIV that cause drug resistance are called mutations, and different mutations cause resistance to different drugs. In clinical trials, if a person's HIV already had three or more mutations that made it resistant to other NRTI drugs, abacavir did not have anti-HIV effect.

Side effect warning! Hypersensitivity (allergic) reactions to abacavir have been reported in approximately 3-5% of people in the clinical trials. Symptoms began an average of 11 days after starting the drug. Symptoms were a general sick feeling, low grade fever and nausea, with or without vomiting. There can also be symptoms that affect breathing, such as shortness of breath, cough and sore throat. In some people, a rash appeared 1-3 days after onset of these symptoms. All symptoms resolved within 1-2 days after stopping treatment. If treatment was started again at reduced doses, potentially fatal symptoms developed within hours.

Several study participants who tried to restart abacavir after having a hypersensitivity reaction had to be hospitalized, and two people died. Study participants are now being told to report any flu-like symptoms with or without rash beginning several days to 4 weeks after starting treatment, and to stop treatment immediately if symptoms occur. Treatment with abacavir should not be restarted.

Side effect update, July 2000: Some people have experienced potentially fatal symptoms after restarting abacavir even though they did not stop the drug due to a hypersensitivity reaction. In these reports, people interrupted treatment with abacavir for other reasons and were not having problems with abacavir when they stopped. When they restarted the drug, they developed the same severe life-threatening symptoms as those seen in people who stopped due to an allergic reaction. Several people are thought to have died as a result. Restarting abacavir after an interruption should be done with extreme caution and only when emergency medical care is easily accessible.

The other side effects that have been seen so far with abacavir include increased fatigue, changes in liver function tests, headache, abdominal pain, constipation, diarrhea, nausea, vomiting, sleeplessness, skin rash, and dizziness.

Allergic Reaction Registry: A special toll-free number has been set up for reporting cases of hyper-sensitivity (allergy) to abacavir. The number to call is (800) 270-0425.

A new warning letter about fatal hypersensitivity re-actions to abacavir can be dowloaded from the Internet at: http://www.fda.gov/medwatch/safety/2000/safety00.htm#ziagen

The manufacturers of abacavir have set up a patient assistance program for people having problems affording or accessing the drug. Call (800) 722-9294 for more information.

The Simple Facts Project is a program of the AIDS Treatment Data Network (The Network). This information does not intend to promote or endorse any specific treatment for any health related condition.