Potential side effects and toxicity: Hypersensitivity reaction (HSR, an allergic-like reaction). Approximately 5% of people (1 in 20) taking abacavir experienced HSR during clinical trials. People who think they are experiencing HSR must be evaluated by an experienced HIV provider as soon as possible before they stop taking abacavir. Be very careful, especially in the first two months of treatment. Symptoms worsen with every dose, but very slowly. If treatment is stopped by the medical provider because of this serious reaction, they can never take abacavir, Epzicom or Trizivir again (called “re-challenging”) because of life-threatening and potentially fatal reaction. (This does not apply to missed doses, when there’s no HSR, but watch for symptoms if you’ve stopped the drug for at least a few days). This reaction usually occurs during the second week of treatment, but may take as long as six weeks to appear, gets progressively worse and resolves quickly (24–48 hours) after permanent discontinuation. Symptoms usually, but not always, include some combination of sudden fever, muscle ache, severe nausea, vomiting or abdominal pain, severe tiredness, respiratory symptoms (cough, difficulty breathing and sore throat) and possibly mild rash. These symptoms are listed on the patient information sheet and warning card that you receive each time you fill your Ziagen prescription. You should always keep the warning card with you. HSR might be confused with flu during flu season, but remember that it worsens with every dose. See Epzicom tips.
More common side effects include nausea, vomiting, diarrhea, fatigue, headache, fever, rash, anorexia (loss of appetite), and potentially high blood sugar and high triglyceride levels (fat in the blood). Rare but potentially fatal toxicity with all NRTIs is pancreatitis (inflammation of the pancreas), hepatomegaly (enlarged liver) with steatosis and lactic acidosis (accumulation of lactate in the blood and abnormal acid-base balance). Lactic acidosis has been seen in patients taking NRTIs but is more severe in women, especially those overweight; and more common in people with liver disease, but can occur in people without a history of liver damage. Symptoms include persistent fatigue, abdominal pain or distension, nausea/vomiting, and difficulty breathing or shortness of breath; and enlarged, fatty liver (called hepatomegaly with steatosis). Pancreatitis can be life-threatening and may cause pain in the stomach and back, along with nausea, vomiting and blood in the urine. Check for pancreatitis by checking for increased levels of amylase and lipase in the blood. Risks for pancreatitis include: higher than recommended doses of NRTIs, advanced HIV, and alcohol use. Children should be monitored carefully for pancreatitis.
Potential drug interactions: Excessive alcohol increases abacavir levels and might increase its side effects. People with moderate to severe cirrhosis should use abacavir with caution. No clinically significant interactions between abacavir and other drugs have been observed.
Tips: Studies show that abacavir crosses the blood-brain barrier to a useful degree, which may be beneficial for patients at risk for neurological damage (such as dementia) from HIV. The pattern of viral resistance to abacavir is similar to that of other NRTIs, though abacavir can retain some activity when other NRTI’s have lost most activity.
The manufacturer recommends that people with symptoms of acute respiratory disease consider hypersensitivity even if other diagnosis such as pneumonia, bronchitis or flu is possible, but this is undoubtedly a legal issue. Be careful before you unnecessarily drop Ziagen, and burn through a potent and tolerable HIV drug. Check with your doctor if you have any side effects after taking this medicine—don’t just stop! Doctors report seeing a higher incidence of HSR in people taking abacavir as part of their first drug regimen (Studies done comparing side effects were with this group.). An analysis of 8,000 patients found a reduced risk of HSR in blacks and in men.
Doctor
Abacavir (ABC) is a potent nucleoside analog (the only guanosine analog in the arsenal). In 2004 it received FDA approval for use once-daily allowing for greater flexibility and convenience. It is now available in three forms: Ziagen, or one of two fixed-dose-combination tablets (Trizivir and Epzicom). Another advantage to this agent is it has a somewhat higher threshold for acquiring resistance than 3TC. The biggest potential drawback is a hypersensitivity reaction (allergy) which in rare circumstances may be fatal. In studies, this allergy occurs in 5-9% of the population and if it happens, the drug must be stopped immediately and never restarted. There is no way to test for or predict this reaction and unfortunately, concern by providers has somewhat limited an otherwise excellent drug from wider use.—Chad J. Zawitz, MD
Activist
Another very effective nucleoside analog that has shown to be key to many backbones for NNRTIs and PIs. But it can cause a hypersensitivity reaction that can be lethal if not dealt with quickly. If you feel like you are coming down with the flu a few days after starting the drug, call your doctor immediately. This problem occurs in less than 10% of people. Ziagen is now gaining a lot more momentum after several studies showed that it may not cause lipoatrophy. I have my own biases about this drug, however. I experienced increased anxiety while on it. I am glad that a few reports came up in the literature about this problem after that, but it is something that has not been studied at all and that is ignored by doctors due to lack of information. Ziagen is available alone or in a combo with Epivir (Epzicom) or in a 3-drug combo with AZT and Epivir (Trizivir). Warning: Trizivir alone may not be effective to treat HIV in most patients. Also, do not take Epzicom plus Viread, since you may fail this regimen too quickly and develop resistance to most nucleosides.—Nelson Vergel
|
