Potential side effects and toxicity: The most common side effects of Epzicom are the same as Epivir and Ziagen. See those pages for more information.

Potential drug interactions: See also Epivir and Ziagen for more information. Do not take Epivir or Ziagen while taking Epzicom since these medications are already in Epzicom. The hypersensitivity reaction (HSR, an allergic-like reaction) warning on abacavir (Ziagen) bears repeating here. Approximately 5% of people (1 in 20) taking abacavir experienced hypersensitivity during clinical trials. People who think they are experiencing hypersensitivity must be evaluated by an experienced HIV provider as soon as possible before they stop taking abacavir. If treatment is stopped because of this serious reaction, they can never take abacavir or Trizivir or Epzicom again (called “re-challenging”) because of life-threatening and in a few instances fatal reaction. (This does not apply to missed doses, when there’s no HSR.) This hypersensitivity 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 prescription. You should always keep the warning card with you. Hypersensitivity might be confused with flu during flu season, but remember that HSR worsens with every dose. See tips.

Tips: Remember, Epzicom is two drugs in one pill, so see the pages for those drugs, Epivir and Ziagen. Ziagen by itself is FDA approved for either once-a-day or twice-a-day dosing. The once-daily formula in Epzicom was found to have the same amount in the blood over 24 hours (bioequivalency) as Ziagen twice-a-day. The race is on: Epzicom, or Truvada? Both are a combination of two drugs taken as one pill, once a day. (This is called FDC, for “fixed-dose combination.”) Both were approved by the FDA on the same day last August. All four drugs have already been out in the drug store. Moreover, two of the four drugs (Epivir and Emtriva) are virtually identical (except that Emtriva lasts longer in the blood; however, in head-to-head data, Emtriva did not do as well as Epivir 150 mg twice a day). Perhaps the quick and dirty way to divide the two is by toxicity: the drugs in Truvada are fairly tolerable (see Emtriva and Viread), however, more and more patients are complaining of abdominal distension due to excessive gas production and bloating. The Ziagen in Epzicom unfortunately has a hypersensitivity reaction (HSR) in anywhere from 5–8% of people taking it. The incidence of HSR was the same between Epzicom and Ziagen twice-a-day (8% vs. 9%), but the incidence of severe reactions was higher with Epzicom (5% vs. 2%). Remember that the HSR cited may have been suspected, not definitely diagnosed. Doctors say they see more HSR in people who are taking HIV meds for the first time. (Studies done comparing side effects were with this group.) Check with your doctor if you have any side effects after taking this medicine—don’t just stop!

On the other hand, the toxicity and drug interactions with the Viread in Truvada are still being worked out. (See Viread for some of the problems that have arisen.)
Then there’s resistance. K65R is the primary mutation for both Viread and Ziagen, so, you probably can’t go from Epzicom to Truvada and expect to see huge improvement if your virus has come back while on Epzicom. And what about Truvada’s longer lasting blood levels? Some doctors think that makes it a better choice, other doctors think otherwise, as that has yet to be determined. Many medical providers will say that the effect of half-life and of many of the resistance mutations—including K65R—have not been clinically proven. In other words, what does it do for your health? Experienced doctors, however, will avoid prescribing either FDC for people with the mutations at codon 103 on their resistance test.
How about Combivir vs. Epzicom? Glaxo has compared Combivir to Epzicom in a 48-week study, with comparable side effects.