A few months ago, Bristol-Myers Squibb released data from a study of the interaction of Viread (tenofovir) with Videx EC (enteric-coated ddI). The results were also recently presented at the XIV International AIDS Conference. Viread needs to be taken with food once a day for optimal blood levels, while Videx EC needs to be taken on an empty stomach once a day. Since it was known that Viread caused some increase in blood levels of ddI, it was hoped that by taking Viread and Videx EC together, with food, adequate levels of both drugs would be achieved with once-daily dosing.
Unfortunately the drug interaction of Viread with Videx EC is greater than expected. So the concern is that whether the two drugs are taken together or apart, the blood levels of ddI may be too high. The levels of ddI increased from 48 to 64 percent, both when Videx and Viread were taken together and when they were taken 2 hours apart. (This study was performed on a small number of HIV-negative people. Multiple studies have shown that drugs levels in HIV-positive people can be very different than in HIV-negative people for completely unknown reasons.) Because ddI may cause inflammation of the pancreas (pancreatitis), which can be fatal even after the drug is stopped (although this is rare), this interaction is of significant concern.
Bristol-Myers Squibb has sent a letter to all healthcare providers informing them of this interaction and advising them to monitor their patients closely. But is this enough? Unfortunately, the next lower dose of ddI available, at 250 mg, is the old formulation, which is not as well tolerated as Videx EC. Also, that formulation is not approved for once-daily dosing as the Videx EC formulation is, and the same drug interaction study with Viread has not been conducted. [Note from The Body's editor: According to the prescribing information, Videx EC is available in a 250 mg dose and can be taken once-daily.] Adding to this challenge, many people on the combination of Viread and Videx EC are on that combination because of resistance to other agents, so they have limited options for discontinuing or switching to other drugs.
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