July 10, 2002
These are the final 48-week results of Study 907, which have been presented in prior meetings based on preliminary analyses. The optimal role for tenofovir is still evolving, but this study helps to ensure that there is confidence in one of the uses of this agent.
This study was done in patients with a viral load detectable between 400 and 10,000 copies despite their current regimen. This was a placebo-controlled trial for 24 weeks, adding tenofovir or placebo to a current partially suppressive regimen.
After 24 weeks, the placebo arm had a crossover to tenofovir. The average viral load of the 550 people enrolled was about 2,300 copies, with a CD4+ count of about 430. They had about five years of prior antiretroviral treatment, with about 60 percent on PI-based regimens and 40 percent on NNRTI regimens. Almost all had evidence of resistance to NRTIs, the family of drugs relevant to the potency of tenofovir.
These results confirm earlier presentations, showing about a 0.6 log average decline that was maintained for the entire 48-week period. The placebo arm, when crossed to drug, also had a similar decline. This translated into about 44 percent of patients going below 400 copies and 21 percent going below 50 copies; these numbers were maintained for the next 48 weeks. There was some difference in the viral load decline based on resistance profile.
The presenters commented that there was generally better suppression with less resistance, while there is less decline from a pattern that can be seen from prior AZT and d4T use, where the mutation at position 210 and 215 occur. Tenofovir also continues to have an excellent safety profile, with very minor increases in creatinine noted in less than 3 percent up to one year. There was also a small decline in the serum phosphorus levels in no more than 7 percent, a finding without clear significance.
These results continue to document that tenofovir can be used to "intensify" a regimen that is not fully suppressive. It also documents that tenofovir is an active agent in patients with prior NRTI resistance, so that it can be used in a new combination, as more than just a single drug change. The observation that tenofovir shows durable suppression to even 48 weeks is evidence that there is a high "genetic barrier" to resistance, making this drug an important one to consider in multiple circumstances.
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