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Abacavir and Tenofovir
Apr 24, 2004

Hallo!I'm italian and Iread your suggestions about medicins association.Why, don't you recommend abacavir+tenofovir commercil name in Italy Ziagen and Viread? Thanks

Response from Dr. Sherer

Because these two drugs together, in combination with lamivudine, in several trials have performed miserably in treatment naive patients.

In the largest study, the ES30009, which intended to compare this regimen to an EFV + ABC + 3TC-containing regimen, one half of the patients on ABC + TDF + 3TC failed. The study was halted due to the dismal performance of this arm. And half of those failures had multi-class resistance, i.e. resistance to TDF and 3TC, or to both ABC and 3TC.

Virologic analyses of this and other studies of this regimen show surprisingly weak antiviral activity of the regimen, on the order of a one log decline in viral load, which is far weaker than either tenofovir or abacavir alone.

It is not clear why this regimen did so badly. There do not appear to be predictable drug interactions between the two drugs, though this has not been studied exhaustively. Resistance alone does not appear to account for the high degree of failure, i.e. baseline resistance assays did not detect high levels of resistance to any of the 3 drugs in the regminen. More study is needed to answer this important question.

These results should lead clinicians and patients alike to be VERY CONSERVATIVE when it comes to choosing a first line regimen. There are several excellent, simple, well-tolerated options in this era. One should choose from them and avoid the temptation to experiment with new combinations until they have been shown to be effective in clinical trials. It seems this lesson is learned over and over in HIV medicine.

So, the recommendation is very strong that the combination of 3TC and TDF and ABC should NEVER be used in naive patients.

In my own practice, I have conducted a review of ALL patients on both TDF and ABC in light of this information to look for any evidence of unexpectedly poor performance. This of course includes many patients who are heavily treatment experienced, and its often difficult to discern a single reason for regimen failure.

returning to a previous resistant drug.

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