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TMC 114/125 Resistance Already?
Apr 27, 2006

hello dr-

i have been in the Tibotec DUET study (TMC 114/125) since January. I was responding well VL went from 250,000 to 25,000 and t-cells from 6 to 26. now my april labs show a VL of 47,000 and t-cells of 15. i am on on ABR of Fuzeon and Truvada-- could this be evidence of resistance already? or might it be a blip in the numbers. is 25,000 that much different form 47,000? any help is appreciated.

thanks!

Response from Dr. Sherer

Thank you for this email - your case shows the importance of patience, and of asking the right questions.

First of all, as you suggest, your initial viral load showed a very good initial response to your new regimen, i.e. a one log decline in viral load.

Secondly, since you had a viral load of 250,000 when you started the regimen in January, I would not be surprised for you to need 4-6 months for your viral load to decline to below detection. This is more common in patients with low CD4 cells and high baseline viral loads.

Next, the answer to the question "Is there much difference between a viral load of 25,000 and a viral load of 47,000" is no. For one viral load to be significantly different than another, a difference of 3-fold or more is required. So these viral loads are the same. And, as above, since it might be expected that you would need 4-6 months to achieve a viral load below detection, e.g. below 50 copies, that is still possible.

I should also point out that in the clinical trials in which TMC-114 was tested, only about one-third of patients did achieve that threshold, i.e. viral load below 50 copies/ml. The percent improved above 1/3 in patients who were also started at the same time on T-20 (Fuzeon), which you are also on, though I don't know if you had received this drug before. And the percent also increased if the other drugs in the regimen had activity, which is likely to be the case with your regimen, given the known activity of the other drug in the regimen, i.e. TMC 125, the new non-nucleoside that is active against virus that is resistant to most current NNRTIs (like evafirenz = Sustiva).

So you have a good chance of achieving full suppression, but also a chance of not getting there.

So how to interpret your last values? They are not worse...and they are not better. You and your doctor might have preferred to see the second value with another 1 log decline, i.e. to 2,500 or less, but that did not happen.

Also, the CD4 cell count is not a significant difference from the earlier value, i.e. 26 to 15 is not a significant change. And it's also not better.

As I said at the start, I advise patience, awaiting your next values, and discussing the results, your questions, and these comments with your doctor.

Finally - could this be resistance already? Yes, it could be, if there is prolonged viremia in the presence of this regimen. If, however, this is part of a prolonged decline from 250,000 to zero, and this is just a random value along the way, resistance to the members of this regimen is less likely.

If resistance is occurring, it is likely to be occurring to the more vulnerable drug in the regimen, eg TMC 125. Also, your doctor may be more able to answer this question specifically based on his or her knowledge of your past treatment history and resistance test results.


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