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A Study About Switching From TDF to TAF

October/November 2015

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Researchers enrolled HIV-positive participants who were taking regimens containing TDF (tenofovir disoproxil fumarate), the original formulation of tenofovir. All participants had been on their current regimen for at least 96 weeks and had a viral load less than 50 copies/ml during this time. Once in the study, participants were randomly assigned to either receive a regimen containing TAF (tenofovir alafenamide), the new formulation of tenofovir, or to continue with their existing TDF-containing regimen. Researchers presented interim results analysed from 48 weeks of data (the study is planned to continue for 96 weeks). The results suggest that switching to a TAF-based regimen is generally safer than continuing to take TDF-containing regimens, particularly for bone and kidney health.


Study Details

Prior to being randomized, participants were on the following regimens, all of which contained TDF:

  • Stribild, a fixed-dose combination of  TDF + FTC + elvitegravir + cobicistat (459 people)
  • TDF + FTC + atazanavir + ritonavir  (601 people)
  • Atripla, a fixed-dose combination of TDF + FTC + efavirenz (376 people)

Participants were randomized on a 2:1 ratio to receive one of the following regimens:

  • TAF + FTC + elvitegravir + cobicistat (959 people)
  • continue their existing regimen (477 people)

The average profile of participants upon entering the study was as follows:

  • age -- 41 years
  • 89% men, 11% women
  • CD4+ cell count -- 670 cells/mm3
  • proportion who had less than 200 CD4+ cells -- less than 1%
  • proportion who had mild to moderate levels of sugar in their urine -- 9% (suggestive of kidney dysfunction)


Results

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Proportion of participants with a viral load less than 50 copies/ml at week 48:

  • TAF-based regimen -- 97%
  • TDF-based regimen -- 93%

The proportion of participants with virological failure was 1% in each of the randomized interventions.

The proportion of participants with no virological data at week 48 was as follows:

  • TAF-based regimen -- 2%
  • TDF-based regimen -- 6%


A Note About Claims of Superiority

The overall statistical analysis suggests that a TAF-based regimen is statistically superior to a TDF-based regimen. However, this statistical difference arose because more participants taking a TDF-based regimen did not have data available for analysis at week 48. This may have occurred because they dropped out of the study or were not able to be found by researchers or there may be other reasons that the data were missing. Furthermore, the regimen that TAF users received contained the integrase inhibitor elvitegravir. Integrase inhibitors are the most potent anti-HIV drugs; they quickly reduce viral load and an integrase inhibitor-based regimen would likely outperform a regimen containing a protease inhibitor (such as atazanavir) or a non-nuke (such as efavirenz). Therefore, the claim of statistical superiority may be technically correct, but it might also arise because of factors likely unrelated to the use of TAF.


Comparing Regimens

At week 48, the following proportion of participants had a viral load that was less than 50 copies/ml:

  • prior use of Atripla and then switched to a TAF-based regimen -- 96%
  • prior use of Atripla and continued on that regimen -- 90%
  • prior use of atazanavir and then switched to a TAF-based regimen -- 97%
  • prior use of atazanavir and continued on that regimen -- 92%
  • prior use of Stribild and then switched to a TAF-based regimen -- 98%
  • prior use of Stribild and continued on that regimen -- 97%


Side Effects and Complications

Overall, the proportion of participants who left the study prematurely due to side effects was as follows:

  • TAF-based regimen -- 1%
  • TDF-based regimen -- 3%

Some of these people left because of kidney-related events, as follows:

  • TAF-based regimen -- one case each of kidney failure and declining kidney function
  • TDF-based regimen -- one case of chronic kidney disease and a handful of cases of kidney injury

Other reasons that participants receiving either TAF or TDF gave for leaving prematurely seemed to be related to anxiety and depression.


General Side Effects

Here is the distribution of side effects reported by at least 5% of participants, showing marginal differences between the two formulations of tenofovir:

Diarrhea

  • TAF users -- 10%
  • TDF users -- 9%

Headache

  • TAF users -- 7%
  • TDF users -- 4%

Bone/joint pain

  • TAF users -- 6%
  • TDF users -- 5%

Problems falling asleep or staying asleep

  • TAF users -- 5%
  • TDF users -- 6%

Back pain

  • TAF users -- 5%
  • TDF users -- 5%

Nausea

  • TAF users -- 5%
  • TDF users -- 3%


Abnormal Lab Test Results

Moderate to seriously abnormal lab test results occurred in 25% to 30% of participants, depending on the medicines they were taking. As with other studies of TAF, this drug did not appear to cause more abnormal lab test results than TDF.

The most common abnormal blood test results that were moderate to serious in severity were distributed as follows:

Elevations in the enzyme creatine kinase (possibly suggestive of muscle injury)

  • TAF users -- 10%
  • TDF users -- 10%

Elevations in the liver enzyme AST (suggestive of liver injury)

  • TAF users -- 5%
  • TDF users -- 7%

Elevations in the liver enzyme ALT (suggestive of liver injury)

  • TAF users -- 5%
  • TDF users -- 5%

Less-than-normal levels of neutrophils (these cells are part of the immune system)

  • TAF users -- 4%
  • TDF users -- 3%

Less-than-normal levels of phosphate (suggestive of kidney injury)

  • TAF users -- 2%
  • TDF users -- 3%
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Tenofovir Alafenamide (TAF) Still Noninferior to Current Tenofovir -- With Better Bone/Kidney Signals



This article was provided by Canadian AIDS Treatment Information Exchange. It is a part of the publication TreatmentUpdate. Visit CATIE's Web site to find out more about their activities, publications and services.
 


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