A Study About Switching From TDF to TAF
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.
Prior to being randomized, participants were on the following regimens, all of which contained TDF:
Participants were randomized on a 2:1 ratio to receive one of the following regimens:
The average profile of participants upon entering the study was as follows:
Proportion of participants with a viral load less than 50 copies/ml at week 48:
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:
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.
At week 48, the following proportion of participants had a viral load that was less than 50 copies/ml:
Side Effects and Complications
Overall, the proportion of participants who left the study prematurely due to side effects was as follows:
Some of these people left because of kidney-related events, as follows:
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:
Problems falling asleep or staying asleep
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)
Elevations in the liver enzyme AST (suggestive of liver injury)
Elevations in the liver enzyme ALT (suggestive of liver injury)
Less-than-normal levels of neutrophils (these cells are part of the immune system)
Less-than-normal levels of phosphate (suggestive of kidney injury)
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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