Answered by:
Stuart D. Federman, PharmD, AAHIVP
Gateway Apothecary
Saint Louis, MO


The current available form of tenofovir is known as tenofovir disoproxil fumarate (TDF). It was approved by the Food and Drug Administration (FDA) in the treatment of HIV and can be taken on its own (known as Viread) or in combination drugs (such as Atripla, Complera, Stribild or Truvada).

TDF does not easily enter the body’s white blood cells meaning you have to take a higher dose to make sure the drug works. The problem with taking a high dose of TDF is that it may cause side effects, such as kidney problems or a decrease in bone density. It is important to note that studies have shown TDF does not cause an increase in the chances of having a bone break.

The new kind of tenofovir being developed is known as tenofovir alafenamide fumarate (TAF). It is currently in Phase III trials. That means TAF is being given to a large group of people to make sure it is safe and effective. TAF is being studied as a replacement for TDF in the combo drugs.

The studies show that the replacement of TDF with TAF causes less kidney problems, as well as less loss of bone density. If you have experienced kidney problems with TDF in the past, you may be able to use TAF as part of your HIV treatment. Patients who are resistant to TDF may not necessarily be resistant to TAF. Since there is a higher concentration of TAF that gets into the cells, it may bypass the current resistance mutations the virus has for TDF. More research is needed to find out the possible mutations with TAF.

TAF is different from TDF in that is more easily absorbed into the body’s white blood cells meaning you can take a lower dose. The benefit of taking a lower dose of tenofovir is a lower risk of having side effects. The lower doses of TAF have been shown to be just as, if not more, effective than TDF. Other advantages of TAF include a smaller tablet, since there is less drug that has to be taken.

TAF is an important development in HIV drugs because patients with HIV are living longer. There is a need for drugs that are effective in treating HIV, but that can be used long-term with fewer side effects.

Additional writing Jeremy Samuels, Pharm. D candidate 2015.