An investigational drug is one that is under study and is not approved by the U.S. Food and Drug Administration (FDA) for sale in the United States. Medical research studies are conducted to evaluate the safety and effectiveness of an investigational drug. These research studies are also called clinical trials. Once an investigational drug has been proven safe and effective in clinical trials, FDA may approve the drug for sale in the United States.
Tenofovir alafenamide is an investigational drug that is being studied for the treatment of HIV infection. It is also being studied for the treatment of chronic hepatitis B in people who are not infected with HIV.4
Tenofovir alafenamide belongs to a class (group) of HIV drugs called nucleoside reverse transcriptase inhibitors (NRTIs).2 NRTIs block an HIV enzyme called reverse transcriptase. (An enzyme is a protein that starts or increases the speed of a chemical reaction.) By blocking reverse transcriptase, NRTIs prevent HIV from multiplying and can reduce the amount of HIV in the body.
Tenofovir alafenamide is a prodrug, which means that it is an inactive drug. Once taken, a prodrug does not work until the body converts it into an active form. In the body, tenofovir alafenamide is converted to tenofovir diphosphate (TFV-DP).5
Studies suggest that tenofovir alafenamide may be more effective against HIV and cause fewer side effects than the FDA-approved NRTI tenofovir disoproxil fumarate (brand name: Viread).6
Tenofovir alafenamide is currently being studied as a component of two investigational fixed-dose combination (FDC) drugs for the treatment of HIV infection. (Fixed-dose combination drugs include two or more drugs in a single dosage form, such as a capsule or tablet.) Tenofovir alafenamide is being studied in the following combinations:
o elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide7
o darunavir/cobicistat/emtricitabine/tenofovir alafenamide3
Clinical trials are conducted in phases. Each phase has a different purpose and helps researchers answer different questions.8
In most cases, an investigational drug must be proven safe and effective in a Phase III clinical trial to be considered for approval by the FDA for sale in the United States. Some drugs go through the FDA’s accelerated approval process and are approved before a Phase III clinical trial is complete. After a drug is approved by the FDA and made available to the public, researchers track its safety in Phase IV trials to seek more information about the drug’s risks, benefits, and optimal use.8
Tenofovir alafenamide, as part of two different fixed-dose combination tablets, is currently being studied in Phase II and Phase III clinical trials.2,3
In a 10-day, early-phase study, three different doses of tenofovir alafenamide taken once daily were compared to placebo and to tenofovir disoproxil fumarate (given at the standard dose) in HIV-infected participants. (A placebo is an inactive drug that is identical in appearance to the active drug being studied.) Some participants had never taken HIV medicines before entering the study (treatment-naive), and others had taken HIV medicines previously (treatment-experienced). Study participants did not receive additional HIV medicines as part of a background regimen. (A background regimen is a combination of drugs that are not being studied as the investigational drug[s] in the clinical trial, but are being given to help control a participant’s HIV infection.)6,9
In this study, tenofovir alafenamide at the two higher doses studied (25 mg and 40 mg) proved more effective than tenofovir disoproxil fumarate at lowering viral load (the amount of HIV in the blood). Tenofovir alafenamide also resulted in higher TFV-DP levels inside cells and lower tenofovir concentrations in the blood than tenofovir disoproxil fumarate did. In terms of safety, there were no reports of significant laboratory abnormalities or serious side effects related to tenofovir alafenamide use.6
Additional Phase II and III trials involving tenofovir alafenamide as part of fixed-dose combination tablets are under way in treatment-naive adults.3,7
In the 10-day, early-phase study discussed under the previous question, no serious side effects occurred.6
In a Phase II study of a fixed-dose combination tablet containing tenofovir alafenamide, the following side effects were reported after 24 weeks of treatment: nausea, diarrhea, fatigue, headache, and infection of the upper airway (such as the common cold).10
Because tenofovir alafenamide is still being studied, information on possible side effects of the drug is not complete. As testing of tenofovir alafenamide continues, additional information on possible side effects will be gathered.
More information about tenofovir alafenamide-related research studies is available from the AIDSinfo database of ClinicalTrials.gov study summaries. Click on the title of any trial in the list to see the ClinicalTrials.gov trial summary and more information about the study.
Participating in a clinical trial can provide benefits. For example, a volunteer participant can benefit from new research treatments before they are widely available. Participants also receive regular and careful medical attention from a research team that includes doctors and other health professionals. However, clinical trials may also involve risks of varying degrees, such as unpleasant, serious, or even life-threatening side effects from the treatment being studied.8
Your health care provider can help you decide whether participating in a clinical trial is right for you. For more information, visit NIH Clinical Research Trials and You.
1. United States National Library of Medicine. ChemIDplus Advanced.
2. National Institute of Allergy and Infectious Diseases (NIAID). NIAID ChemDB, HIV Drugs in Development.
3. Gilead Sciences. A Phase 2, Randomized, Double-Blinded Study of the Safety and Efficacy of Darunavir/Cobicistat/Emtricitabine/GS-7340 Single Tablet Regimen Versus Cobicistat-boosted Darunavir Plus Emtricitabine/Tenofovir Disoproxil Fumarate Fixed Dose Combination in HIV-1 Infected, Antiretroviral Treatment Naive Adults. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on March 27, 2012. NLM Identifier: NCT01565850. Last accessed April 12, 2013.
4. Gilead Sciences. A Phase 1b Randomized, Open Label, Active-Controlled Study to Assess the Safety, Viral Kinetics, and Anti-HBV Activity of GS-7340 in Treatment-Naive Adults With Chronic Hepatitis B (CHB) Infection. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on August 21, 2012. NLM Identifier: NCT01671787. Last accessed April 12, 2013.
5. García-Lerma JG, Aung W, Cong ME, et al. Natural substrate concentrations can modulate the prophylactic efficacy of nucleotide HIV reverse transcriptase inhibitors. J Virol. 2011 Jul;85(13):6610-7.
6. Ruane P, DeJesus E, Berger D, et al. GS-7340 25 mg and 40 mg Demonstrate Superior Efficacy to Tenofovir 300 mg in a 10-day Monotherapy Study of HIV-1+ Patients. Paper presented at: 19th Conference on Retroviruses and Opportunistic Infections (CROI); March 5-8, 2012; Seattle, WA. Paper 103.
7. Gilead Sciences. A Phase 3, Randomized, Double-Blind Study to Evaluate the Safety and Efficacy of Elvitegravir/Cobicistat/Emtricitabine/Tenofovir Alafenamide Versus Elvitegravir/Cobicistat/Emtricitabine/ Tenofovir Disoproxil Fumarate in HIV-1 Positive, Antiretroviral Treatment-Naïve Adults. In: ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). Registered on January 16, 2013. NLM Identifier: NCT01780506. Last accessed April 12, 2013.
8. National Institutes of Health (NIH). NIH Clinical Research Trials and You.
9. Mascolini M. Low-Dose, Cell-Homing Tenofovir Prodrug Outdoes TDF in 10-Day Study. Conference Reports for National AIDS Treatment Advocacy Project (NATAP): 19th Conference on Retroviruses and Opportunistic Infections (CROI); March 5-8, 2012; Seattle, WA. Accessed April 22, 2013.
10. Zolopa A, Ortiz R, Sax P, et al. Comparative Study of Tenofovir Alafenamide vs Tenofovir Disoproxil Fumarate, Each with Elvitegravir, Cobicistat, and Emtricitabine, for HIV Treatment. Paper presented at: 20th Conference on Retroviruses and Opportunistic Infections (CROI); March 3-6, 2013; Atlanta, GA. Paper 99LB.
Last Reviewed: May 29, 2013
Last Updated: May 29, 2013