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An Overview of Tenofovir Alafenamide

May 29, 2013

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Other Names: GS-7340, TAF, prodrug of tenofovir, tenofovir alafenamide fumarate
Drug Class: Nucleoside Reverse Transcriptase Inhibitors
Molecular Formula: C21 H29 N6 O5 P
Registry Number: 379270-37-8 (CAS)
Chemical Name: isopropyl (2S)-2-[[[(1R)-2-(6-aminopurin-9-yl)-1-methyl-ethoxy]methyl-phenoxy-phosphoryl]amino]propanoate
Chemical Class: Purine Nucleotides
Company: Gilead Sciences
Phase of Development: Phase II and III (as part of fixed-dose combination [FDC] tablets; one FDC tablet is in Phase II testing, and another one is in Phase III testing)
Molecular Weight: 476.4711
(Compound details obtained from ChemIDplus Advanced1, NIAID Therapeutics Database2, and ClinicalTrials.gov3)


What is an investigational drug?

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.


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What is tenofovir alafenamide?

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:

  • elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide7
  • darunavir/cobicistat/emtricitabine/tenofovir alafenamide3

How are clinical trials of investigational drugs conducted?

Clinical trials are conducted in "phases." Each phase has a different purpose and helps researchers answer different questions.8

  • Phase I trials: Researchers test an investigational drug in a small group of people (20-80) for the first time. The purpose is to evaluate its safety and identify side effects.
  • Phase II trials: The investigational drug is administered to a larger group of people (100-300) to determine its effectiveness and to further evaluate its safety.
  • Phase III trials: The investigational drug is administered to large groups of people (1,000-3,000) to confirm its effectiveness, monitor side effects, compare it with standard or equivalent treatments, and collect information that will allow the investigational drug to be used safely.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

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This article was provided by AIDSinfo. Visit the AIDSinfo website to find out more about their activities and publications.
 
See Also
More on HIV Medications
More on NRTIs in Development

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