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An Overview of Racivir

January 9, 2017

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The study of PSI-5004 has been discontinued. See page 3 in this document for details:

As of January 9, 2017, this record is no longer being maintained.

Other Names: (+)/(-)-FTC, PSI-5004, RCV
Drug Class: Nucleoside Reverse Transcriptase Inhibitors
Molecular Formula: C8 H10 F N3 O3 S
Registry Number: 143491-54-7 (CAS)
Chemical Name: 4-amino-5-fluoro-1-[(2S,5R)-2-(hydroxymethyl)-1,3-oxathiolan-5-yl]pyrimidin-2-one
Chemical Class: Pyrimidine Nucleosides
Company: Pharmasset, Inc.
Phase of Development: Phase II
Molecular Weight: 247.249
(Compound details obtained from ChemIDplus Advanced1, NIAID Therapeutics Database2, and Antiviral Chemistry & Chemotherapy journal article3)

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.

What is racivir?

Racivir is an investigational drug that is being studied for the treatment of HIV infection.

Racivir 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.

Racivir is similar in chemical structure to the FDA-approved NRTIs lamivudine (brand name: Epivir) and emtricitabine (brand name: Emtriva).4

In vitro studies have shown that racivir is also active against hepatitis B virus (HBV).4 (In vitro studies are studies done in test tubes or other laboratory equipment and not on animals or humans.)

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.5

  • 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.5

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.5

In what phase of testing is racivir?

Racivir has been studied in Phase II clinical trials.2

What have recent studies shown about racivir?

In a Phase II study, racivir was compared to lamivudine in HIV-infected participants who were already taking HIV medicines before entering the study (treatment-experienced) and who had the M184V HIV mutation (a mutation associated with drug resistance to the HIV medicine lamivudine). Before starting the study, all participants were on a failing antiretroviral therapy (ART) regimen that included lamivudine. (A failing ART regimen is one that is not effective at controlling a person's HIV.) Study participants were randomly assigned to receive either racivir in place of lamivudine or to continue with lamivudine as part of their ART.6,7

In this study, racivir was shown to decrease viral load (the amount of HIV in the blood) in the treatment-experienced adults who had the M184V resistance mutation and who had fewer than three thymidine analog mutations (HIV mutations associated with NRTI drug resistance). In terms of safety, no severe drug-related side effects occurred in either the racivir treatment group or the lamivudine treatment group.7

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This article was provided by AIDSinfo. Visit the AIDSinfo website to find out more about their activities and publications.

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