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AIDSinfo Drug Database

AIDSinfo Drug Database

Drugs by class



Racivir  Audio icon

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
Chemical Image:
Click image to enlarge
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

What side effects might racivir cause?

In a 14-day Phase Ib/IIa study of various doses of racivir, the most common side effects reported were mild to moderate dizziness and headache, both of which may have been related to racivir. Some other side effects that occurred in the study and may have been because of racivir included the following: difficulty concentrating, nausea, fatigue, common cold, and eye discomfort. Heartburn and vomiting were also noted by participants and may have been associated with racivir.8

In the Phase II study discussed under the previous question, no severe side effects were reported after 28 days of treatment with racivir.7

Because racivir is still being studied, information on possible side effects of the drug is not complete. As testing of racivir continues, additional information on possible side effects will be gathered.

Where can I get more information about clinical trials studying racivir?

More information about racivir-related research studies is available from the AIDSinfo database of study summaries. Click on the title of any trial in the list to see the trial summary and more information about the study.

I am interested in participating in a clinical trial of racivir. How can I find more information about participating in a clinical trial?

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.5

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. Hurwitz SJ, Otto MJ, Schinazi RF. Comparative pharmacokinetics of Racivir, (+/-)-beta-2',3'-dideoxy-5-fluoro-3'-thiacytidine in rats, rabbits, dogs, monkeys and HIV-infected humans. Antivir Chem Chemother. 2005;16(2):117-27.

4. Sen S, Mathur AG, Gupta RM, Kapila K, Chopra GS. Investigational antiretroviral drugs. Recent Pat Antiinfect Drug Discov. 2008 Nov;3(3):199-205.

5. National Institutes of Health (NIH). NIH Clinical Research Trials and You.

6. Pharmasset. Randomized, Double-Blind, Placebo-Controlled, Multicenter Study Exploring the Safety, Tolerability, and Antiviral Effect of Substituting 600 mg Racivir for 3TC in HIV-Infected Subjects Who Have the M184V Mutation and Are Currently Failing on a HAART Regimen Containing Lamivudine. In: Bethesda (MD): National Library of Medicine (US). Registered on July 18, 2005. NLM Identifier: NCT00121979. Last accessed May 29, 2013.

7. Cahn P, Sosa N, Wiznia A, et al. Racivir Demonstrates Safety and Efficacy in Patients Harboring HIV with the M184V Mutation and <3 TAM. Abstract presented at: 14th Conference on Retroviruses and Opportunistic Infections (CROI); February 25-28, 2007; Los Angeles, CA. Abstract 488.

8. Herzmann C, Arastèh K, Murphy RL, et al. Safety, pharmacokinetics, and efficacy of (+/-)-beta-2',3'-dideoxy-5-fluoro-3'-thiacytidine with efavirenz and stavudine in antiretroviral-naïve human immunodeficiency virus-infected patients. Antimicrob Agents Chemother. 2005 Jul;49(7):2828-33.

Last Reviewed: May 29, 2013

Last Updated: May 29, 2013

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