The study of vicriviroc as an entry inhibitor HIV medicine was discontinued in 2010. The company developing the drug announced that this decision was based on data from one Phase II trial in treatment-naive adults and two Phase III trials in treatment-experienced adults. In these trials, vicriviroc failed to show improved efficacy over currently approved HIV medicines already in use.3-5
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.
Vicriviroc is an investigational drug that was studied for the treatment of HIV infection.
Vicriviroc belongs to a class (group) of HIV drugs called entry and fusion inhibitors.2 Entry and fusion inhibitors block HIV from getting into and infecting certain cells of the immune system. This prevents HIV from multiplying and can reduce the amount of HIV in the body.
Vicriviroc works by attaching to one of two proteins on the surface of the immune cells. These proteins are called the CCR5 and CXCR4 co-receptors. Vicriviroc attaches to the CCR5 co-receptor. When vicriviroc attaches to the CCR5 co-receptor, certain strains of HIV—called R5-tropic virus—cannot attach to, enter, or infect the cell.6
Vicriviroc requires boosting with the FDA-approved HIV medicine ritonavir (brand name: Norvir). (Boosting involves the use of a second drug to increase the effectiveness of the main [first] drug.)7
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 FDA for sale in the United States. Some drugs go through FDA’s accelerated approval process and are approved before a Phase III clinical trial is complete. After a drug is approved by 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
Vicriviroc has been studied in Phase III clinical trials.2
The development of vicriviroc for the treatment of HIV infection was discontinued in July 2010.3
In two Phase III studies (known as the VICTOR-E3 and VICTOR-E4 studies), vicriviroc taken once daily was compared with placebo (a placebo is an inactive drug that is identical in appearance to the active drug being studied) in HIV-infected adults with R5-tropic HIV (virus that uses CCR5 as a co-receptor). The participants had taken HIV medicines previously (treatment-experienced). All study participants also received an optimized background regimen containing at least two fully active drugs. (An optimized background regimen is a combination of drugs, chosen on the basis of a person’s resistance test results and treatment history, that are not being studied as the investigational drug[s] in the clinical trial, but are given to help control a participant’s HIV infection.)4,9
In a combined analysis of VICTOR-E3 and VICTOR-E4, vicriviroc plus optimized background therapy did not work any better than placebo plus optimized background therapy. The majority of study participants were receiving at least three active drugs as part of their optimized background regimens. In an analysis of study participants receiving two or fewer active drugs in their background regimens, vicriviroc proved to be more effective than placebo. In terms of safety, vicriviroc was comparable to placebo.4,9
In a Phase II study, vicriviroc taken once daily was compared with the FDA-approved combination drug emtricitabine/tenofovir disoproxil fumarate (brand name: Truvada) in adults infected with R5-tropic HIV. The participants had never taken HIV medicines before entering the study (treatment-naive). All study participants also received a background regimen containing the FDA-approved protease inhibitors atazanavir (brand name: Reyataz) and ritonavir (brand name: Norvir).5 (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.)
In this study, the vicriviroc regimen had similar anti-HIV activity as the Truvada regimen. Anti-HIV activity was measured as a drop in viral load (the amount of HIV in a blood sample) from the time of study entry to Week 48. However, in terms of efficacy, vicriviroc did not appear to work as well as Truvada. Efficacy was measured as the proportion of participants in each treatment group that had a viral load fewer than 50 copies/mL at Week 48. In terms of safety, more participants in the vicriviroc group discontinued the study because of side effects than in the Truvada group.5
In the Phase III studies discussed under the previous question, side effects were similar in both the vicriviroc and placebo groups. The vicriviroc group had a greater percentage of participants stopping the study because of side effects than the placebo group did.4,9
In the Phase II study discussed under the previous question, no common adverse events were seen in the vicriviroc group. More vicriviroc than Truvada participants discontinued the study because of side effects.5
If testing of vicriviroc begins again, additional information on possible side effects will be gathered.
More information about vicriviroc-related research studies is available from the AIDSinfo database ofClinicalTrials.gov study summaries. Click on the title of any trial in the list to see theClinicalTrials.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.
Last Reviewed: September 13, 2014