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.
Fostemsavir (also known as BMS-663068) is an investigational drug that is being studied for the treatment of HIV infection.
Fostemsavir 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.
By attaching to the gp120 protein on the outer surface of HIV, fostemsavir blocks HIV from getting into and infecting the immune cells.3
Fostemsavir 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, fostemsavir is converted to temsavir (also known as BMS-626529).3,4
Clinical trials are conducted in phases. Each phase has a different purpose and helps researchers answer different questions.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 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.5
In a Phase IIa study (known as AI438006), two different strengths of fostemsavir were studied in HIV-infected participants who had HIV-1 subtype B. Some of the participants had never taken HIV medicines before entering the study (also called treatment-naive), and others had taken HIV medicines previously (also called treatment-experienced). The treatment-experienced participants were required to be off HIV medicines for at least 8 weeks before starting fostemsavir. Participants were assigned to one of the following five treatment groups for 8 days:
In this study, fostemsavir was shown to have substantial antiviral activity, decreasing viral load (the amount of HIV in a blood sample) from baseline. Investigators concluded that fostemsavir may be given either once or twice daily and with or without a ritonavir booster. (A booster drug is a second drug used to increase the effectiveness of the main [first] drug.) In terms of safety, there were no clinically relevant effects on electrocardiogram (ECG), laboratory values, vital signs, or physical exams. The most common side effects were mild headache and rash.3,7In a Phase IIb study (known as AI438011), investigators looked at the safety and effectiveness of several fostemsavir dosages and compared them to the safety and effectiveness of the FDA-approved protease inhibitor atazanavir (brand name: Reyataz) boosted with ritonavir (brand name: Norvir). Participants were HIV-infected, treatment-experienced adults. All participants also received a background regimen of the FDA-approved integrase inhibitor raltegravir (brand name: Isentress) and the FDA-approved nucleoside reverse transcriptase inhibitor tenofovir disoproxil fumarate (brand name: Viread). (A background regimen is a combination of drugs 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.) Participants were assigned to one of the following five dosing groups:
A sub-study of fostemsavir was also performed prior to the main study described above. During the sub-study, a portion of participants from each fostemsavir dosing group took fostemsavir alone without any other HIV medicines (also called monotherapy) for 7 days.9,10
In the main study, Week 24 results showed that fostemsavir had a similar effectiveness at reducing viral load across all fostemsavir groups and when compared to ritonavir-boosted atazanavir. In the sub-study, fostemsavir monotherapy reduced viral load after 7 days of treatment. In terms of safety, fostemsavir did not cause any serious side effects or side effects leading to study drop-outs.9,10
In the Phase IIa study discussed under the previous question, which looked at treatment with different doses of fostemsavir over 8 days, the most common side effects were mild headache and rash.7
In the Phase IIb study also discussed under the previous question, no safety concerns associated with fostemsavir treatment were identified.10
Because fostemsavir is still being studied, information on possible side effects of the drug is not complete. As testing of fostemsavir continues, additional information on possible side effects will be gathered.
More information about fostemsavir-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.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.
Last Reviewed: September 23, 2014