CLOTRx Healthy Volunteer Study

Study Name

Impact of Steady State Cobicistat and Darunavir/Cobicistat on the Pharmacokinetics and Pharmacodynamic of Oral Anticoagulants (Rivaroxaban, Apixaban) in Healthy Volunteers (ClotRx)

Study Number


Goal of Study

People infected with HIV take drugs called antiretrovirals to keep the amount of HIV in their bodies low. HIV, which stands for human immunodeficiency virus, is the virus that causes AIDS. For a variety of reasons, many people with HIV may also need to take medications to treat or prevent blood clots. These medications that prevent blood clots are called anticoagulants. Some people may also refer to them as blood thinners. It is important to understand how antiretrovirals and oral anticoagulants interact with each other.

Some drugs used to treat HIV may increase the amount of rivaroxaban in the body. This could lead to bleeding or other health problems. One such anti-HIV drug includes darunavir (DRV). The form of darunavir that will be given in this study has been combined with another drug, called cobicistat (COBI), in one single tablet. COBI is not an anti-HIV drug; however, it is used to increase the amount of some anti-HIV drugs in the body so that they work better. In this study, we want to learn by how much COBI or darunavir/cobicistat (DRV/COBI) will increase rivaroxaban blood levels. Results from this study group may help doctors choose the best anticoagulant medicine for HIV infected patients also taking COBI-based anti-HIV drugs. This part of the study requires testing 12 healthy people to answer the study question. We will also conduct similar testing in a group of 12 healthy people to answer this same study question with a different oral anticoagulant, apixaban (Eliquis®).

All the drugs used in this study are approved by the Food and Drug Administration (FDA). DRV is FDA approved for the treatment of HIV. COBI is used to increase blood concentrations of other anti-HIV drugs. Rivaroxaban is FDA approved for the treatment and prevention of blood clots. You do not have HIV or blood clots so you do not need these drugs for your medical care. We are asking healthy people to join this study to evaluate the blood levels of rivaroxaban when taken with COBI and DRV/COBI. These drug combinations have not been studied and the risks associated with combined use are not known.

Study Design

Before you can join this study, we have to make sure you are eligible. This is called screening. The single screening visit will last about 3-4 hours and will occur up to 90 days before the rest of the study starts. You will need to fast (not eat anything and drink only water) beginning at midnight the night before the screening visit. 

The rest of the study will take 23 – 29 days, depending on scheduling. There will be 8 visits to the NIH Clinical Center (CC). Of the 8 visits, 3 visits are long days (lasting about 10 hours) as blood samples will be collected every 1 – 2 hours following administration of rivaroxaban and COBI or DRV/COBI. The remaining 5 visits will be short days (lasting about 1 hour) as a single blood sample will be collected. You will take the COBI or DRV/COBI for 14 days, and receive the anticoagulants three times over the study period.  There are specific times when we need to collect blood samples for our study. Therefore, there is a strict calendar for when study visits will take place. We will give you a detailed study schedule to keep, and we will call to remind you of upcoming visits. 

We will recruit up to 12 participants.  Volunteers will be compensated.

Eligibility Criteria

  • You are 18-65 years old, in good general health with no active medical conditions
  • You do not take any medications, including hormonal birth control
  • You have a Body Mass Index (BMI) between 18 and 30
  • You do not use any products containing nicotine, including vaping
  • You agree not to consume any alcohol for entire study duration (about 20 days total)
  • You agree to an HIV test at screening
  • You agree to a urine drug and alcohol test at screening
  • If female, you are not pregnant, breast feeding, or planning to become pregnant in the near future

Contact Information

Volunteer or get more information
Toll free: 1-800-411-1222
TTY: 1-866-411-1010
Se habla español

Participating in Research

Watch a series of short informational videos about participating in clinical trials. These videos are intended to help potential participants understand how research works, what questions they should consider asking, and things to think about when deciding whether or not to participate in a study.

Content last reviewed on