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Contact the study team using the details below to take part. If there are no contact details below please ask your doctor in the first instance.

Contact Information:

Ms Sarah Maitland-Jones
Sarah.Maitland-Jones@tmcpharma.com


Ms Ulrike Lorch
u.lorch@richmondpharmacology.com


None . City Therapeutics
clinicaltrials@citytx.com


Ms Alison Shaw
alison.shaw@tmcpharma.com


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Be Part of Research - Trial Details - A phase 1 trial in healthy adults and adults with increased inherited risk of developing blood clots
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A phase 1 trial in healthy adults and adults with increased inherited risk of developing blood clots

Recruiting

Open to: All Genders

Age: Adult

London

Medical Conditions

Factor V Leiden or prothrombin G20210A mutation in healthy adults and adults

This information is provided directly by researchers, and we recognise that it isn't always easy to understand. We are working with researchers to improve the accessibility of this information. In some summaries, you may come across links to external websites. These websites will have more information to help you better understand the study.


We are conducting this study to learn more about an investigational drug called CITY-FXI. This is not yet approved for use by drug regulatory agencies and can only be given in clinical studies. This clinical study will be the first time CITY-FXI will be given to humans. CITY-FXI is being investigated in this study to see if it is safe, tolerable, and how it affects the body.
CITY-FXI is being developed to help prevent the occurrence of thromboembolic diseases (formation of harmful blood clots). A blood clot is when blood becomes thick and sticky and forms a lump that can block blood flow. These blood clots can sometimes be life-threatening, for example, when formed in the legs (known as deep vein thrombosis) or lungs (known as pulmonary embolism).
Current medicines for thromboembolic diseases are effective but may increase the risk of serious bleeding, so there is a need for safer medicines that prevent clots without causing excess bleeding.
CITY-FXI is an investigational drug that uses a type of molecule called small interfering ribonucleic acid (siRNA). It is designed to reduce the amount of a specific protein called Factor XI (FXI). By lowering FXI, CITY-FXI could help prevent harmful blood clots with a lower bleeding risk than with currently available drugs. It is not yet known whether CITY-FXI will have this effect.

Start dates may differ between countries and research sites. The research team are responsible for keeping the information up-to-date.  

The recruitment start and end dates are as follows:

22 Jan 2026 01 Aug 2026

This study will be comprised of two parts (Part A and Part B).
Part A will include healthy participants who will be randomly assigned to receive the investigational drug (CITY-FXI) or placebo (placebo is a product that looks like and is administered in the same way as the investigational drug but does not contain the active ingredient).
Part B will include participants who have been diagnosed with Factor V Leiden (FVL) or Prothrombin G20210A mutations (variations in your genes that increase the risk of blood clot formation). Participants will be randomly assigned to receive the investigational drug (CITY-FXI) or placebo.
The planned duration of study participation could be approximately 13 months, depending on how each participant’s body responds to CITY-FXI from screening to the last visit.


Healthy volunteers aged 18 – 45 years old, and adults aged 18 – 60 years old with Factor V Leiden or Prothrombin G20210A mutation

You can take part if:



You may not be able to take part if:


1. Any clinically significant systemic disease or disorder, including but not limited to cardiovascular, hepatic, or oncological conditions2. History or evidence of any bleeding disorders3. History of clinically significant spontaneous bleeding4. Prior treatment with an investigational agent5. Confirmed diagnosis of homozygous mutations, or combined thrombophilic defects of (Part B only)


Below are the locations for where you can take part in the trial. Please note that not all sites may be open.

  • Richmond Pharmacology Limited
    1a Newcomen Street, London Bridge
    London
    SE1 1YR

There is no medical benefit to the participants of Part A of the study, as they are healthy volunteers. However, they will receive free regular health checks by participating in this study. It is hoped that the information collected in this study will help patients at risk of or with thromboembolic diseases (formation of harmful blood clots) in the future.
Participants in Part B (adults with factor V Leiden or prothrombin G20210A mutation) may or may not have a temporary reduction in thrombotic (formation of blood clots) risk. The data we get from this study will help us understand how safe the study drug is in preventing the formation of harmful blood clots. Participants will also receive free regular health checks in this study.
There are potential risks related to the investigational drug and procedures, such as bleeding, allergic reactions, and soreness or pain from the blood samples or the study drug or placebo injection. It is currently unknown if CITY-FXI will have any effects on pregnancy, breastfeeding, or unborn foetus. As this drug has not been given to humans before, the understanding of risks is based on earlier studies that were mainly conducted in animals. The Study Doctor understands these risks and can provide guidance on how these risks relate to participants when choosing to participate in the study.
If a participant gets new symptoms of an illness or become unwell during the study, they will be examined by a Study Doctor. This may involve additional safety tests (including urine and blood tests, vital signs, and electrocardiograms). The Study Doctor will perform a clinical assessment and ensure the condition is managed appropriately. The risks and benefits of any additional treatment will be explained to participants.

None . City Therapeutics
clinicaltrials@citytx.com


Ms Sarah Maitland-Jones
Sarah.Maitland-Jones@tmcpharma.com


Ms Ulrike Lorch
u.lorch@richmondpharmacology.com


Ms Alison Shaw
alison.shaw@tmcpharma.com



The study is sponsored by City Therapeutics Inc. and funded by City Therapeutics, Inc.



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Read full details for Trial ID: ISRCTN45090913
Last updated 02 February 2026

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