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CITY-FXI safety study in healthy adults and people prone to clots

Tests CITY-FXI in healthy adults and people prone to blood clots.

Key facts

Who runs it
City Therapeutics
Where
United Kingdom1 site in 1 countryChoose a country to see its sites
Trial code
Registry title
A Study to Assess the Safety, Tolerability, Pharmacokinetics and Pharmacodynamics of CITY-FXI in Healthy Adults, Adults With FV Leiden or Prothrombin G20210A Mutation, and Adults With a History of Provoked Venous Thromboembolism
Status
Recruiting
Phase
Phase 1
People taking part
182 people, planned
Started
22 Jan 2026
Expected to end
Apr 2028
Type of study
Interventional, 6 groupsOne group gets a placebo (a dummy treatment), for comparison.
Treatments tested
  • CITY-FXI
  • Placebo
Record updated
9 November 2026

Who can take part

AI summary

From the trial's eligibility criteria. Machine-read from the registry text on this page, so it can be wrong. The registry text below and the trial team decide who can take part.

The trial is looking for healthy adults, adults with the Factor V Leiden or prothrombin G20210A gene change, and adults who had a provoked blood clot in a vein (VTE). It tests CITY-FXI against placebo.

Age
Part A: 18 to 45 years. Part B: 18 to 60 years. Part C: 18 to 65 years.
Sex
All sexes can join. In Part A, women can join only if they cannot become pregnant. In Parts B and C, women who can become pregnant must use highly effective birth control.
Disease stage
Part A: healthy adults. Part C: a provoked blood clot in a vein (VTE) within the last 10 years, and/or the gene change. Body Mass Index (BMI) 18 to 25 kg/m2 in Parts A and B, 18 to 35 kg/m2 in Part C. Weight at least 50 kg (110 lb).
Earlier treatment
People who have had any experimental drug before cannot join.
Biomarker or test result
Part B: genetic testing must confirm FVL or prothrombin G20210A mutation. Part C: a blood clot history and/or a confirmed heterozygous FVL or prothrombin G20210A mutation, meaning one changed copy of the gene.

Main reasons for not taking part

  • Any serious body-wide disease, such as heart, liver or cancer conditions
  • Any bleeding disorder, now or in the past
  • Serious bleeding that started on its own in the past
  • Any experimental drug taken before
  • Parts B and C: two changed copies of the gene (homozygous), or more than one clotting gene change, such as FVL together with prothrombin G20210A

The registry criteria, word for word

Show all 12 criteriaShow less

Who can take part

  • Males and women of non-childbearing potential (WONCBP) aged 18 to 45 years (inclusive, for Part A only)
  • Male and female participants aged 18 to 60 (inclusive, for Part B only), and aged 18 to 65 years (inclusive, for Part C only)
  • Body Mass Index (BMI) between 18 and 25 kg/m2 (inclusive, for Parts A and B only) and 18 and 35 kg/m2 (inclusive, for Part C only) and a minimum weight of 50 kg (Parts A, B, and C)
  • Ability and willingness to comply fully with all study procedures and lifestyle considerations
  • Confirmed diagnosis of FVL or prothrombin G20210A mutation via genetic testing (Part B only)
  • Women of childbearing potential (WOCBP) must agree to use acceptable highly effective contraceptive methods (Parts B and C only)
  • History of provoked venous thromboembolism (VTE) within the last 10 years and/or confirmed diagnosis of heterozygosity for FVL or prothrombin G20210A mutation via genetic testing (Part C only)

Who cannot take part

  • Prior treatment with an investigational agent
  • Any clinically significant systemic disease or disorder, including but not limited to cardiovascular, hepatic, or oncological conditions
  • History or evidence of any bleeding disorders
  • History of clinically significant spontaneous bleeding
  • Confirmed diagnosis of homozygous mutations, or combined thrombophilic defects (e.g., FVL with prothrombin G20210A mutation) (Parts B and C only)

Check if you might fit

Answer for yourself. This is not a decision: only the study team can say whether you can take part.

  • Are you between 18 and 65 years old?

This trial has no sites in United States.

It has sites in one country. Choose a country to see its sites.

About the trial

What the trial wants to find out

This is a first-in-human (FIH), single-center, randomized, double-blind, placebo-controlled, single ascending and multiple dose study evaluating the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of CITY-FXI in healthy adults, adults with Factor V Leiden (FVL) or prothrombin G20210A mutation, and adults with a history of provoked venous thromboembolism (VTE).

The 6 groups in the trial

  • CITY-FXI in Healthy Adults (Part A)Treatment being tested

    Treatment: CITY-FXI

  • In Healthy Adults (Part A)Placebo, for comparison

    Treatment: Placebo

  • CITY-FXI in Adults with Factor V Leiden or Prothrombin G20210A Mutation (Part B)Treatment being tested

    Treatment: CITY-FXI

  • In Adults with Factor V Leiden or Prothrombin G20210A Mutation (Part B)Placebo, for comparison

    Treatment: Placebo

  • CITY-FXI in Adults with FVL, Prothrombin G20210A Mutation, and/or a History of Provoked VTE (Part C)Treatment being tested

    Treatment: CITY-FXI

  • In Adults with FVL, Prothrombin G20210A Mutation, and/or a History of Provoked VTE (Part C)Placebo, for comparison

    Treatment: Placebo

Questions to ask the study team

  1. How often do I need to come in, and for how long each time?
  2. Are travel costs paid?
  3. Can I keep my own doctor?
  4. What happens if I want to stop?

Contact the study team: see the registry record → Contacts and Locations

Print a page for my doctor

Data and sources

Registry record
Listed on ClinicalTrials.gov.
Official title
A Phase 1, Randomised, Double-Blind, Placebo-Controlled Single Ascending and Multiple Dose Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of CITY-FXI, a FXI Targeting siRNA, Administered Subcutaneously in Healthy Adults, Adults With Factor V Leiden or Prothrombin G20210A Mutation, and Adults With a History of Provoked Venous Thromboembolism
Plain-language title
CITY-FXI safety study in healthy adults and people prone to clotsGenerated from the registry record. The registry title is the official one.
AI summary
From the trial's eligibility criteria. Read by machine on 15 November 2026.
Fit questions
Built from NCT07430397, who can take part
Record updated
9 November 2026