A Phase 1 interventional study of CITY-FXI and Placebo in Factor V Leiden, Prothrombin G20210A and Venous Thromboembolism (VTE), sponsored by City Therapeutics. Recruiting at 1 site in United Kingdom. Open to participants aged 18 Years to 65 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-11-09.
Sponsored by City Therapeutics · Phase 1, Interventional, and Treatment
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 study will be conducted in three parts:
712 studies on the registry are indexed under Venous Thromboembolism; 146 are open to participants now.
This study's planned enrollment of 182 is below the median of 240 across 401 interventional studies indexed under Venous Thromboembolism.
Browse Venous Thromboembolism studies →City Therapeutics is the lead sponsor of 2 studies on the registry; 2 are open to participants now.
Counted across the registry records on this site, refreshed daily.
The criteria were revised on the registry on Nov 9, 2026. See what changed
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Childbearing potential
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Clinically significant
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Drug: CITY-FXI
Drug: Placebo
Drug: CITY-FXI
Drug: Placebo
Drug: CITY-FXI
Drug: Placebo
siRNA (subcutaneous injection)
Saline (subcutaneous injection)
Incidence, severity, and relationship of treatment-emergent adverse events (TEAEs)
To evaluate the safety and tolerability of a single dose of CITY-FXI in healthy adults and adults with Factor V Leiden (FVL) or prothrombin G20210A mutation, and of a multiple dose regimen of CITY-FXI in adults with FVL or prothrombin G20210A mutation and/or a history of provoked VTE
Time frame: Through study completion, up to Day 360 (Parts A and B) or Day 450 (Part C)
Maximum plasma concentration (Cmax)
To characterize the pharmacokinetics (PK) of a single dose of CITY-FXI in healthy adults and adults with FVL or prothrombin G20210A mutation, and of a multiple dose regimen of CITY-FXI in adults with FVL or prothrombin G20210A mutation and/or a history of provoked VTE
Time frame: Day 1 to Day 3 (Parts A and B); Days 1, 2, 91, 92 (Part C)
Area under plasma concentration time curve (AUC) of CITY-FXI
To characterize the pharmacokinetics (PK) of a single dose of CITY-FXI in healthy adults and adults with FVL or prothrombin G20210A mutation, and of a multiple dose regimen of CITY-FXI in adults with FVL or prothrombin G20210A mutation and/or a history of provoked VTE
Time frame: Day 1 to Day 3 (Parts A and B); Days 1, 2, 91, 92 (Part C)
Amount excreted in urine (Ae) of CITY-FXI
To characterize the pharmacokinetics (PK) of a single dose of CITY-FXI in healthy adults and adults with FVL or prothrombin G20210A mutation
Time frame: Day 1 to Day 3 (Parts A and B)
Change from baseline in levels of plasma Factor XI (FXI)
To characterize the pharmacodynamics (PD) of a single dose of CITY-FXI in healthy adults and adults with FVL or prothrombin G20210A mutation, and of a multiple dose regimen of CITY-FXI in adults with FVL or prothrombin G20210A mutation and/or a history of provoked VTE
Time frame: Up to Day 360 (Parts A and B) or Day 450 (Part C)
Change from baseline of Factor XI (FXI) activity
To characterize the pharmacodynamics (PD) of a single dose of CITY-FXI in healthy adults and adults with FVL or prothrombin G20210A mutation, and of a multiple dose regimen of CITY-FXI in adults with FVL or prothrombin G20210A mutation and/or a history of provoked VTE
Time frame: Up to Day 360 (Parts A and B) or Day 450 (Part C)
Change from baseline in activated partial thromboplastin time (aPTT)
To characterize the pharmacodynamics (PD) of a single dose of CITY-FXI in healthy adults and adults with FVL or prothrombin G20210A mutation, and of a multiple dose regimen of CITY-FXI in adults with FVL or prothrombin G20210A mutation and/or a history of provoked VTE
Time frame: Up to Day 360 (Parts A and B) or Day 450 (Part C)
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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