A phase 1 trial in healthy adults and adults with increased inherited risk of developing blood clots

A phase 1, randomised, double-blind, placebo-controlled single ascending dose study to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of CITY-FXI, a FXI targeting siRNA, administered subcutaneously in healthy adults and adults with factor V Leiden or prothrombin G20210A mutation

Status

Recruiting

Phases

Phase 1

Study type

Interventional

Source

ISRCTN

Registry ID

ISRCTN45090913

Enrollment

128

Registered

2026-01-19

Start date

2026-01-22

Completion date

Unknown

Last updated

2026-02-16

For informational purposes only — not medical advice. Sourced from public registries and may not reflect the latest updates. Terms

Conditions

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

Interventions

The study will be conducted in two parts: Part A: Single Ascending Dose in Healthy Adults Part B: Single Ascending Dose in Adults with Factor V Leiden (FVL) or Prothrombin G20210A Mutation Part A

Eligibility

Sex/Gender

All

Age

18 Years to 60 Years

Inclusion criteria

Inclusion criteria: 1. Males and women of non-childbearing potential (WONCBP) aged 18 to 45 years (Part A only) 2. Male and female participants aged 18 to 60 years (Part B only) 3. Body Mass Index (BMI) between 18 and 25 kg/m2 (inclusive) and a minimum weight of 50 kg 4. Ability and willingness to comply fully with all study procedures and lifestyle considerations 5. Confirmed diagnosis of FVL or prothrombin G20210A mutation via genetic testing (Part B only) 6. Women of childbearing potential (WOCBP) must agree to use acceptable highly effective contraceptive methods (Part B only)

Exclusion criteria

Exclusion criteria: 1. Any clinically significant systemic disease or disorder, including but not limited to cardiovascular, hepatic, or oncological conditions 2. History or evidence of any bleeding disorders 3. History of clinically significant spontaneous bleeding 4. Prior treatment with an investigational agent 5. Confirmed diagnosis of homozygous mutations, or combined thrombophilic defects of (Part B only)

Design outcomes

Primary

Measure	Time frame
Incidence, severity, and relationship of treatment emergent adverse events (TEAEs) measured using data collected from electronic Case Report Forms (eCRF) throughout and up to the end of the study.	—

Secondary

Measure	Time frame
1. Change from baseline in levels of plasma Factor XI (FXI) antigen, FXI activity, and activated partial thromboplastin time (aPTT) measured using validated FXI antigen, FXI activity, and aPTT assays, respectively, on Days -1, 1, 3, 8, 15, 22, 29, 36, 43, 50, 57, 85, 113, 141, 180, up to two additional follow-up visits on Day 270 and 360, and at the end of the study 2. Plasma and urine single dose PK parameters of CITY-FXI measured using validated LC/MS drug analysis methods on study Days 1, 2, and 3	—

Measure

Time frame

1. Change from baseline in levels of plasma Factor XI (FXI) antigen, FXI activity, and activated partial thromboplastin time (aPTT) measured using validated FXI antigen, FXI activity, and aPTT assays, respectively, on Days -1, 1, 3, 8, 15, 22, 29, 36, 43, 50, 57, 85, 113, 141, 180, up to two additional follow-up visits on Day 270 and 360, and at the end of the study 2. Plasma and urine single dose PK parameters of CITY-FXI measured using validated LC/MS drug analysis methods on study Days 1, 2, and 3

—

Countries

United Kingdom

Contacts

Public Contact. City Therapeutics

clinicaltrials@citytx.com+1-857-219-5440

Outcome results

None listed

Source: ISRCTN (via WHO ICTRP) · Data processed: Feb 19, 2026