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A Phase 2 Safety, Tolerability, PK, and Efficacy Study of CS-1103 Following Fentanyl Challenge With Naloxone Blockade

A Phase 2 Randomized, Double-Blind, Placebo-Controlled Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Efficacy of a Single Dose of Intravenous CS 1103 Following a Single Intravenous Dose of Fentanyl in Healthy Subjects With Naloxone Blockade

Who can join

Ages 18 to 55 · All sexes · Healthy volunteers welcome

Major Inclusion Criteria:

1. Healthy participants aged 18 to 55 years, inclusive;
2. Have prior experience with opioids, such as from a dental procedure, chronic pain management, or previous inpatient surgical procedure;
3. A body mass index between 18.0 to 30.0 kg/m2, inclusive, and a minimum body weight of 56 kg;
4. Females must not be lactating and must have a negative pregnancy test during screening and admission.

Major Exclusion Criteria:

1. Estimated glomerular filtration rate \<90 mL/min/1.73 m2;
2. History of cardiovascular disease;
3. History of any clinically important disease or disorder which, in the opinion of the Investigator, may interfere with safe study participation.

About the study

The purpose of the study is to evaluate the safety, tolerability, pharmacokinetics, and efficacy of CS-1103 (1,000 mg), given by intravenous (IV) infusion in healthy participants in the presence of a clinically relevant dose of fentanyl (200 μg, IV), with naloxone blockade (400 μg, IV).

What is being tested

• Naloxone Hydrochloride (drug)
• Fentanyl (drug)
• Sterile Saline (drug)
• CS-1103 (drug)

Sponsor: Clear Scientific, Inc. · Participants: 16 · Started: May 28, 2026

Contact the study team

• Anna Del Rosario, B.S. · Phone: 617-621-8500
• Piercen Oliver, Ph.D. · Phone: 617-621-8500

Official record on ClinicalTrials.gov — NCT07459166

Locations in the U.S.

From ClinicalTrials.gov, data retrieved Oct 2, 2026. Each study sets its own eligibility; the study team decides who can join.