NCT07064564

iSTEP-N 101b: Pharmacokinetics and Safety Study of Low- and High-Dose Naltrexone Implants vs Monthly Vivitrol in Healthy Volunteers

A Randomized, Active-comparator Controlled, Two-Dose-level Study of iSTEP-N in Healthy Adults With Long Term Safety and PK Follow-up

• Status: Not Yet Recruiting
• Phase: Phase 1
• Study type: Interventional
• Enrollment: 33 (estimated)
• Sponsor: Akyso Therapeutics, LLC · Industry
• Sex: All
• Age: 18 Years – 65 Years
• Healthy volunteers: Accepted

Summary

This Phase 1b clinical study is evaluating iSTEP-N, an investigational extended-release implant containing naltrexone, a medication used to block the effects of opioids. The implant is placed under the skin of the thigh and is designed to release medication continuously over many months. The main purpose of the study is to measure blood levels of naltrexone over time after administration of two different doses of the iSTEP-N implant and to compare those levels with the blood levels achieved by Vivitrol®, an FDA-approved injectable extended-release naltrexone given once every month. The study will enroll healthy adult volunteers aged 18 to 65 years. Participants will be randomly assigned to one of three groups: * Low-dose iSTEP-N implant * High-dose iSTEP-N implant * Monthly Vivitrol injections Participants will be followed closely for approximately 12 months to measure medication levels and monitor safety, side effects, and overall health. The study will help determine whether the iSTEP-N implant can maintain naltrexone levels comparable to or higher than those achieved with monthly injections, especially during periods when protection from relapse is most important. Participants who receive an iSTEP-N implant and still have detectable implant material or measurable medication levels at the end of the first year may continue in a long-term follow-up period lasting up to two additional years. During this period, researchers will monitor how long the implant remains detectable and how long medication continues to be released. If the implant remains after two years, participants may choose to have it surgically removed or simply end study participation. The study is sponsored by Akyso Therapeutics, LLC, with clinical operations conducted at a dedicated clinical research center and oversight provided by an independent Institutional Review Board. All participants undergo screening examinations to confirm eligibility and are carefully monitored throughout participation. Results from this study will help determine the appropriate dose of iSTEP-N for future clinical trials and support development of long-acting treatment options for opioid use disorder that may reduce the need for frequent injections.

Detailed description

Opioid use disorder (OUD) remains a major public health challenge, driven in part by relapse and overdose risk after detoxification. Extended-release naltrexone, an opioid receptor antagonist, is approved as a once-monthly intramuscular injection (Vivitrol®) and reduces relapse risk by blocking opioid effects. However, treatment adherence may be limited by the need for repeated clinic visits and injections, and drug levels decline toward the end of each dosing interval, potentially reducing protection during periods of highest relapse vulnerability. iSTEP-N is an investigational subcutaneous implant designed to provide long-term delivery of naltrexone from a biodegradable polymer matrix. After placement beneath the skin of the thigh, the implant slowly releases medication over many months and gradually resorbs. Sustained medication delivery may improve adherence compared with monthly injections and maintain opioid receptor blockade without requiring repeated dosing visits. Protocol iSTEP-N 101b is a Phase 1b study in healthy volunteers designed to further characterize pharmacokinetics and safety of extended-release naltrexone delivered via iSTEP-N implants compared with monthly injectable naltrexone. The study evaluates two implant dose levels in parallel with active-comparator treatment to determine whether the implant can maintain plasma naltrexone concentrations comparable to or exceeding those achieved with monthly injections over a one-year period. The primary focus of the study is characterization of plasma concentrations of naltrexone over time and estimation of pharmacokinetic parameters that describe drug exposure following implant placement. Secondary analyses include evaluation of concentrations of the major metabolite, 6β-naltrexol, and assessment of safety and tolerability across treatment groups. Because the investigational product is a drug-device combination, the protocol also evaluates implant site outcomes and the duration of implant detectability and drug release. Participants receiving iSTEP-N who continue to have detectable implant material or measurable naltrexone levels after the first year may enter a long-term follow-up phase. This phase allows investigators to determine how long the implant continues to release drug and when the implant is no longer detectable by clinical examination or imaging. The study design incorporates staged enrollment and independent safety monitoring to ensure early identification of any safety concerns during implant administration and follow-up. Frequent safety assessments are performed throughout participation, including monitoring for implant site reactions and systemic adverse effects associated with naltrexone. Results from this study are intended to guide dose selection and study design for subsequent clinical development of long-acting naltrexone implants aimed at reducing barriers to sustained opioid relapse prevention therapy.

Conditions

• Opioid Use Disorder

Interventions

Type	Name	Description
DRUG	Naltrexone implant, 14.4 grams	Subcutaneous bioresorbable implant containing 14.4 grams of naltrexone, inserted into the thigh on Day 1 and designed to release drug steadily over 12 months.
DRUG	Naltrexone implant, 9.6 grams	Subcutaneous bioresorbable implant containing 9.6 grams of naltrexone, inserted into the thigh on Day 1 and designed to release drug steadily over 12 months.
DRUG	Extended-release naltrexone injection, 380 mg	Intramuscular injection of 380 mg extended-release naltrexone (Vivitrol), administered every 4 weeks for 12 months as the active comparator.

Timeline

• Start date: 2026-04-01
• Primary completion: 2027-06-01
• Completion: 2029-03-31
• First posted: 2025-07-14
• Last updated: 2026-02-05

Regulatory

• FDA-regulated drug study