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A study to evaluate the effects of CSX-1004 on breathing difficulties caused by fentanyl in healthy adults and people with opioid use disorder

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What is this trial about?

A plain-language summary of the goals, design and what participants do

This study is being conducted to evaluate the effect of CSX-1004 on respiratory depression, which is a condition where breathing becomes too slow or shallow, caused by fentanyl. The research focuses on two groups: healthy adults and individuals living with opioid use disorder, a chronic condition characterized by the problematic use of opioids. During the study, participants may receive either the test substance CSX-1004 or a placebo containing sodium chloride via IV infusion, which is a method of delivering fluids directly into a vein.

The investigation follows a specific design where participants receive different treatments in a set order to compare the results. Researchers will monitor various physical signs, such as the respiratory rate, which is the number of breaths taken per minute, and oxygen saturation, which measures the amount of oxygen in the blood. Other factors being observed include apnea, which is a temporary pause in breathing, and changes in pupil diameter. Additionally, participants will report their levels of alertness and how they feel regarding the effects of the substances used.

The research process

The trial runs in 3 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Administration of test or placebo substance

    An intravenous infusion (a liquid delivered directly into a vein) is administered. this infusion consists of either the test substance, csx-1004, or a placebo, which is a sodium chloride solution (salt water) containing no active medicine.

  2. Step 2

    Monitoring of respiratory response

    The effects of the substance on respiratory depression (a slowing down of breathing) caused by fentanyl (a strong pain medication) are measured.

    Changes in minute ventilation (the amount of air breathed in or out in one minute) are recorded to determine the primary effect of the medication.

    Various measurements are taken, including the respiratory rate (how many breaths are taken per minute), oxygen saturation (the level of oxygen in the blood), and tidal volume (the amount of air moved in or out of the lungs during a single breath).

  3. Step 3

    Observation of side effects and sensations

    The occurrence of apnea (a pause in breathing lasting 20 seconds or longer) and oxygen desaturation (when blood oxygen levels drop below 92%) is monitored.

    The diameter of the pupils (the black center of the eye) is measured.

    The level of alertness or drowsiness, drug effects, drug liking, and high sensations are assessed using a visual scale.

Who can join the trial?

9 criteria

  • You must give your written informed consent, which means signing a document that explains the study details before any tests begin.
  • You must be an adult, meaning you are between 18 and 55 years old.
  • Your body mass index (BMI), which is a measure of your weight compared to your height, must be between 18.0 and 32.0 kg/m².
  • You must weigh at least 50.0 kg.
  • You must be medically stable, meaning your health condition is steady and not changing rapidly, as confirmed by your medical history, a physical exam, an ECG (a test that records the electrical activity of your heart), and your vital signs (such as blood pressure and heart rate).
  • You must have a negative urine drug screen for fentanyl, which means a urine test shows no recent use of this specific strong medicine.
  • You must be willing and able to follow all study rules, including staying at the clinic (the medical facility) for a period and having blood sampling (having blood taken for testing).
  • For the specific part of the study for certain patients, you must have a diagnosis of mild or moderate opioid use disorder, which is a medical condition involving the use of drugs like opioids.
  • For that same part, you must report taking a daily amount of oral opioids, measured as MME (morphine milligram equivalents, a standard way to measure the strength of different opioids), between 30 to 120 mg for at least 3 months.

Who cannot join the trial?

5 criteria

  • You cannot join the study if you have a history of or currently have any major health problems involving your psychiatric (mental health), endocrine (hormones), hematologic (blood), hepatic (liver), immunologic (immune system), metabolic (how your body uses energy), urologic (urinary system), pulmonary (lungs), neurologic (brain and nerves), dermatologic (skin), or renal (kidneys) systems.
  • In the first part of the study, you are excluded if you have a history of or currently meet the medical definition for a substance use disorder, which is a condition where a person has trouble controlling the use of a substance, such as drugs or alcohol, even though it causes harm. This includes all substances except for caffeine.
  • In the second part of the study, you are excluded if you meet the medical definition for a substance use disorder involving any substance except for opioids, caffeine, or nicotine.
  • In the second part of the study, you are excluded if you have a history of or currently have severe opioid use disorder, which is a serious medical condition related to the long-term and harmful use of drugs like fentanyl or morphine.
  • You cannot participate if you are currently taking concomitant (other drugs taken at the same time) medications that are not allowed in this study and that cannot be safely stopped before you receive the first dose of the study drug.
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Investigated drugs

CSX-1004 is an experimental medication administered through an intravenous infusion. It is being studied to see if it can help prevent or reverse the slowing of breathing caused by the use of fentanyl.

What is already known about the treatment

  • CSX-1004

    This experimental drug is administered as a solution through an intravenous infusion directly into a vein. Currently being studied in clinical trials, it is being tested for its ability to help reverse breathing problems caused by opioids like fentanyl. It works at a molecular level by targeting specific receptors in the brain to prevent them from slowing down the body's natural urge to breathe. This substance is classified as an investigational medication for treating opioid-induced respiratory issues.

  • Sodium chloride

    This substance is administered as a solution through an intravenous infusion into a vein. It is a widely used, standard medical substance often used as a placebo in clinical trials to compare against new drugs. It functions as a simple salt solution that helps maintain the body's fluid and electrolyte balance without directly affecting brain receptors. This medication is pharmacologically classified as a saline solution used for fluid replacement.

Investigated diseases

Opioid use disorder - This condition is characterized by a problematic pattern of using opioid medications. It often involves a strong desire or compulsion to use these substances despite the negative effects they may cause. Over time, the brain's chemistry changes, leading to a decreased ability to control the urge to use. This process can result in a physical or psychological dependence on the drugs. The condition typically progresses as the body becomes more accustomed to the substances, requiring higher amounts to achieve the same effects.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IITrial ID2025-524133-33-00Protocol codeCSX-1004.201Estimated enrolment24 patientsSponsorCessation Therapeutics Inc.

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