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Safety, Tolerability and Pharmacokinetics of MK-4318 in Healthy Adult Participants for Acute and Chronic Pain

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What is this trial about?

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

The investigation focuses on people who experience Acute and chronic pain and evaluates a new oral capsule containing the experimental drug MK-4318. The capsules are taken by mouth in a single dose, and a matching inactive capsule (placebo) is also used for comparison.

The aim of the study is to determine how safe the medicine is, how well it is tolerated, and how the body absorbs and eliminates it after a single dose. Participants receive one dose of the study drug or placebo, then remain in the clinic for several hours while staff check vital signs, ask about any uncomfortable feelings, and collect small blood samples to track the medicine’s level in the bloodstream over time. Different groups receive increasing dose amounts, allowing researchers to observe any changes in safety or drug behavior as the dose rises.

The research process

The trial runs in 7 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial enrollment and consent

    After joining the study, you will sign an informed consent form that explains the purpose of the trial and what will be required of you.

    The consent process ensures that you understand the study procedures, risks, and your right to withdraw at any time.

  2. Step 2

    Baseline health evaluation

    A series of basic health checks will be performed, including measurement of vital signs (blood pressure, heart rate, temperature) and a brief physical examination.

    Blood and urine samples may be collected to establish your normal laboratory values before receiving any study medication.

  3. Step 3

    Random assignment to study medication

    You will be randomly assigned to receive either the active drug mk-4318 or a placebo that looks identical.

    The assignment is concealed, meaning neither you nor the study staff will know which product you receive until the study is completed.

  4. Step 4

    Administration of a single oral dose

    You will swallow one 600 mg oral capsule of the assigned product with a sip of water.

    The dose is taken only once during the entire study.

  5. Step 5

    Post‑dose monitoring and blood sampling

    After taking the capsule you will remain in the clinic for a monitoring period that lasts up to 24 hours.

    Blood samples will be drawn at several time points to measure the amount of mk-4318 in your bloodstream. typical sampling times include before the dose, and at approximately 0.5, 1, 2, 4, 8, 12, and 24 hours after the dose.

    These samples help determine how quickly the drug is absorbed, how high the concentration becomes, and how long it stays in the body.

  6. Step 6

    Assessment of safety and tolerability

    Throughout the monitoring period you will be asked about any feeling of discomfort, such as nausea, headache, or other symptoms that could be related to the study medication.

    Any such symptoms are recorded as adverse events and are evaluated by the study team.

  7. Step 7

    Final evaluation and discharge

    At the end of the 24‑hour observation you will undergo a final set of vital sign measurements and a brief health check.

    Once the study staff confirm that you are stable and no serious adverse events have occurred, you will be discharged from the clinic.

    You may be asked to complete a short follow‑up questionnaire by phone or electronic message in the days after the visit to report any delayed symptoms.

Who can join the trial?

4 criteria

  • Have a body mass index (BMI) between 18 and 30 kg/m² for Part 1, or between 18 and 32 kg/m² for Part 2 (BMI is a number that shows if your weight is healthy for your height).
  • Be assigned male sex at birth, be between 18 and 45 years old, and be taking part in Part 1.
  • Be assigned female sex at birth, be between 18 and 60 years old, and be taking part in Part 2.
  • Be a healthy volunteer who can understand the study and give informed consent (agree to join after learning what will happen).

Who cannot join the trial?

10 criteria

  • Has a history of serious problems with endocrine (hormone) systems, gastrointestinal (GI) (digestion) organs, cardiovascular (heart and blood vessels) health, hematological (blood) conditions, hepatic (liver) disease, immunological (immune system) issues, renal (kidney) function, respiratory (breathing) problems, genitourinary (urinary and reproductive) abnormalities, or major neurological (brain and nerve) disorders such as stroke or ongoing seizures.
  • Is a current smoker or has used any nicotine products (including nicotine patches or e‑cigarettes) within the past 3 months.
  • Is mentally or legally unable to give consent, has significant emotional problems now or expected during the study, or has had a serious psychiatric disorder (mental illness) in the last 5 years.
  • Has ever been diagnosed with cancer (malignancy).
  • Tests positive for hepatitis B surface antigen (HBsAg), hepatitis C antibodies, or human immunodeficiency virus (HIV), which are infections that affect the liver or immune system.
  • Had major surgery or donated/lost about 500 mL (one unit) of blood within the 4 weeks before screening.
  • Has a history of irregular heart rhythm (cardiac arrhythmia) or repeated unexplained fainting (syncopal events).
  • Has a first‑degree relative (parent, sibling, or child) with unexplained fainting, sudden cardiac arrest, or a known inherited heart rhythm problem such as Brugada syndrome.
  • Has taken part in another experimental drug study within the last 4 weeks (or longer, depending on how long the previous drug stayed in the body).
  • Shows any of the following heart‑related findings: a corrected QT interval (QTcF) longer than 450 milliseconds for men or 470 milliseconds for women; personal or family risk factors for a dangerous rhythm called Torsades de Pointes (such as heart failure or a family history of long QT syndrome); untreated low potassium (hypokalemia) or low magnesium (hypomagnesemia); or is taking medicines that lengthen the QT/QTcF interval.
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Investigated drugs

MK-4318 is an experimental oral capsule being studied for the first time in humans. In this trial, healthy adult volunteers take a single dose of the capsule, and the dose is increased in later groups. The main goals are to see whether the drug is safe, to understand how well participants can tolerate it, and to measure how the drug is absorbed, distributed, and cleared from the body (its pharmacokinetics). This information helps researchers decide if the medication can move on to further testing.

What is already known about the treatment

MK-4318 - MK-4318 is taken as an oral capsule, with a single dose of 600 mg swallowed with water. It is currently an experimental drug being studied in early‑phase clinical trials and has not yet been approved for any use. The compound is being investigated for the relief of acute and chronic pain. It works by blocking specific pain‑signal pathways at the nerve‑cell level, and is classified as an investigational small‑molecule analgesic.

Investigated diseases

  • Acute pain

    Acute pain is a short‑lasting sensation that arises suddenly after tissue injury or inflammation. It typically peaks quickly and resolves as the underlying cause heals, usually within days to weeks. The pain signals are transmitted by peripheral nerves and processed by the brain, alerting the body to potential harm. As healing progresses, the intensity diminishes and the sensation disappears.

  • Chronic pain

    Chronic pain persists beyond the normal healing time, often defined as lasting longer than three months. It may start after an acute injury but continues even after the original cause has resolved, or it can develop without a clear initiating event. Ongoing nerve signaling and changes in the nervous system can amplify the perception of pain over time. The condition can fluctuate, with periods of higher intensity interspersed with milder episodes.

Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase ITrial ID2023-503360-16-00Protocol codeMK-4318-001Estimated enrolment32 patientsSponsorMerck Sharp & Dohme LLC

sourced from the EU Clinical Trials Register and site verification

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