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Safety, Tolerability and Pharmacokinetics of Multiple Oral Doses of MK-3508 in Healthy Participants for RSV Infection

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What is this trial about?

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

The study focuses on Respiratory syncytial virus infection, a common virus that affects the breathing system, and tests an oral medication called MK-3508. The purpose of the study is to evaluate the safety and tolerability of taking multiple doses of this drug in healthy volunteers.

Participants will receive either the study drug in a hard capsule or a matching placebo for several days, with each dose taken by mouth. Blood samples will be collected at various times after dosing to assess the drug’s pharmacokinetics, which means how the medicine is absorbed, distributed, and eliminated by the body. Throughout the study, participants will be monitored for any side effects, and the study team will record any events that may require stopping the medication.

The research process

The trial runs in 8 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Baseline Assessments

    During your first visit after joining the study, you will undergo a series of health checks, including physical measurements, blood tests, and a review of your medical history.

    These assessments establish your health status before you start taking any study medication.

  2. Step 2

    Receiving Study Medication

    You will be given a supply of hard capsules to take at home. Each capsule contains 80 mg of mk-3508 or a matching placebo that looks identical.

    The study staff will explain how to store the capsules and will confirm that you understand the dosing instructions.

  3. Step 3

    Daily Oral Dosing

    You will swallow one capsule by mouth each day, preferably at the same time each day, with a glass of water.

    The capsule is taken orally, meaning it is swallowed and absorbed through the digestive system.

    You will continue this daily dosing for the entire dosing period defined by the study protocol.

  4. Step 4

    Clinic Visits for Safety Monitoring

    At scheduled intervals you will return to the clinic for safety evaluations. During each visit, staff will measure vital signs, perform physical examinations, and collect blood samples.

    These blood samples are used to assess the pharmacokinetics of the drug, which describes how the medication is absorbed, distributed, metabolized, and eliminated by your body.

  5. Step 5

    Recording Symptoms and Side Effects

    You will keep a simple diary to note any physical changes, discomfort, or other health problems you experience while taking the study medication.

    Any unwanted medical occurrence, known as an adverse event, should be recorded in the diary and reported to the study staff at your next visit.

  6. Step 6

    Completion of Dosing Period

    After the final scheduled dose of the capsule, you will stop taking the medication.

    You will be reminded to return any unused capsules to the study team during your last dosing‑period visit.

  7. Step 7

    Final Study Assessments

    A final clinic visit will be performed to repeat safety checks, collect final blood samples, and review your diary for any reported adverse events.

    The study staff will discuss the overall results of the safety and pharmacokinetic measurements with you.

  8. Step 8

    Study End and Follow‑Up

    After the final assessments, the study will be formally concluded for you. No further study medication will be required.

    If the protocol includes any post‑study follow‑up, you will be informed of the timing and purpose of that follow‑up.

Who can join the trial?

3 criteria

  • You are in good health (meaning you have no serious medical problems) and you are between 18 and 55 years old.
  • If you are able to produce sperm, you must agree not to donate sperm and you must use a condom or another reliable form of contraception (birth control) while in the study.
  • If you were assigned female at birth, you must be a person who cannot become pregnant, also called non‑childbearing potential.

Who cannot join the trial?

10 criteria

  • Has a history of serious problems with endocrine (hormone) function, gastrointestinal (digestive) system, cardiovascular (heart and blood vessels) health, hematological (blood) disorders, hepatic (liver) disease, immunological (immune) issues, renal (kidney) problems, respiratory (lung) disease, genitourinary (urinary or reproductive) abnormalities, or major neurological (brain and nerve) conditions such as stroke or ongoing seizures.
  • Regularly uses cannabis (marijuana) or other illegal drugs.
  • Is unable to make legal decisions because of mental incapacity, has major emotional problems, or has had a serious psychiatric disorder (mental illness) in the past five years.
  • Has ever had cancer (malignancy).
  • Has many or severe allergies (for example to foods, medicines, or latex), or has ever experienced an anaphylactic reaction (a life‑threatening allergic response) or strong intolerance to prescription or over‑the‑counter drugs or foods.
  • Tests positive for hepatitis B surface antigen, hepatitis C antibodies, or HIV (human immunodeficiency virus).
  • Cannot stop taking any medication, vitamins, herbal remedies, or over‑the‑counter drugs for about two weeks (or five drug half‑lives) before the first dose and throughout the study.
  • Is a smoker.
  • Consumes more than three alcoholic beverages per day.
  • Consumes more than six servings of caffeinated drinks (such as coffee, tea, or soda) per day.
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Investigated drugs

MK-3508 is an experimental oral medication being tested in this study. It is provided as a hard capsule that participants swallow. The trial is designed to see how safe the drug is, how well people can tolerate it, and how it is absorbed, distributed, and cleared from the body when taken multiple times. Healthy volunteers receive the medication at several increasing dose levels so researchers can gather detailed information about its safety and how it behaves in the body.

What is already known about the treatment

MK-3508 - This investigational drug is taken as a hard capsule taken by mouth, usually 80 mg per dose. It is currently in early clinical testing and has not yet been approved for general medical use. The study is looking at its potential to treat respiratory syncytial virus infection, a common viral illness. MK-3508 works by blocking a viral enzyme needed for the virus to copy its genetic material, and it is classified as an antiviral polymerase inhibitor.

Investigated diseases

Respiratory syncytial virus infection - It is a viral infection that primarily targets the airways of infants, young children, and older adults. The virus spreads through respiratory droplets and close contact with infected individuals. After exposure, symptoms such as runny nose, cough, and fever appear within a few days. The infection causes inflammation of the small airways, leading to wheezing and difficulty breathing. In some cases it can progress to bronchiolitis or pneumonia, with increased mucus production and breathing problems. Most episodes improve over one to two weeks, although coughing may persist for a longer period.
Trial detailsLast updated 25 Oct 2026
Age18+ yearsPhasePhase ITrial ID2023-505821-15-00Protocol codeMK-3508-002Estimated enrolment24 patientsSponsorMerck Sharp & Dohme LLC

sourced from the EU Clinical Trials Register and site verification

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