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Phase 2 Study of ALN-6400 Safety and Tolerability in Female Patients with Von Willebrand Disease and Heavy Menstrual Bleeding

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What is this trial about?

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

The study involves women who have Von Willebrand Disease, a bleeding disorder that makes it hard for blood to clot, and who also experience Heavy Menstrual Bleeding, which means losing a larger amount of blood during periods. The investigational medicine being tested is called ALN-6400, which is given as a subcutaneous injection, meaning the medicine is placed just under the skin.

The main aim of the study is to evaluate how safe and well‑tolerated multiple doses of the medicine are in this patient group. Participants will receive a series of injections over several weeks, with regular clinic visits where vital signs, heart rhythm checks, and blood tests are performed to watch for any unwanted effects. Some participants may receive a harmless inactive substance for comparison, but the study staff will not know which person receives which treatment.

During the study period, blood samples are taken to measure the activity of the clotting protein that is low in this condition, and menstrual blood loss is recorded using a simple diary that helps estimate the amount of blood lost each cycle. After the dosing phase, participants continue to be followed for a short time to ensure any delayed effects are captured. All procedures are designed to be as short and comfortable as possible.

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

    Enrollment and consent

    After the patient joins the study, written information about the trial is provided and informed consent is obtained.

  2. Step 2

    Baseline assessments

    Initial measurements are taken, including vital signs, electrocardiogram (ecg), laboratory tests, and assessment of menstrual blood loss using the pictorial blood assessment chart (pbac).

    Blood samples are collected to determine baseline plasma activity of the von willebrand factor (plg) and other protein levels.

  3. Step 3

    Randomization and blinding

    The patient is assigned by a computer system to receive either aln-6400 or a matching placebo, and the assignment is concealed from the patient and study staff (double-blind, randomized).

  4. Step 4

    First dose administration

    The first dose of aln-6400 is given as a subcutaneous injection of 50 mg in a sterile solution for injection.

    The injection is performed by trained personnel at the study site.

  5. Step 5

    Subsequent dosing visits

    Additional doses of aln-6400 are administered according to the study schedule, each dose being a subcutaneous injection of 50 mg.

    The exact interval between doses is defined in the protocol and followed by the patient.

  6. Step 6

    Ongoing safety monitoring

    At each visit, vital signs, ecg, and laboratory tests are repeated to monitor for adverse events.

    The patient reports any symptoms or side effects experienced since the previous visit.

  7. Step 7

    Efficacy evaluations

    Menstrual blood loss is recorded using the pbac tool at designated times to assess change from baseline.

    Blood samples are taken to measure changes in plg activity and plasma protein levels.

    Patient‑reported outcome questionnaires, including the patient‑global impression of change (pgic) and severity (pgis), are completed.

  8. Step 8

    Study completion

    The final visit occurs near the estimated end date of the trial (2027‑06‑30).

    All final safety and efficacy measurements are performed, and the study drug is discontinued.

Who can join the trial?

7 criteria

  • Age and sex: You must be a female who is at least 18 years old and no older than 45 years. If you are using combined oral contraceptive pills (birth‑control pills) that contain a low amount of estrogen (35 µg or less per day), the upper age limit is 34 years.
  • Diagnosis of von Willebrand Disease (VWD): You need a confirmed diagnosis of VWD. This includes any of the following types: type 1, type 2 (any subtype), type 3, or platelet‑type VWD. For type 1, a blood test called VWF activity (VWF:Act) must show a level below 30 IU/dL, or between 30 and 40 IU/dL together with a bleeding score higher than 5 on the ISTH‑BAT questionnaire (a tool that measures how much you bleed). The VWF activity test measures how well a protein in your blood helps clotting.
  • Heavy menstrual bleeding (HMB): During the screening period you must have had two menstrual cycles with a pictorial blood assessment chart (PBAC) score greater than 100. The PBAC is a diary where you record the amount of blood on pads or tampons, and a score above 100 indicates heavy bleeding.
  • Stable menstrual‑bleeding treatment: Your usual treatment for heavy periods must be stable and not change during the double‑blind part of the study, except for rescue medicines if needed. You must stop taking tranexamic acid (TXA) and other medicines that stop bleeding (called antifibrinolytics) before the first day of the study, and you must stop any scheduled clotting factor product (any medicine that contains von Willebrand factor or Factor VIII) before day 15.
  • Regular menstrual cycle: You must have periods that occur every 21 to 35 days, as you have reported for the six months before screening.
  • Body‑mass index (BMI) limit: If you are using combined oral contraceptive pills, your BMI must be less than 30 kg/m². BMI is a calculation that compares your weight to your height.
  • Ability to follow study procedures: You must be able to understand the study, agree to take part, keep a daily menstrual‑bleed diary with PBAC scores for at least two full cycles during screening, and sign a written informed consent form.

Who cannot join the trial?

34 criteria

  • Having liver test results that are too high: specifically, liver enzymes called ALT or AST more than twice the normal range, total bilirubin (a waste product processed by the liver) more than 1.5 times normal (unless you have Gilbert’s syndrome and it is less than twice normal), or a blood clotting test called INR greater than 1.1.
  • Having poor kidney function measured by an estimated glomerular filtration rate (eGFR) below 30 mL/min/1.73 m².
  • Having a low level of red blood cells, shown by a hemoglobin value under 8 g/dL.
  • Having a low platelet count (the cells that help blood clot) below 100,000 per microliter, except for certain types of VWD where the cutoff is 50,000.
  • Using certain hormone medicines (such as gonadotropin‑releasing hormone agonists or systemic estrogen hormone‑replacement therapy) within the past 12 weeks, unless you are on a low‑dose combined oral contraceptive that meets specific timing rules.
  • Having taken any experimental (investigational) drug within the last 30 days or five drug half‑lives before screening.
  • Having taken, within the past 24 weeks, or planning to take any RNA‑interference (RNAi) or antisense oligonucleotide therapy that is not the study drug.
  • Planning to change any allowed medication for heavy menstrual bleeding that could affect your periods during the study.
  • Having a new hormonal or non‑hormonal intrauterine device (IUD) or hormonal implant placed within the past 24 weeks.
  • Using an etonogestrel implant (a type of long‑acting birth control) within the past 24 weeks or planning to use one during the study.
  • Taking blood‑thinning medicines (anticoagulants) such as warfarin, apixaban, rivaroxaban, or dabigatran now or planning to start them.
  • Taking medicines that stop platelets from working, including aspirin, now or planning to start them (other pain relievers called NSAIDs are allowed).
  • Receiving regular factor replacement therapy (at least one infusion each week for the past 12 weeks) within the past 4 weeks or planning to continue it, except for short‑term use for menstrual bleeding that must stop before day 15 of the study.
  • Being unable or unwilling to avoid antifibrinolytic drugs such as tranexamic acid (TXA) or aminocaproic acid during the blinded and extension phases.
  • Having any current gynecological condition that causes abnormal uterine bleeding, such as infection, fibroids, endometriosis, polycystic ovary syndrome (PCOS), or cervical dysplasia.
  • Having any other bleeding disorder besides von Willebrand disease.
  • Having acquired (non‑inherited) von Willebrand disease.
  • Having untreated hypothyroidism, shown by a high thyroid‑stimulating hormone (TSH) level within three months if you have a history of thyroid problems.
  • Having uncontrolled high blood pressure (hypertension) as judged by the study doctor.
  • Having an unresolved acute bleeding episode that could interfere with the study or put your safety at risk.
  • Having a known inherited clotting problem such as hereditary thrombophilia, thrombotic thrombocytopenic purpura, antiphospholipid antibody syndrome, or any other clotting disorder.
  • Having a history of a blood clot (thrombosis or thromboembolism) confirmed by ultrasound or other imaging.
  • Having a ligneous lesion (a thick, wood‑like growth) on physical exam, or a lesion that might be mistaken for one.
  • Planning major surgery during the study period or any planned procedure to treat heavy menstrual bleeding (for example, endometrial ablation).
  • Having had a liver transplant or being on an active waiting list for a liver transplant during the treatment period.
  • Having other medical problems that the investigator believes would make it difficult to follow the study or could be unsafe.
  • Having many drug allergies or an allergic reaction to any part of the study medication.
  • Being unable to tolerate a subcutaneous (SC) injection (an injection given under the skin).
  • Not willing to follow the study’s birth‑control requirements.
  • Being pregnant, trying to become pregnant, or breastfeeding.
  • Being unable or unwilling to limit alcohol intake; drinking more than two standard drinks per day (one drink = one glass of wine, one shot of spirits, or half a pint of beer) excludes you.
  • Having an alcohol use disorder in the past 12 months, as judged by the investigator.
  • Having a substance‑use disorder that the investigator thinks would affect your ability to follow study procedures.
  • If you are using combined oral contraceptives, having smoked tobacco within the past 12 months.
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Investigated drugs

ALN-6400 is an experimental medicine that contains a specially designed piece of RNA. This RNA is meant to help the body produce more of a protein called von Willebrand factor, which is low in people with von Willebrand disease. In the study, the medicine is given by a small injection under the skin. Researchers are testing whether giving several doses of ALN‑6400 is safe, well‑tolerated, and able to reduce heavy menstrual bleeding in women who have this condition.

What is already known about the treatment

ALN-6400 - ALN-6400 is given as a sterile solution for subcutaneous injection, typically 50 mg per dose. It is still investigational and is being studied in a Phase 2 trial, so it is not yet approved for general medical use. The drug is designed to treat women with von Willebrand disease who have heavy menstrual bleeding. It works by using a short piece of RNA to silence a specific gene, lowering the amount of a protein that contributes to abnormal bleeding, and it belongs to the class of RNA‑based (siRNA) therapeutics.

Investigated diseases

  • Von Willebrand disease

    Von Willebrand disease is an inherited bleeding disorder caused by a shortage or malfunction of von Willebrand factor, a protein that helps blood clot. People may notice easy bruising, frequent nosebleeds, or prolonged bleeding after cuts. In women, it often leads to heavier menstrual bleeding. The condition is present from birth and its severity can change over time, sometimes worsening during hormonal changes or pregnancy. Symptoms may become more noticeable as the individual grows older.

  • Heavy menstrual bleeding

    Heavy menstrual bleeding, also called menorrhagia, is a condition where menstrual flow is unusually large or lasts longer than typical. It can cause the need to change pads or tampons frequently and may interfere with daily activities. The amount of bleeding can increase over successive cycles, especially during puberty or perimenopause. Hormonal fluctuations, uterine abnormalities, or underlying clotting problems can make the bleeding become more severe. Over time, it may lead to anemia due to loss of blood.

Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IITrial ID2025-524967-19-00Protocol codeALN-6400-002Estimated enrolment21 patientsSponsorAlnylam Pharmaceuticals Inc.

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