Safety and Tolerability of Intrathecal ION337 in Patients with Dravet Syndrome

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What is this study about?

The study involves patients with Dravet Syndrome, a rare genetic condition that causes frequent and severe seizures. The investigational drug being tested is called ION337, which is given by an intrathecal injection, meaning the medicine is placed directly into the fluid surrounding the spinal cord. The purpose of the study is to evaluate the safety and tolerability of ION337 in this population. Safety checks include monitoring for any side effects, changes in blood tests, heart rhythm, and overall health assessments.

Participants will first receive a single low dose of the medication, followed by a period of observation. After this initial phase, they may receive multiple increasing doses over several weeks, with regular clinic visits to check how the drug is processed in the body and to record any changes in seizure frequency. Samples of the fluid around the brain and spinal cord (CSF) and blood are taken to understand how the drug moves through the body, and seizure counts are recorded to see if there is any improvement. Throughout the study, doctors closely watch for any adverse events and adjust the plan as needed.

1 enrollment and consent

after you join the study, you will read and sign an informed consent form that explains the purpose of the trial and what is expected of you.

2 baseline assessments

you will undergo a series of baseline evaluations that include a medical history review, physical and neurological examinations, vital sign measurements, electrocardiogram (ecg), laboratory tests, and documentation of your seizure frequency.

these assessments establish your starting point before any study medication is given.

3 first dose – single ascending dose (sad)

you will receive a one‑time intrathecal injection of ion337. the dose is selected by the study protocol and may increase for different participants as part of the dose‑escalation design.

the injection is administered into the space surrounding the spinal cord (intrathecal route).

4 post‑dose observation (sad)

following the single dose, you will be monitored closely for safety. this includes regular checks of vital signs, laboratory values, and any adverse events for a period of up to 28 days.

you may have scheduled clinic visits or telephone contacts to report any side effects or changes in your condition.

5 evaluation for multiple dose eligibility

the study team will review the safety data collected after the single dose. if the data meet predefined safety criteria, you may be offered entry into the multiple ascending dose (mad) part of the trial.

6 multiple dose phase – repeated intrathecal injections (mad)

in the mad phase you will receive repeated intrathecal injections of ion337. the dose may be increased stepwise according to the protocol.

injections are given at regular intervals (for example, once every week) for a defined treatment period, which is outlined in the study schedule.

7 ongoing safety and efficacy monitoring (mad)

throughout the multiple dose period you will continue to have regular clinic visits for safety assessments, laboratory tests, vital sign checks, and seizure frequency recording.

the study will also collect blood and cerebrospinal fluid samples to measure the concentration of ion337 (pharmacokinetic monitoring).

8 final study visit

at the end of the treatment period you will undergo a final set of examinations similar to the baseline assessments.

all study data will be compiled, and you will be informed that your participation in the trial is complete.

Who Can Join the Study?

A parent or legal guardian (authorized representative) must be willing to give permission (informed consent) and attend all study visits.
The child must be between 2 and 12 years old when the permission is given.
The child must have a confirmed diagnosis of Dravet Syndrome (DS) that meets the standards set by the International League Against Epilepsy (ILAE) and is accepted by the study’s review group (ESCI).
A genetic test must show a disease‑causing change (a pathogenic or likely pathogenic SCN1A variant) in the SCN1A gene.
The child must be taking at least one anti‑seizure medicine (concomitant ASM) and have been on the same dose for at least 4 weeks before joining the study.
All other epilepsy treatments (such as a special high‑fat diet called the ketogenic diet or a device called a vagus nerve stimulator) and any other medications (for behavior, sleep, vitamins, etc.) must also have been unchanged for at least 4 weeks. If a vagus nerve stimulator is used, it must have been implanted at least 6 months ago.
The child must have experienced the required number of major motor seizures (large, noticeable seizures that involve movement) during the initial screening phase (Screening Period).

Who Cannot Join the Study?

Having a known brain or spinal disease that could make a lumbar puncture (LP) unsafe or affect the flow of cerebrospinal fluid (CSF), the fluid that surrounds the brain and spinal cord.
Having a pathogenic (harmful) or likely harmful change in another gene that is known to cause epilepsy (a seizure disorder).
Having a gain‑of‑function variant in the SCN1A gene, which means the gene works too strongly and can increase seizure risk.
Currently taking an anti‑seizure medicine (ASM) that works mainly as a sodium channel blocker as a regular (maintenance) treatment.
Having had previous brain surgery, such as a corpus callosotomy (cutting the connection between the two halves of the brain), implantation of a device for deep brain stimulation (a device that sends electrical signals to the brain), or any other palliative brain surgery done to try to reduce seizures.

Where you can join this trial?

Verified and Recommended Sites

No sites found in this category

Verified Sites

Site Name	City	Country	Status
Katholieke Universiteit te Leuven	Leuven	Belgium
Unidade Local De Saúde De Santa Maria, E.P.E.	Lisbon	Portugal

Other Sites

Site Name	City	Country
Charite Universitaetsmedizin Berlin KöR	Berlin	Germany
Aiuhainsme Pyzqmfgt Hjjqssxg Do Mtlfptxbv	Marseille	France
Uzcbgpleck Ov Awjjesv	Edegem	Belgium
Gsdiaf Uqahvhvoov Fnokgesbg	Frankfurt	Germany
Cjhhse Hfxdnyeonz E Usiidkjskscal Dj Cdptwqq Eodvtq	Coimbra	Portugal

Trial status

Country	Status	Recruitment Start
Belgium	Not yet recruiting	01.07.2026
France	Not yet recruiting	01.07.2026
Germany	Not yet recruiting	01.07.2026
Portugal	Not yet recruiting	01.07.2026

Trial locations

ION337 is a new experimental drug being studied for people with Dravet syndrome. In this trial the medicine is given directly into the fluid surrounding the spinal cord (intrathecal injection). The study is looking at how safe the drug is, how well patients can tolerate it, and how the body absorbs and responds to it. Researchers will give participants either a single dose or increasing doses over time to learn about its effects.

Dravet Syndrome – Dravet Syndrome is a rare genetic brain disorder that begins in early childhood. It is marked by frequent seizures that often start with a high fever. As the child grows, the seizures become more varied and can occur without fever. The condition also leads to delays in learning and development. Over time, movement and behavior challenges may appear and the pattern of seizures can change.

Trial ID:

2025-523835-20-00

Protocol code:

ION337-CS1

Trial Phase:

Phase I and Phase II (Integrated) – First administration to humans

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Safety and Tolerability of Intrathecal ION337 in Patients with Dravet Syndrome

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?