This page shows what was measured, who it was measured in, and what that does not settle.
What Viltolarsen does in the body
Duchenne Muscular Dystrophy (exon 53 skipping)
Viltolarsen is a shorter version of the same idea as golodirsen: cover exon 53 so the cell leaves it out and the reading frame lines up again. The 16-boy study reported dystrophin at about six percent of normal, several times higher than the other exon 53 drug. When a proper randomised trial of 77 boys then measured how quickly they could stand up from the floor, the treated and placebo groups both improved and there was no difference between them.
What happened in people
Dystrophin 0.6 percent to 4.2 percent of normal by filamin-C-normalised mass spectrometry
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The recorded finding that sits closest to something a person would notice. Written into the record, not signed off, and it carries no population or interval.
VILTEPSO (viltolarsen) US prescribing information, DailyMed (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123) · a recorded source, not a stored snapshot
NS Pharma, preliminary results of the RACER53 phase 3 study, 27 May 2024 (https://www.nspharma.com/ns-pharma-shares-preliminary-results-of-viltolarsen-ns-065… · a recorded source, not a stored snapshot
The limit that matters most
That the timed-function gains against 65 natural-history controls were a treatment effect; the randomised trial did not reproduce them
Where it acts
Skeletal muscle fibre nucleus
Kind of result
A number that stands in for health
Supervision
Professional supervision is normally required. It is a prescription or clinician-administered medicine where it is approved.
What the registries record it as
The substance registry classes this as nucleicacid.
FDA substance registry · SXA7YP6EKX · read 2026-08-29
Where each sentence above came from
No recorded sentence describes the change this makes in a way that stands on its own. The page opens with what it is taken for instead, and the recorded explanation follows below.
Shown as the opening line on this page.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 102 words.
Words this page uses
Four words worth knowing first
Chosen from what this page shows, with each one explained before the word it depends on.
Protein
A protein is a folded chain your body builds to do a specific job.
A picture of it, and where the picture fails
A protein is like a tool bent into one shape for one task.
Where that stops being true. A tool keeps its shape. A protein can change shape and stop working.
What people get wrong. Protein in food and a protein in the body are related but not the same thing.
A polymer of amino acids folded into a defined structure that determines its function.
Gene
A gene is a stretch of instructions for building one protein.
A picture of it, and where the picture fails
A gene is like one page of a building plan.
Where that stops being true. A page is read the same way every time. A gene can be read more or less often.
What people get wrong. Having a gene is often read as having a trait. Whether it is used matters as much.
A segment of DNA that encodes a functional product, usually a protein.
Messenger RNA
Messenger RNA is a working copy of one gene, carried to where proteins are built.
A picture of it, and where the picture fails
It is like a photocopy of one plan page, taken to the workshop.
Where that stops being true. A photocopy lasts. This copy is destroyed soon after use, on purpose.
What people get wrong. It is often thought to change the gene. It is a copy, and it does not alter the original.
A single-stranded transcript of a gene that ribosomes translate into a protein.
Small interfering RNA
A small interfering RNA is a short piece that makes a cell destroy one working copy.
A picture of it, and where the picture fails
It is like a note telling the workshop to shred one plan page.
Where that stops being true. A note is read once. This keeps working for months after one injection.
What people get wrong. It is often described as gene editing. It leaves the gene untouched.
A short double-stranded RNA that directs the RNA-induced silencing complex to cleave a complementary transcript.
What happened in people◇Read from sources, not yet reviewed
What happened in people
Each card is one study: the exact question it asked, who was in it, and whether it showed what it set out to show.
Safety, tolerability and de novo dystrophin production by western blot in biceps at week 25
✓ The study showed what it set out to show
Who was studied
NS-065/NCNP-01 Study 1 (NCT02740972)
How many people
16
Study design
Phase 2
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
p=0.01 for dystrophin change at 80 mg/kg weekly
Repeated elsewhere
Failed to Replicate
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Timed-function comparisons in this study used 65 external natural-history controls rather than a randomised placebo arm
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Intravenous infusion of an uncharged phosphorodiamidate morpholino oligomer in saline
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
VILTEPSO (viltolarsen) US prescribing information, DailyMed (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123) · a recorded source, not a stored snapshot
NS Pharma, preliminary results of the RACER53 phase 3 study, 27 May 2024 (https://www.nspharma.com/ns-pharma-shares-preliminary-results-of-viltolarsen-ns-065… · a recorded source, not a stored snapshot
Time to stand from supine at week 48 versus placebo
✗ The study did not show it
Who was studied
RACER53 (NCT04060199)
How many people
77
Study design
Phase 3
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
No statistically significant difference between arms
Repeated elsewhere
Failed to Replicate
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. No limitation is recorded for this study.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Intravenous infusion of an uncharged phosphorodiamidate morpholino oligomer in saline
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
VILTEPSO (viltolarsen) US prescribing information, DailyMed (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123) · a recorded source, not a stored snapshot
NS Pharma, preliminary results of the RACER53 phase 3 study, 27 May 2024 (https://www.nspharma.com/ns-pharma-shares-preliminary-results-of-viltolarsen-ns-065… · a recorded source, not a stored snapshot
RNAWiki holds 2 written-up human studies for this substance, each with the question it asked.
How we know it
Each card names the study, the number of people and what the study set out to measure.
What this does not prove
These summaries were written by a person and have not been signed off as reviewed claims.
Why it matters
A study that failed is as informative as one that worked, and both are here.
What we still do not know
No reviewed claim exists, so no exact population, effect size or interval is published yet.
What it changes in the body◇Read from sources, not yet reviewed
The path through the body
From what a person takes to what changes. A solid line is a step measured in people. A dashed line is a step nobody has measured that way.
Start
Viltolarsen
What a person takes: Intravenous infusion of an uncharged phosphorodiamidate morpholino oligomer in saline.
The measurement behind this step
Single-dose vials of 250 mg in 5 mL, diluted into saline and infused weekly over about 60 minutes. No lipid carrier, no ligand, no chemical modification for muscle targeting.
Getting in
Weekly intravenous infusion in saline
Given into a vein once a week as a simple saline solution.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Uncharged 21-mer PMO supplied in 0.9 percent sodium chloride, infused over about an hour. Rapid renal elimination; low fractional muscle uptake.
VILTEPSO (viltolarsen) US prescribing information, DailyMed (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123) · a recorded source, not a stored snapshot
NS Pharma, preliminary results of the RACER53 phase 3 study, 27 May 2024 (https://www.nspharma.com/ns-pharma-shares-preliminary-results-of-viltolarsen-ns-065… · a recorded source, not a stored snapshot
Reaching the cell
Uptake into muscle fibre nuclei
Part of the dose enters muscle cells and reaches the nucleus.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Neutral backbone gives nuclease stability but no charge-driven cell-surface protein binding; uptake is thought to be aided by dystrophic membrane fragility.
VILTEPSO (viltolarsen) US prescribing information, DailyMed (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123) · a recorded source, not a stored snapshot
NS Pharma, preliminary results of the RACER53 phase 3 study, 27 May 2024 (https://www.nspharma.com/ns-pharma-shares-preliminary-results-of-viltolarsen-ns-065… · a recorded source, not a stored snapshot
What it acts on
Hybridising to a 21-nucleotide site in exon 53
It pairs with a stretch inside exon 53 and hides it from the splicing machinery.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
The 21-mer covers the same region as the 25-mer golodirsen minus five bases at the 5-prime end, occluding exonic splicing enhancer elements required for exon definition.
VILTEPSO (viltolarsen) US prescribing information, DailyMed (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123) · a recorded source, not a stored snapshot
NS Pharma, preliminary results of the RACER53 phase 3 study, 27 May 2024 (https://www.nspharma.com/ns-pharma-shares-preliminary-results-of-viltolarsen-ns-065… · a recorded source, not a stored snapshot
The change it makes
Exon 53 is skipped and the reading frame is restored
The exons on either side are joined and the instructions line up again.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
Exclusion of exon 53 produces an in-frame transcript in patients with deletions such as 52, 45-52 or 48-52, allowing translation through to the C-terminal domain.
VILTEPSO (viltolarsen) US prescribing information, DailyMed (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123) · a recorded source, not a stored snapshot
NS Pharma, preliminary results of the RACER53 phase 3 study, 27 May 2024 (https://www.nspharma.com/ns-pharma-shares-preliminary-results-of-viltolarsen-ns-065… · a recorded source, not a stored snapshot
What that does for a person
Truncated dystrophin at the sarcolemma, 4 to 6 percent of normal
Shortened dystrophin appears at the muscle membrane at a few percent of normal, depending which assay you use.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Western blot normalised to myosin heavy chain gives 5.9 percent; mass spectrometry normalised to filamin C gives 4.2 percent. Neither corresponded to a randomised functional benefit in RACER53.
VILTEPSO (viltolarsen) US prescribing information, DailyMed (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123) · a recorded source, not a stored snapshot
NS Pharma, preliminary results of the RACER53 phase 3 study, 27 May 2024 (https://www.nspharma.com/ns-pharma-shares-preliminary-results-of-viltolarsen-ns-065… · a recorded source, not a stored snapshot
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 5 steps from taking it to an effect in a person.
How we know it
Each step names the study behind it in the technical detail beside it.
What this does not prove
A change inside the body is a reason to look. It is not a result in a person.
Why it matters
A reader can see exactly where the chain stops being measured in people.
What we still do not know
No reviewed claim binds any of these steps to a named population.
What is missing or unclear◇Read from sources, not yet reviewed
Were people like you studied?
RNAWiki cannot tell whether a study fits you. It can show who was in it, and where the result stops carrying.
Who was studied
People similar to this profile were included.
Boys aged four and above with an exon-53-amenable DMD deletion, by weekly intravenous infusion, on a stable corticosteroid regimen.
Who is missing from the studies
Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What the label states about particular groups
On pediatric, the label states: “VILTEPSO is indicated for the treatment of DMD in patients who have a confirmed mutation of the DMD gene that is amenable to exon 53 skipping, including pediatric patients [see Clinical Studies ( 14 )].”
US prescribing information · 1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123 · read 2026-08-30
On older people, the label states: “DMD is largely a disease of children and young adults; therefore, there is no geriatric experience with VILTEPSO.”
US prescribing information · 1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123 · read 2026-08-30
On people who are pregnant, the label states: “Risk Summary There are no human or animal data available to assess the use of VILTEPSO during pregnancy.”
US prescribing information · 1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123 · read 2026-08-30
On people who are breastfeeding, the label states: “Risk Summary There are no human or animal data to assess the effect of VILTEPSO on milk production, the presence of viltolarsen in milk, or the effects of VILTEPSO on the breastfed infant.”
US prescribing information · 1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123 · read 2026-08-30
Where the result stopped carrying
RACER53 found no significant difference in time to stand from supine, because the placebo arm improved as well
The two assays used in the approval study disagreed by more than a third on the median change
This is a scope explorer, not a diagnosis engine.
It shows who was studied so you can see whether people similar to you were included.
RNAWiki cannot tell whether a study fits you. It can show who was in it.
What it would be like to take◇Read from sources, not yet reviewed
Why it might seem to do nothing
A real effect and a noticed effect are different things. These are the recorded reasons the two come apart.
It was studied in different people
The people in the studies were not much like the reader.
On this record: Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
The evidence may simply be wrong
Small early studies often do not hold up.
On this record: RNAWiki has not yet published a reviewed conclusion for this use.
Other reasons RNAWiki checked and found nothing for (11)
It was studied for a different goal
The studies measured something else entirely. Nothing in this record points to this reason.
A different form was studied
The studied form is not the form on the shelf. Nothing in this record points to this reason.
There was nothing to correct
Where a level is already normal, topping it up may change nothing. Nothing in this record points to this reason.
Something else had to happen too
In the studies it was paired with training, a diet or another treatment. Nothing in this record points to this reason.
The change is too small to feel
A real change can still sit below what a person notices. Nothing in this record points to this reason.
Day-to-day swing hides it
Sleep, food, stress and time of day move most numbers more than this would. Nothing in this record points to this reason.
Not enough time yet
The studies ran longer than the person has waited. Nothing in this record points to this reason.
It was not taken as studied
Missed days change the result, and studies count them. Nothing in this record points to this reason.
Something else changed at the same time
Two changes at once cannot be told apart afterwards. Nothing in this record points to this reason.
The product may not be what it says
Contents of a sold product are not always what the label states. Nothing in this record points to this reason.
No recorded reason
RNAWiki has nothing stored that would explain it. Nothing in this record points to this reason.
None of these is a reason to take more. Taking more is not a step this page ever suggests.
What it would be like to take◇Read from sources, not yet reviewed
What taking it involves
The recorded facts about getting hold of it and using it. Nothing here is a suggestion about what you should do.
How it is supplied
Not established
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Intravenous infusion of an uncharged phosphorodiamidate morpholino oligomer in saline
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form and route recorded on this substance.
No source is stored against this line.
Who oversees it
Professional supervision is normally required. It is a prescription or clinician-administered medicine where it is approved.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
The identity record classes it as ASO (Antisense Oligonucleotide).
No source is stored against this line.
What is in the pack
Single-dose vials of 250 mg in 5 mL, diluted into saline and infused weekly over about 60 minutes. No lipid carrier, no ligand, no chemical modification for muscle targeting.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on how this is sold and what that means for what is in the pack.
No source is stored against this line.
Where it is registered
Regulatory records are listed in the technical disclosure at the foot of this page.
# Counted from records
Where this came from
A count of rows RNAWiki holds. It describes our records, not your body.
Register entries are stored per jurisdiction and shown with their dates.
No source is stored against this line.
Why people stop
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No record of why people stopped taking it is stored for this substance.
No source is stored against this line.
What it would be like to take◇Read from sources, not yet reviewed
What can go wrong
Sorted by where each line came from. A regulator's label and a report somebody sent in are not the same kind of fact.
·Worth asking a clinician aboutWritten into the record from the studies named on this page
Most common adverse reactions at 15 percent or more were upper respiratory tract infection, injection site reaction, cough and pyrexia. Renal toxicity is a class warning based on nonclinical PMO findings and is monitored. No participant discontinued RACER53 for adverse events.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
Where this came from
VILTEPSO (viltolarsen) US prescribing information, DailyMed (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123) · a recorded source, not a stored snapshot
NS Pharma, preliminary results of the RACER53 phase 3 study, 27 May 2024 (https://www.nspharma.com/ns-pharma-shares-preliminary-results-of-viltolarsen-ns-065… · a recorded source, not a stored snapshot
Over a long time. No completed tested study window is recorded, so long-term effects are not established by the registry record.
Groups the studies covered thinly. Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What is missing or unclear◇Read from sources, not yet reviewed
Does the exact form matter?
Evidence belongs to the exact thing that was tested. A different salt, a different mixture or a different preparation is a different question.
The form that was studied
Intravenous infusion of an uncharged phosphorodiamidate morpholino oligomer in saline
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form used in the studies cited on this page.
No source is stored against this line.
What is sold
No lipid carrier, no ligand, no chemical modification for muscle targeting.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on which forms are sold and how they compare.
No source is stored against this line.
What is recorded as being sold
1 product lists this as an active ingredient in the United States drug directory. 1 of them contain it and nothing else.
FDA National Drug Code directory · 73292-011 · read 2026-08-29
They are sold as injection, solution, taken intravenous.
FDA National Drug Code directory · 73292-011 · read 2026-08-29
1 published label names it as an active ingredient. 1 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · 1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123 · read 2026-08-29
Those labels are classed as human prescription drug.
US prescribing information · 1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123 · read 2026-08-29
Viltepso is intravenous at 3 DOSAGE FORMS AND STRENGTHS VILTEPSO is a clear and colorless solution available as follows: Injection: 250 mg/5 mL (50 mg/mL) solution in a single-dose vial Injection: 250 mg/5 mL (50 mg/mL) in a single-dose vial ( 3 ), recorded as fda label in effect 2025-07-16 in the United States.
US prescribing information · 1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123 · read 2026-08-30
Evidence carries across two names for one substance. It does not carry across a salt, a mirror form or a mixture.
What it would be like to take◇Read from sources, not yet reviewed
What you could measure
This one is decided with a clinician, so this section holds questions to ask rather than a plan to run.
Self-experiment planning is not offered for a prescription or clinician-supervised medicine. The questions below are for a clinician or pharmacist.
Questions worth asking
Which of the trials of Viltolarsen studied people like me?
What was measured, and for how long?
Was the result a laboratory value or a health outcome?
What would we watch for, and when would we stop?
Tracking can show whether something changed for you. It cannot show what caused it.
RNAWiki records evidence. It does not say whether this substance is right for you.
What is missing or unclear◇Read from sources, not yet reviewed
Claims that go past the evidence
Things said about this substance that sound reasonable, and the exact step that is missing between the evidence and the claim.
✗Goes past the evidence
That the timed-function gains against 65 natural-history controls were a treatment effect; the randomised trial did not reproduce them
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That a higher reported dystrophin percentage than golodirsen means a more effective drug
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
What is missing or unclear◇Read from sources, not yet reviewed
What nobody knows yet
Open questions, each with why it is open and what would close it.
How much did people take in the studies?
The sources RNAWiki checked hold nothing for this field.
Why it matters. A result belongs to an amount. Without the amount the result floats free.
What would answer it
A stored source that records it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing populations
Which groups were under-represented in the studies has not been recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing long-term data
No completed tested study window is recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
No reviewed conclusion
RNAWiki has not yet published a reviewed conclusion for this use.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing interaction studies
No interaction was found in the registers checked. Not finding one is not the same as showing there is none.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Formulation uncertainty
Several salts, forms or products of Viltolarsen are recorded. Results from one form may not transfer to another.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Mechanism not reviewed
No reviewed mechanism story exists for this substance.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
What happened in people◇Read from sources, not yet reviewed
Check any of this yourself
Every line above traced back to the study it came from. This is the technical layer, and the vocabulary changes here.
Every line above can be traced to the study named beside it. Follow the link and read it.
Dystrophin reached 5.9 percent of normal at week 25
In plain words
In eight boys on the approved dose, average dystrophin rose from 0.6 percent to 5.9 percent of normal after 24 weeks of treatment.
What was measured
Mean dystrophin 0.6 percent to 5.9 percent of normal, p=0.01, n=8
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Study 1 (NCT02740972) treated 16 boys, 8 at each of two doses. In the 80 mg/kg weekly group, western blot normalised to myosin heavy chain gave a mean of 0.6 percent (SD 0.8) at baseline and 5.9 percent (SD 4.5) at week 25, mean change 5.3 percent (SD 4.5), p=0.01, median change 3.8 percent. All patients increased over baseline.
Written into the record, not signed off as a reviewed claim
The second assay gave a lower number: 4.2 percent by mass spectrometry
In plain words
The same muscle samples, measured a different way, gave 4.2 percent instead of 5.9 percent, and the median was 1.9 percent rather than 3.8 percent.
What was measured
Mass spectrometry dystrophin 0.6 percent to 4.2 percent of normal, median change 1.9 percent
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Mass spectrometry normalised to filamin C gave a mean of 0.6 percent (SD 0.2) at baseline and 4.2 percent (SD 3.7) at week 25, change 3.7 percent (SD 3.8), nominal p=0.03 not adjusted for multiple comparisons, median change 1.9 percent. Reporting both is good practice, and the gap between them is the honest measure of how assay-dependent this endpoint is.
Source
VILTEPSO US prescribing information, section 14
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
caution
Review state
Written into the record, not signed off as a reviewed claim
RACER53 missed its primary endpoint because placebo improved too
In plain words
The randomised confirmatory trial of 77 boys measured how fast they could stand up from lying down. Treated boys got faster, and so did the placebo group, so there was no significant difference.
What was measured
Time to stand from supine at week 48: no statistically significant difference
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
RACER53 (NCT04060199) randomised 77 ambulatory boys to viltolarsen 80 mg/kg weekly or placebo for 48 weeks, with time to stand from supine as the primary endpoint. Preliminary results announced in May 2024 reported a trend of increased rising velocity in the treated group, matched by improvement in the placebo comparators, and no statistically significant difference between arms. Adverse events were mild or moderate and no participant withdrew for side effects.
Source
NS Pharma preliminary RACER53 results announcement, May 2024
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
contested
Review state
Written into the record, not signed off as a reviewed claim
Timed-function gains were measured against 65 historical controls, not a randomised arm
In plain words
The improvements in walking and standing reported in the approval study came from comparing treated boys with boys from old natural-history datasets, not with a placebo group.
What was measured
That the timed-function differences against natural-history controls represent a treatment effect
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The phase 2 study compared all 16 treated participants against 65 age-matched and treatment-matched natural-history controls, reporting improvements in time to stand from supine, 10-metre run/walk and 6-minute walk at week 25. External-control comparison in a disease with steep age-dependent trajectories is exactly the design that RACER53 was built to replace, and RACER53 found no separation.
Written into the record, not signed off as a reviewed claim
Two drugs, one exon, a sixfold gap in reported dystrophin, and neither changed function
In plain words
Viltolarsen reports about six times more dystrophin than golodirsen for the same exon. Both then failed their confirmatory functional trials, which undercuts the idea that the percentage is what matters.
What was measured
That percentage-of-normal dystrophin is a rank-ordered measure of exon-skipping drug potency
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Golodirsen reported 1.02 percent of normal by Sarepta western blot; viltolarsen reported 5.9 percent by myosin-heavy-chain-normalised western blot. If dystrophin percentage were the operative variable, a sixfold difference should have produced separable functional outcomes. RACER53 and ESSENCE both missed their primary endpoints. That result is informative about the surrogate itself, not only about either drug.
Source
VILTEPSO and VYONDYS 53 prescribing information, section 14; RACER53 and ESSENCE topline results
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
contested
Review state
Written into the record, not signed off as a reviewed claim
Where else this substance is registered
FDA substance identifier (UNII)
SXA7YP6EKX
RxNorm concept
2389844
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Trial roles classified for highlighted evidence
No registered study is classified as testing this substance.
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The identity record classes it as ASO (Antisense Oligonucleotide).
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What is missing or unclear◇Read from sources, not yet reviewed
How this medicine reached us
Kept near the foot of the page. A historical event moves up only when it changes something about this substance today.
What the approval register records
1 approved application covers products containing this substance. The earliest was NDA212154, approved 20200812 to NIPPON SHINYAKU.
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The older medicine-wide conclusion held in this record
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A 21-mer morpholino for exon 53 that produced the highest reported dystrophin of any approved exon-skipping drug, 5.9 percent of normal in 16 boys, and then failed its randomised confirmatory trial on time to stand from supine.
Recorded evidence blocks (4)
Q1
On the Viltolarsen label: indicated for what?
"VILTEPSO is indicated for the treatment of Duchenne muscular dystrophy (DMD) in patients who have a confirmed mutation of the DMD gene that is amenable to exon 53 skipping. This indication is approved under accelerated approval based on an increase in dystrophin production in skeletal muscle observed in patients…": indications and usage on Viltolarsen's label. DailyMed label · 1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123 · 2025-07-16
Q2
5 registered trials of Viltolarsen — at which phases?
In Vitro Drug Interaction Studies Viltolarsen did not inhibit CYP3A4/5, CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, UGT1A1, or UGT2B7.
pharmacokinetics
Viltolarsen did not induce CYP1A2, CYP2B6, or CYP3A4.
pharmacokinetics
Viltolarsen is not metabolized by CYP enzymes and is not a substrate of transporters BCRP, BSEP, MDR1, OAT1, OAT3, OCT1, OCT2, MATE1, or MATE2-K.
pharmacokinetics
Viltolarsen did not inhibit the transporters tested (OATP1B1, OATP1B3, OAT3, BCRP, MDR1, BSEP, OAT1, OCT1, OCT2, MATE1, and MATE2-K).
clinical_pharmacology
In Vitro Drug Interaction Studies Viltolarsen did not inhibit CYP3A4/5, CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, UGT1A1, or UGT2B7.
clinical_pharmacology
Viltolarsen did not induce CYP1A2, CYP2B6, or CYP3A4.
2 more recorded rows
Interaction statementclinical_pharmacology
Viltolarsen is not metabolized by CYP enzymes and is not a substrate of transporters BCRP, BSEP, MDR1, OAT1, OAT3, OCT1, OCT2, MATE1, or MATE2-K.
Interaction statementclinical_pharmacology
Viltolarsen did not inhibit the transporters tested (OATP1B1, OATP1B3, OAT3, BCRP, MDR1, BSEP, OAT1, OCT1, OCT2, MATE1, and MATE2-K).
ChEMBL 37 — CC BY-SA 3.0 Unported · ChEMBL ATC CC BY-SA · ClinicalTrials.gov — US Government work · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — US Government work
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