KL1333 (napazimone)
An investigational treatment for Primary mitochondrial disease (mitochondrial DNA).
The same compound appears under different names depending on the context. Here is how to identify KL1333 (napazimone) wherever you encounter it, plus the key facts at a glance.
- Generic name
- KL1333 (napazimone)
- Development codes
- KL1333, napazimone
- Drug class
- NAD+ modulator (investigational)
- Manufacturer
- Pharming
- How it's taken
- In the Phase 2 trial, KL1333 or placebo is taken by mouth twice a day, with the dose adjusted during the study (a flexible-dose design).
An oral drug taken twice a day, in a Phase 2 trial for adults with primary mitochondrial disease caused by mitochondrial DNA changes, including MELAS, MIDD, Kearns-Sayre and MERRF. Not approved anywhere, and not being tested in children; the trial excludes Leigh syndrome.
How KL1333 (napazimone) works
NAD+ and NADH are helper molecules that mitochondria use at several steps of energy production. Pharming describes KL1333 as correcting the balance between them so that the remaining working mitochondria produce more energy. It does not correct the underlying gene fault.
Mechanism: Oral small molecule that its developer describes as a modulator of the NAD+/NADH balance, which mitochondria rely on to make energy
Side effects and safety
Safety results from the Phase 2 FALCON trial have not been published. The trial is placebo-controlled with a flexible dose, so side effects will be reported against placebo when it reads out after October 2027. Ask the study team what earlier studies showed before enrolling.
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking KL1333 (napazimone)
In the Phase 2 trial, KL1333 or placebo is taken by mouth twice a day, with the dose adjusted during the study (a flexible-dose design).
Clinical trial results
FALCON (NCT05650229) is a Phase 2, randomized, double-blind, placebo-controlled, adaptive trial that began in December 2022 and plans to enroll about 180 adults with a genetically confirmed mitochondrial DNA disease and chronic fatigue. The main outcomes are a fatigue questionnaire (PROMIS Fatigue) and the 30-second sit-to-stand test. Primary completion is expected in October 2027. Sites are in the United States, Australia and 9 European countries. An open-label extension (NCT07514338) lets participants continue on the drug.
Main registered trial: NCT05650229 on ClinicalTrials.gov. Check it for the current status, sites and contacts before asking about enrollment.
Development history
Pharming Technologies B.V. sponsors the FALCON Phase 2 trial, which began in December 2022, and the open-label extension that follows it.
Explore Primary mitochondrial disease (mitochondrial DNA) trials
Common questions about KL1333 (napazimone)
▸What is KL1333 (napazimone)?
An oral drug taken twice a day, in a Phase 2 trial for adults with primary mitochondrial disease caused by mitochondrial DNA changes, including MELAS, MIDD, Kearns-Sayre and MERRF. Not approved anywhere, and not being tested in children; the trial excludes Leigh syndrome.
▸How does KL1333 (napazimone) work?
NAD+ and NADH are helper molecules that mitochondria use at several steps of energy production. Pharming describes KL1333 as correcting the balance between them so that the remaining working mitochondria produce more energy. It does not correct the underlying gene fault.
▸What are the side effects of KL1333 (napazimone)?
Safety results from the Phase 2 FALCON trial have not been published. The trial is placebo-controlled with a flexible dose, so side effects will be reported against placebo when it reads out after October 2027. Ask the study team what earlier studies showed before enrolling.
▸How is KL1333 (napazimone) taken?
In the Phase 2 trial, KL1333 or placebo is taken by mouth twice a day, with the dose adjusted during the study (a flexible-dose design).
▸Is KL1333 (napazimone) FDA approved?
KL1333 (napazimone) is currently in phase 2 clinical trials for Primary mitochondrial disease (mitochondrial DNA). It has not yet received FDA approval.
▸Is KL1333 being tested for Leigh syndrome?
No. The FALCON trial enrolls adults with mitochondrial DNA diseases such as MELAS, Kearns-Sayre and MERRF who have chronic fatigue, and it specifically excludes Leigh syndrome from any gene, as well as NARP and LHON. Children are not eligible. Pharming has said topline results are expected in late 2027. [1]
▸Where is the KL1333 trial recruiting?
FALCON (NCT05650229) lists sites in the United States, Australia, Belgium, Czechia, Denmark, France, Germany, Italy, the Netherlands, Spain and the United Kingdom, and was recruiting as of September 2026. The ClinicalTrials.gov listing has the current sites. [1]
▸Is KL1333 FDA approved?
No. KL1333 is not FDA-approved and is not approved anywhere. It is in a Phase 2 trial called FALCON (NCT05650229), sponsored by Pharming, which began in December 2022 and plans to enroll about 180 adults with a genetically confirmed mitochondrial DNA disease and chronic fatigue. Primary completion is expected in October 2027, and an open-label extension (NCT07514338) lets participants continue on the drug. [1][2]
▸How does KL1333 work?
KL1333 is an oral drug taken by mouth twice a day, with the dose adjusted during the FALCON trial in a flexible-dose design. Pharming describes it as correcting the balance between NAD+ and NADH, helper molecules that mitochondria use at several steps of energy production, so the remaining working mitochondria produce more energy. It does not correct the underlying gene fault. [1]
Sources and references
Every factual claim on this page is drawn from the public sources listed below. Click any reference to open the original document.
- ClinicalTrials.gov. Efficacy of KL1333 in Adult Patients With Primary Mitochondrial Disease. https://clinicaltrials.gov/study/NCT05650229
- ClinicalTrials.gov. KL1333 open-label extension study. https://clinicaltrials.gov/study/NCT07514338