A Phase 4 interventional study of Metaxalone 640 mg and Metaxalone 800 MG in Healthy Participants, sponsored by Primus Pharmaceuticals. Recruiting at 1 site in United States. Open to participants aged 18 Years to 55 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-11-05.
Sponsored by Primus Pharmaceuticals · Phase 4, Interventional, and Basic science
Health participants take a single dose, perform testing, washout for one week, take a single dose of different formulation, and perform testing for comparison of the 2 doses.
Healthy participants will take one dose of a drug after eating a meal. When the drug is at the highest level in their blood, testing for drowsiness and the risk of falling will take place. Brain wave monitoring known as an EEG will take place throughout the testing. Participants will take a second dose of the drug with the same testing one week later.
Primus Pharmaceuticals is the lead sponsor of 20 studies on the registry; 3 are open to participants now.
Of its 6 completed or terminated interventional studies of FDA-regulated products, 5 (83%) have results posted.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
One dose administered after a standard meal with testing Baseline dose to time of maximum concentration (Tmax)
Drug: Metaxalone 640 mg
One dose administered after a standard meal with testing Baseline dose to time of maximum concentration (Tmax)
Drug: Metaxalone 800 MG
Dose micronized 640 mg
Also known as: m640
The dose is 800 mg
Also known as: Skelaxin
Change from baseline to approximately 4 hours post-dose, in mean reaction time to a stimulus as measured in milliseconds by the Reaction Time Test (RTT)
Measures the time between a visual stimulus and response, measured in milliseconds
Time frame: Baseline dose to four (4 ) hours post-dose
Change from baseline to approximately 4 hours post-dose of delayed response exceeding a predefined threshold >300 ms as measured by the Reaction Time Test (RTT)
measures the time between a visual stimulus and response, measured in milliseconds
Time frame: Baseline dose to approximately 4 hours post-dose
Plan to share: No — No plan for publication at this time.
No publications or documents are linked to this record.
Started Oct 2026 (actual). Primary completion is estimated for Jan 2027, 3 months after the start.
Start moved once since we started tracking on Sep 25, 2026: Sep 2026 → Oct 2026, on Nov 5, 2026.
Earlier changes are on the record history on ClinicalTrials.gov ↗
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
Eligibility is decided by the study team. Share this record with your doctor or contact the team directly.
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Studies of the drug tested here: Metaxalone
Primus Pharmaceuticals