A Phase 4 interventional study of JZP258 in Narcolepsy, sponsored by Jazz Pharmaceuticals. Completed at 43 sites in 5 countries. Open to participants aged 18 Years to 70 Years. Per ClinicalTrials.gov, last updated 2026-04-24.
Sponsored by Jazz Pharmaceuticals · Phase 4, Interventional, and Treatment
The aim of this study is to quantify the change in blood pressure when participants with narcolepsy treated with high-sodium oxybate are transitioned to Xywav, a low-sodium oxybate. The results of this study may provide health care providers (HCPs), patients, and payers with important new information regarding BP changes related to differences in sodium content between available oxybates for the treatment of narcolepsy.
157 studies on the registry are indexed under Narcolepsy; 37 are open to participants now.
This study's enrollment of 155 is above the median of 78 across 114 interventional studies indexed under Narcolepsy.
Browse Narcolepsy studies →Jazz Pharmaceuticals is the lead sponsor of 173 studies on the registry; 18 are open to participants now.
Of its 42 completed or terminated interventional studies of FDA-regulated products, 32 (76%) have results posted.
Counted across the registry records on this site, refreshed daily.
Key Inclusion Criteria:
Key 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.
The American Psychiatric Association’s manual of mental health diagnoses. DSM-5 (2013, revised as DSM-5-TR in 2022) replaced DSM-IV, and some studies still name the older edition. “Meets DSM criteria for …” means diagnosed by that edition’s diagnostic criteria, usually by a clinician in an interview.
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
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.
DSM diagnostic criteria
The American Psychiatric Association’s manual of mental health diagnoses. DSM-5 (2013, revised as DSM-5-TR in 2022) replaced DSM-IV, and some studies still name the older edition. “Meets DSM criteria for …” means diagnosed by that edition’s diagnostic criteria, usually by a clinician in an interview.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Childbearing potential
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
ECG (electrocardiogram)
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Eligible participants will be switched, on a gram-for-gram basis, from their prescribed twice-nightly high-sodium oxybate (such as xyrem) to Xywav. Participants who, in the opinion of the investigator, require an adjustment to their Xywav dosing, can increase or decrease their dose by 1.5 grams per night as long as the participant's total nightly dose is between 6 to 9 grams per night.
Drug: JZP258
0.5 g/ml calcium, magnesium, potassium, and sodium oxybates oral solution
Also known as: Xywav
Change From Baseline to End of Treatment (EOT) Visit on the 24-hour Average Systolic Blood Pressure (SBP) in mmHg
Time frame: Baseline (Screening) and End of Treatment (EOT) Visit, up to 6 weeks
Change From Baseline to EOT Visit on the Daytime Average SBP in mmHg
Time frame: Baseline (Screening) and End of Treatment (EOT) Visit, up to 6 weeks
Change From Baseline to EOT Visit on the Seated Resting Average SBP in mmHg
Time frame: Baseline (Screening) and End of Treatment (EOT) Visit, up to 6 weeks
Change From Baseline to EOT Visit on the Nighttime Average SBP in mmHg
Time frame: Baseline (Screening) and End of Treatment (EOT) Visit, up to 6 weeks
A total of 155 participants is in the enrolled analysis set. The enrolled analysis set includes all participants who provided informed consent for this study.
| Milestone | JZP258 |
|---|---|
| Started | 155 |
| Completed | 67 |
| Not completed | 88 |
| Withdrew: Screen failure | 88 |
| Milestone | JZP258 |
|---|---|
| Started | 67 |
| Completed | 60 |
| Not completed | 7 |
| Withdrew: Lost to follow-up | 1 |
| Withdrew: Protocol violation | 4 |
| Withdrew: Withdrawal by subject | 1 |
| Withdrew: Sponsor decision | 1 |
| mmHg | JZP258 |
|---|---|
| Change From Baseline to End of Treatment (EOT) Visit on the 24-hour Average Systolic Blood Pressure (SBP) in mmHg | -4.14 ± 1.348 |
| mmHg | JZP258 |
|---|---|
| Change From Baseline to EOT Visit on the Daytime Average SBP in mmHg | -5.08 ± 1.344 |
| mmHg | JZP258 |
|---|---|
| Change From Baseline to EOT Visit on the Seated Resting Average SBP in mmHg | -9.16 ± 1.337 |
| mmHg | JZP258 |
|---|---|
| Change From Baseline to EOT Visit on the Nighttime Average SBP in mmHg | -1.95 ± 1.679 |
Collected over Baseline (Screening) up to 11 weeks. Non-serious events are listed at a 2% frequency threshold.
| Group | Deaths | Serious | Other |
|---|---|---|---|
| JZP258-406 Screening Period | 0/155 (0%) | 0/155 (0%) | — |
| JZP258-406 Treatment Period | 0/67 (0%) | 1/67 (1.5%) | 11/67 (16.4%) |
| Event | JZP258-406 Screening Period | JZP258-406 Treatment Period |
|---|---|---|
| HospitalisationSurgical and medical procedures | 0/155 | 1/67 |
| Event | JZP258-406 Screening Period | JZP258-406 Treatment Period |
|---|---|---|
| Upper respiratory tract infectionInfections and infestations | — | 3/67 |
| NauseaGastrointestinal disorders | — | 2/67 |
| VomitingGastrointestinal disorders | — | 2/67 |
| GastroenteritisInfections and infestations | — | 2/67 |
| DysgeusiaNervous system disorders | — | 2/67 |
A total of 67 participants are included in the safety analysis set. The safety analysis set includes all participants who took/received at least 1 dose of study intervention.
| Age, Categorical(Participants) | JZP258 |
|---|---|
| <=18 years | 0 |
| Between 18 and 65 years | 63 |
| >=65 years | 4 |
| Sex: Female, Male(Participants) | JZP258 |
|---|---|
| Female | 34 |
| Male | 33 |
| Ethnicity (NIH/OMB)(Participants) | JZP258 |
|---|---|
| Hispanic or Latino | 5 |
| Not Hispanic or Latino | 60 |
| Unknown or Not Reported | 2 |
| Race (NIH/OMB)(Participants) | JZP258 |
|---|---|
| American Indian or Alaska Native | 0 |
| Asian | 1 |
| Native Hawaiian or Other Pacific Islander | 0 |
| Black or African American | 3 |
| White | 57 |
| More than one race | 1 |
| Unknown or Not Reported | 5 |
PDFs hosted by the registry, ClinicalTrials.gov.
Plan to share: Yes — In accordance with ICMJE requirements, Jazz Pharmaceuticals may provide qualified external researchers access to individual participant data (IPD) and clinical trial data that underlie the results of this trial upon request. Qualified researchers can submit a request on https://www.jazzpharma.com/science/clinical-trial-data-sharing/ as outlined. Jazz Pharmaceuticals reserves the right not to consider a request. For inquiries about Jazz's data sharing policy contact clinicaldatasharing@jazzpharma.com.
Data sharing details ↗ · www.jazzpharma.com
This study is completed, as verified in Apr 2026. You cannot join it, but the record below documents what was studied.
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Studies of the drug tested here: JZP258