Vertex Pharmaceuticals is advancing VX-433, an oral investigational compound, into a first-in-human Phase I clinical trial targeting narcolepsy type 1, a rare sleep disorder driven by the loss of orexin-producing neurons. The trial, registered as NCT07584434, enrolled up to 118 healthy adult volunteers and is scheduled to run through March 2027.
The study follows a three-part sequential structure. Parts A and B are randomized, quadruple-masked, and placebo-controlled, evaluating single ascending doses and multiple ascending doses of VX-433, respectively. Part C is open-label and tests whether VX-433 alters the plasma exposure of two established probe drugs: midazolam, an oral CYP3A4 substrate, and bupropion along with its active metabolite hydroxybupropion, which are CYP2B6 substrates.
Primary objectives across the three parts include characterizing the adverse event and serious adverse event profile of VX-433 under both SAD and MAD conditions, and quantifying changes in the maximum observed plasma concentration and area under the concentration-time curve of the probe drugs in the presence and absence of VX-433. Secondary measures cover VX-433 pharmacokinetics in detail, including plasma half-life, renal clearance, urinary excretion, and peak and total drug exposure across both single and multiple dosing periods. The DDI cohort also carries safety monitoring as a secondary endpoint, with follow-up extending to day 29 of that arm.
According to the trial record, participants must be adults aged 18 to 55 with a body mass index between 18 and 30 kilograms per square meter and a total body weight above 50 kilograms. The trial was registered on May 6, 2026, with a planned start date of May 12, 2026, and a primary completion date of March 5, 2027.
The trial context
Narcolepsy type 1 is caused by the selective, immune-mediated destruction of hypothalamic neurons that produce orexin, a neuropeptide that stabilizes wakefulness and suppresses rapid eye movement sleep. The resulting orexin deficiency produces the hallmark features of the condition: excessive daytime sleepiness, cataplexy triggered by emotion, disrupted nocturnal sleep, and hypnagogic hallucinations. Existing pharmacological management relies largely on symptom suppression through stimulants, sodium oxybate, and pitolisant, none of which restore the underlying orexinergic signaling deficit.
The mechanism of action of VX-433 has not been disclosed in any publicly available source. However, the indication and the oral small-molecule formulation are consistent with the approach being pursued by several other developers in this space: selective agonism of the orexin receptor 2, which is the receptor subtype most directly implicated in wakefulness promotion and cataplexy suppression. This mechanistic inference cannot be attributed to VX-433 without a citable source, and other wake-promoting targets cannot be excluded.