Highlights
The phase 3 trial results indicate that a single 3 g oral dose of zoliflodacin is non-inferior to the current standard of care (intramuscular ceftriaxone plus oral azithromycin) for treating uncomplicated urogenital gonorrhoea. With a microbiological cure rate of 90.9% compared to 96.2% for the comparator, zoliflodacin successfully met its primary endpoint within a 12% non-inferiority margin. Furthermore, the drug demonstrated a favorable safety profile, with primarily mild-to-moderate adverse events and no serious treatment-related complications reported. These findings position zoliflodacin as a potentially transformative oral treatment option in the global effort to combat multidrug-resistant Neisseria gonorrhoeae.
Background: The Escalating Challenge of Antimicrobial Resistance
Neisseria gonorrhoeae is a major global public health threat, consistently appearing on the World Health Organization’s list of priority pathogens due to its remarkable ability to develop resistance to every class of antibiotics used against it. For decades, the medical community has relied on ceftriaxone, often in combination with azithromycin, as the last remaining effective first-line treatment. However, reports of decreased susceptibility and outright resistance to ceftriaxone are increasing worldwide, raising the specter of untreatable gonorrhoea. The development of new antibiotic classes with novel mechanisms of action is therefore not merely a scientific pursuit but a global health necessity. Zoliflodacin, a first-in-class spiropyrimidinetrione, inhibits bacterial DNA gyrase and topoisomerase IV at a site distinct from fluoroquinolones, offering hope for a treatment that is not cross-resistant with existing therapies.
Study Design and Methodology
Trial Oversight and Participant Selection
This multinational, randomised, controlled, open-label, non-inferiority clinical trial was conducted across 17 outpatient clinics in Belgium, the Netherlands, South Africa, Thailand, and the USA. The study enrolled 1011 participants aged 12 years and older with clinical suspicion of uncomplicated urogenital gonorrhoea. Sites were selected based on high disease prevalence and the expertise of principal investigators in managing sexually transmitted infections (STIs) and HIV. Of the screened participants, 930 were ultimately randomised.
Intervention and Comparator Arms
Participants were randomly assigned in a 2:1 ratio to receive either a single oral dose of 3 g zoliflodacin or the standard comparator: 500 mg intramuscular ceftriaxone plus 1 g oral azithromycin. While the study was open-label for participants and clinicians, microbiology laboratory staff and the sponsor’s central study team remained masked until after the database lock to ensure the integrity of the microbiological results.
Primary and Secondary Endpoints
The primary efficacy endpoint was the proportion of patients achieving a microbiological cure at the test-of-cure (TOC) visit, which occurred 6 ± 2 days after treatment. Microbiological cure was defined as the eradication of Neisseria gonorrhoeae, as determined by urethral or endocervical culture. The non-inferiority margin was pre-specified at 12%, meaning the upper bound of the 95% confidence interval for the difference in cure rates (comparator minus zoliflodacin) had to be less than 12% to declare non-inferiority.
Key Findings: Efficacy and Non-Inferiority Results
Primary Efficacy Analysis
In the microbiological intention-to-treat (urogenital) population, zoliflodacin achieved a microbiological cure in 460 of 506 participants (90.9%, 95% CI 88.1–93.3). In the comparator group, 229 of 238 participants were cured (96.2%, 95% CI 92.9–98.3). The estimated difference between the two groups was 5.3%, with a 95% confidence interval of 1.4% to 8.6%. Because the upper bound of this interval (8.6%) was well below the pre-specified 12% margin, the study successfully demonstrated the non-inferiority of zoliflodacin. These results are particularly significant given the diversity of the study population, which included a high proportion of Black or African American (55%) and Asian (31%) participants.
Safety and Tolerability Profile
Zoliflodacin was generally well tolerated, with an adverse event profile comparable to the standard of care. The most common treatment-emergent adverse events in the zoliflodacin group were headache (10%), neutropenia (7%), and leukopenia (4%). In the comparator group, injection site pain was common (12%), followed by neutropenia (8%) and diarrhoea (7%). Importantly, the majority of these events were classified as mild or moderate in severity, and no serious adverse events were reported during the trial. The neutropenia observed was generally transient and not associated with clinical complications, though it warrants monitoring in future clinical use.
Clinical Implications and Expert Commentary
Biological Mechanism and Resistance Profiling
The success of zoliflodacin is rooted in its unique interaction with the DNA gyrase B subunit. Unlike fluoroquinolones, which target the A subunit, zoliflodacin’s binding site remains unaffected by the mutations that confer ciprofloxacin resistance. This makes it an ideal candidate for treating infections where existing resistance patterns limit therapeutic options. From a clinical perspective, the availability of a single-dose oral treatment is a major advantage. It eliminates the need for intramuscular injections, which can be a barrier to treatment adherence and patient comfort, and simplifies the logistics of STI clinic workflows.
Limitations and Generalizability
While the trial results are robust, certain limitations must be acknowledged. The study was open-label, which could theoretically introduce bias in reporting subjective adverse events, though the primary endpoint (microbiological culture) is an objective laboratory measure. Additionally, while the trial included 115 participants assigned female at birth, the majority of the population was assigned male at birth. Continued monitoring of efficacy in extragenital sites (pharyngeal and rectal) is also essential, as these sites often exhibit lower antibiotic penetration and higher rates of treatment failure compared to urogenital infections.
Conclusion: Advancing STI Management
The phase 3 trial of zoliflodacin marks a significant step forward in the management of uncomplicated urogenital gonorrhoea. By meeting the non-inferiority threshold against the current gold standard, zoliflodacin provides a much-needed oral alternative that could preserve the utility of ceftriaxone for more complex or disseminated infections. As public health agencies and clinicians face the mounting pressure of antimicrobial resistance, the introduction of a new antibiotic class with a novel mechanism of action offers a powerful tool to maintain control over one of the world’s most prevalent and resilient bacterial infections. Further implementation studies and real-world monitoring will be vital to integrate zoliflodacin into global treatment guidelines effectively.
Funding and Trial Registration
The trial was funded by a coalition of international partners, including the German Federal Ministry of Research, Technology and Space, the UK Department of Health and Social Care (via the Global Antimicrobial Resistance Innovation Fund), the Japan Ministry of Health, Labour and Welfare, and several Swiss and Dutch health departments. The trial is registered with ClinicalTrials.gov (NCT03959527) and EudraCT (2019-000990-22).
References
Luckey A, Balasegaram M, Barbee LA, et al. Zoliflodacin versus ceftriaxone plus azithromycin for treatment of uncomplicated urogenital gonorrhoea: an international, randomised, controlled, open-label, phase 3, non-inferiority clinical trial. Lancet. 2025 Dec 11:S0140-6736(25)01953-1. doi: 10.1016/S0140-6736(25)01953-1. Epub ahead of print. PMID: 41391465.
