A pragmatic trial with an optimized dose of rifampicin and moxifloxacin for the treatment of drug-susceptible pulmonary tuberculosis: a study protocol for open-label, randomized phase III trial (OptiRiMoxTB)

Abstract

Background

Current combination antibiotic treatment for drug-susceptible tuberculosis (DS-TB) usually takes 6 months to complete. This long duration can compromise clinical outcomes. Although a 4-month regimen including an optimized dose of rifapentine plus moxifloxacin is non-inferior to standard therapy, rifapentine is hard to source globally and adoption of this regimen has been slow. This trial investigates the efficacy and safety of a 4-month DS-TB treatment including the more readily available rifamycin, rifampicin 35 mg/kg, with or without moxifloxacin 400 mg.

Methods

This multi-centre phase III randomized open-label clinical trial will be conducted across four African countries (Gabon, Malawi, Mozambique and Tanzania). A total of 414 newly diagnosed consenting adult participants will be block randomized, after stratification by chest radiograph cavitation, to two experimental and one control arm at a ratio of 1:1:1. The first experimental group will receive optimized dose rifampicin (35 mg/kg) with routine weight-banded doses of isoniazid, pyrazinamide, and ethambutol once daily for 4 months. The second experimental group will receive optimized dose rifampicin (35 mg/kg) and moxifloxacin 400 mg once daily alongside routine doses of isoniazid and pyrazinamide. The control group will receive 6-month standard of care therapy: rifampicin (10 mg/kg) plus weight-banded dose of isoniazid, pyrazinamide, and ethambutol for 2 months, followed by the same doses of rifampicin and isoniazid for 4 months. Participants will be followed until the allocation of efficacy (TB-free survival) and safety (proportion of severe adverse events) outcomes. Secondary outcomes will also include the evaluation of the Tuberculosis Molecular Bacterial Load Assay (TB-MBLA) for microbiological treatment monitoring.

Discussion

This study will evaluate whether 4-month duration multi-drug treatment including an optimized dose of rifampicin with or without moxifloxacin has non-inferior efficacy and safety outcomes compared to standard of care DS-TB therapy in Africa.

Trial registration

ClinicalTrials.gov NCT05575518. Registered on 10th October 2022.

Introduction

Background and rationale {6a}

Tuberculosis (TB) is a major public health problem, particularly in low- and middle-income countries (LMICs). Timely administration and completion of effective treatment is crucial for TB control. Currently, most short course chemotherapy for drug susceptible (DS)-TB takes 26 weeks (6 months); an 8-week intensive phase of rifampicin (at a standard daily dose of 10 mg/kg), isoniazid, pyrazinamide, and ethambutol and a 16-week continuation phase of rifampicin and isoniazid. Treatment success is reported at 80% (95% confidence interval (CI): 78.4–81.7) overall, and 71% (95% CI: 63.7–77.8) for TB patients living with HIV [1]. This is below the World Health Organization (WHO) target of treatment success in 90% of cases [2].

Prolonged DS-TB therapy presents adherence challenges. Interventions such as Directly Observed Therapy (DoT) are difficult, expensive and only partially successful [3]. Medication side effects, including drug-induced liver injury (DILI), add complexity, which is further amplified for patients receiving anti-TB medicines alongside anti-retroviral therapy (ART) for human immunodeficiency virus (HIV) [4]. Interruption or premature discontinuation of TB treatment increases the risk of drug resistance and unfavourable outcomes. Mathematical models estimate that potent, shorter regimens will reduce TB incidence and deaths [5].

The international Phase 3 clinical trials, REMoxTB and RIFAQUIN, showed that 4-month experimental regimens containing the 8-methoxyfluoroquinolone, moxifloxacin and a standard-dose rifamycin (either rifampicin or rifapentine) achieved faster sputum sterilization than standard 6-month therapy for pulmonary TB, but improved clinical outcomes were thwarted by higher post-treatment relapse rates [6, 7]. Accumulative evidence from pre-clinical studies [8–10] and early-phase clinical trials have revealed improved bactericidal efficacy from rifampicin dose escalation [11], described the safety of rifampicin doses up to 40 mg/kg [12–14], and reported compatibility of rifampicin 35 mg/kg with dolutegravir-based ART [15]. Dose escalation studies of rifapentine (from 600 to 1200 mg daily) have provided similar results [16]. A Phase 2 Multi-Arm Multi-Stage (MAMS) study run by the Pan-African Consortium for the Evaluation of Anti-tuberculosis Antibiotics (PanACEA) suggested that a regimen containing both moxifloxacin and optimized dose rifampicin has treatment-shortening potential [14].

In 2021, the pivotal Phase 3 Study 31/A5349 trial confirmed that 4-month treatment containing optimized rifapentine 1200 mg plus moxifloxacin 400 mg is non-inferior to the standard 6-month TB approach [17]. Although this regimen has since been incorporated within WHO guidelines [18], global uptake has been slow, largely due to implementation challenges including limited worldwide availability of rifapentine [19]. Most national TB programmes still rely on rifampicin-based DS-TB treatment, so it is important to establish whether rifampicin can replace rifapentine in regimens of 4 months or shorter.

Primary and secondary microbiological endpoints in Phase 2 and 3 clinical trials of new anti-TB regimens are conventionally based on conversion from positive to negative, or the rate of bacillary clearance, from sputum culture. However, the laboratory methods used for mycobacterial culture are difficult to perform, generate results slowly, and provide data that correlate only modestly with long-term clinical outcomes [20]. The TB Molecular Bacterial Load Assay (TB-MBLA) is a molecular test based on specific Mycobacterium tuberculosis 16S ribosomal RNA (Mtb 16S-rRNA) quantification [21], which reads out much more quickly and is suitable for evaluation as a new microbiological tool to monitor treatment response and compare regimens.

Here we present OptiRiMoxTB, a Phase 3 clinical trial, conducted across four African countries to assess whether a 4-month treatment containing an optimized dose of rifampicin (35 mg/kg), with or without moxifloxacin (400 mg), is as effective and safe as standard 6-month therapy. A successful outcome will facilitate rapid implementation scale-up for public health impact. The secondary aims of the study include the evaluation of the TB-MBLA as a treatment response biomarker.

Objectives {7}

The OptiRiMoxTB trial aims to show whether one or both of two experimental regimens given for 16 weeks are non-inferior to standard treatment for DS-TB given for 26 weeks and could replace this under programmatic conditions.

Primary and secondary efficacy outcomes will be outlined in detail below. In brief, the primary efficacy objective will be evaluation of participant survival, free of tuberculosis 12 months after initiation of therapy. The primary safety objective will be to evaluate whether the experimental regimens are as safe and tolerable as standard treatment, based on assessment of the frequency of adverse events (AEs) of at least Common Terminology Criteria for Adverse Events (CTCAE) Grade 3 severity.

Secondary effectiveness objectives include assessment of longer-term TB-free survival out to 12 months after treatment completion, microbiological measurement of bacterial clearance (including TB-MBLA measurements) and clinical response incorporating participant-reported health status. Secondary safety objectives include more detailed AE comparisons between study arms, such as the proportion of treatment discontinuations or interruptions related to these.

Trial design {8}

This is a pragmatic phase 3 multi-centre, open-label, non-inferiority randomized controlled clinical trial with three parallel arms (two experimental regimens and control) and randomization by central allocation in a 1:1:1 ratio.

Methods: participants, interventions and outcomes

Study settings {9}

As shown in the “Administrative information” section, six clinical sites in four sub-Saharan African countries with moderate to high burdens of TB and HIV incidence [22, 23] will participate. All sites in Gabon, Malawi, Mozambique, and Tanzania are established clinical infectious disease research centres with appropriate facilities and capacity to recruit participants from rural and urban settings. These locations provide a good representation of populations across West, East, and Southern Africa Fig. 1.

Fig. 1.

OptiRiMoxTB: countries and trial sites. ¹ 2019 Global TB Report data used as these were the data at the time of initial study conception. Source of map: Africa Map Archives—GIS Geography; https://gisgeography.com

Eligibility criteria {10}

Participants must fulfil all the following inclusion criteria prior to enrolment:

1. Provide oral informed consent for study participation, including HIV testing if HIV status is unknown.

2. Have a diagnosis of pulmonary TB established by an Xpert MTB/RIF® result which confirms “low”, “medium” or “high” level detection of M. tuberculosis and does not detect rifampicin resistance.

3. Be aged ≥ 18 years (in Tanzania, Malawi and Mozambique) and ≥ 21 years (in Gabon) on the day of providing informed consent.

4. Have a body weight in light clothing and without shoes of ≥ 35 kg

5. Have a negative urine or serum pregnancy test ≤ 7 days prior to screening, and consent to practice an effective method of contraception until completion of therapy (Female participants of child-bearing potential only).

6. Have a verifiable residence location and telephone number for contact during follow-up.

Individuals for whom one of the following criteria is met will be excluded from the trial:

1. Any circumstances raise concern about the provision of free, informed consent to the study.

2. Sputum Xpert MTB/RIF® assay result is “negative”, “trace” or “very low” positive.

3. Any pre-treatment M. tuberculosis isolate, either cultured or detected through molecular assays from sputum, is resistant to one or more of rifampicin, isoniazid, pyrazinamide, ethambutol, or fluoroquinolones.

4. Poor general condition where delay in treatment cannot be tolerated, or death within 3 months is likely, as assessed by the investigator.

5. A nose/throat swab is positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), on polymerase chain reaction (PCR) or a rapid diagnostic test within 14 days of enrolment.

6. Pregnancy or breast-feeding (female participants only).

7. Unable to take oral medications.

8. Received any investigational drug in the past 3 months.

9. Received more than 5 days of treatment directed against active tuberculosis within 6 months of enrolment.

10. Known intolerance or contraindications to any of the study drugs.

11. Unwilling or unable to adhere to requirements regarding restricted use of other medications during the study. Restricted medications will include medications which prolong the QTc interval, and CYP450 inhibitors or inducers.

12. Due to initiate, or requires continuation of, non-efavirenz, non-dolutegravir-based anti-retroviral therapy for HIV infection.

13. Decompensated liver disease and/or aminotransaminases > 3 × upper limit of normal (ULN), serum total bilirubin level > 1.5 × ULN or serum/plasma creatinine level > × 2 ULN.

14. A baseline QTc interval of > 450 ms on electrocardiograph (ECG).

15. Being, or about to be, treated for malaria.

16. Co-existent medical conditions that, in the investigator’s judgement, make study participation not in the individual’s best interest.

Who will take informed consent? {26a}

Information about the trial will be provided by study doctors and nurses who have completed Good Clinical Practice in Research (GCP) and study protocol training. Participants will be invited for screening if they are suspected to have pulmonary TB based on sputum smear microscopy or GeneXpert MTB/RIF done within the government or private health sector. Screening may continue for a maximum of 5 days. After providing valid informed consent, participants will be screened using all inclusion and exclusion criteria. The study database will contain a record of every screening, irrespective of outcome. Individuals who are successfully recruited will be randomized. Those who are ineligible will be referred for routine TB or other appropriate medical care.

Additional consent provisions for collection and use of participant data and biological specimens {26b}

Additional consent form will be provided to participant requesting to use their leftover sputum and blood samples stored in the lab for future studies to advance TB research.

Interventions

Explanation for the choice of comparators {6b}

The choice of rifampicin dose (35 mg/kg) in both experimental arms is based on prior studies designed to optimize efficacy and safety of this drug, particularly in African populations. However, some recent meta-analyses have also reported increased rifampicin tolerability concerns at doses above 20–30 mg/kg [24, 25], so particular care will be given to analysis of tolerability and toxicity data in this study.

Both the PanACEA-MAMS trial [14] and Study 31/A5349 [17] indicated that combining optimized dose rifamycins with moxifloxacin is likely to confer additional benefit, perhaps because of high fluoroquinolone penetration into pathological TB lesions [26]. Therefore, one experimental arm contains both optimized dose rifampicin and moxifloxacin.

The 6-month control comparator of rifampicin (10 mg/kg)-isoniazid-pyrazinamide-ethambutol was chosen as it remains the most commonly used DS-TB regimen worldwide.

Intervention description {11a}

Details of each treatment arm are shown in Fig. 2. Study medications will be administered as a mixture of fixed dose combination (FDC) and single drug formulation tablets.

Fig. 2.

OptiRiMoxTB study schematic and drug dosing

In experimental Arm 1, participants will receive an optimized dose of rifampicin (35 mg/kg/day) plus a standard weight-banded dose of isoniazid, pyrazinamide and ethambutol administered orally once a day for a duration of 4 months (4R₃₅HZE). Arm 2 is similar to Arm 1 except ethambutol is replaced by moxifloxacin 400 mg (4R₃₅HZM). The 6-month control arm regimen consists of a standard dose of rifampicin (10 mg/kg/day) plus isoniazid with or without pyrazinamide and ethambutol administered orally once a day for 2 months of rifampicin followed by 4 months of rifampicin 10 mg/kg with a weight-banded dose of isoniazid (4R₁₀H).

Participants in Arms 1 and 2 will be advised to take their medications early in the morning with a light meal to reduce the risk of gastrointestinal irritation with optimized dose rifampicin. Those in the control arm will be advised to take their medications with a glass of water first thing in the morning on an empty stomach (1 h before or 2 h after food) for best rifampicin absorption. If medication upsets the stomach when taken fasted, it may be taken with a small amount of food.

Manufacturers of trial medications are as follows: Lupin Limited, India (for FDC RHZE and RH tablets); Macleods Pharm Ltd, India (for rifampicin 150 mg and 300 mg capsules); Oxalis Lab, India (for pyrazinamide 400 mg tablets); and MSN Laboratories Pvt Ltd, India (for Moxifloxacin 400 mg tablets). All manufacturers are certified and adhere to good manufacturing practice. IMP supply will be handled by the Global Drug Facility, in accordance with manufacturers’ specifications.

Criteria for discontinuing or modifying allocated interventions {11b}

Participants may be withdrawn from the trial during treatment or follow-up because of withdrawal of informed consent, late exclusion (identification of information confirming that one or more exclusion criteria are met after full enrolment), safety concerns by site investigators (including adverse events or concern about worsening TB and/or bacteriological failure/relapse that requires a change in TB treatment), pregnancy, at the request of the sponsor, or loss to follow-up.

Participants withdrawn from the trial will not routinely be replaced.

Strategies to improve adherence to interventions {11c}

At site pharmacies, study medications will be repacked into daily doses and dispensed by trial pharmacists or trained dispensers who are also responsible for documentation in source data and on dispensing and adherence eCRFs. Trial medications will be provided to participants during follow-up visits on day 14, 28, 56, 84, 112 and 168. Adherence to interventions will be assessed using pill counts during each clinic visit and automatically calculated in the adherence eCRF. Adherence to trial medications will be reinforced by routine counselling, with study staff observing uptake of one dose during each visit while the rest of the doses will be taken at home under the support of an identified relative or friend treatment supervisor.

Relevant concomitant care permitted or prohibited during the trial {11d}

Absorption of moxifloxacin is reduced by multivalent cation-containing medications, e.g. aluminium and magnesium-containing antacids. Proton pump inhibitors, e.g. omeprazole, are preferred antacids.

TB patients living with HIV are eligible if they are already taking or newly initiating ART regimens composed of two nucleosides (or nucleotide) reverse transcriptase inhibitors (other than stavudine and didanosine) plus efavirenz/dolutegravir. Those taking dolutegravir will be required to increase the dose to 50 mg twice daily for the duration of TB treatment.

New TB patients who are being, or are about to be, treated for malaria will be excluded from enrolment. Should a participant develop malaria during the trial, anti-malarial treatment may be offered in accordance with national malaria treatment guidelines, but careful consideration must be given to electrocardiographic QTc-prolonging potential and drug-drug interactions involving available anti-malarial drugs.

Individuals who have received QTc prolonging medications within 30 days of the first dose of study drugs will be excluded, to avoid the risk of QTc exacerbation with moxifloxacin [27]. Exceptions may be made for those who have received 3 daily doses or less, and at least 5 elimination half‐lives of the drug have passed before the first dose of study treatment. The list of medications with the risk of QTc prolongation is accessible at https://crediblemeds.org.

Provisions for post-trial care {30}

Participants who leave the study due to adverse events or unfavourable TB treatment outcomes will be referred locally for appropriate medical care or ongoing TB management via National TB Programmes.

Outcomes {12}

The primary efficacy endpoint for this trial is participant survival, free of tuberculosis 12 months after randomization. For this favourable outcome to be allocated, all the following criteria will require to be met:

1. Completed assigned treatment and known to be alive

2. Stable sputum culture conversion, or clinically well without features of ongoing active TB and unable to provide a sputum culture result, either because sputum can no longer be produced or because the only available sample is contaminated without evidence of Mtb

3. Have not met criteria for treatment failure or relapse

4. Not in need of TB treatment and having required no substantial treatment modifications or additional treatment for TB outside the study regimen.

Unfavourable primary efficacy outcomes will be allocated to participants who exit the study under any of the following circumstances:

1. Completed assigned treatment in the absence of bacteriological cure. This typically occurs as a consequence of treatment failure (defined as submitting two sputum samples with positive culture for Mtb on different visits, when the first of these samples was collected at or after 2 weeks prior to the scheduled end of treatment) or TB relapse (defined as submitting two sputum samples with positive culture for Mtb on different visits, when the first of these samples was collected after completion of scheduled TB therapy and where at least one of the Mtb isolates is genetically similar to the baseline strain).

2. Completed assigned treatment with a single positive culture for Mtb when last seen, but not confirmed by a second sample, unless the positive culture is deemed to represent re-infection.

3. Death from any cause during study treatment, except violent or accidental death (e.g. road traffic accident).

4. Extension or alteration of TB treatment beyond that permitted by the protocol.

Circumstances during the study which may result in unassessable outcomes include:

1. Failure to complete treatment

2. Completion of assigned treatment, then loss to follow-up, with the last reported culture being negative for Mtb

3. Women becoming pregnant during TB therapy and withdrawing from the trial

4. Death from a violent or accidental cause

5. Detection of TB re-infection, after successful completion of their assigned therapy, with a new strain of Mtb, demonstrated to be genetically different from that identified at study entry.

The following secondary efficacy endpoints will be reported.

• Participant survival, free of tuberculosis at 12 months after treatment completion following extended follow-up arranged beyond the formal project end.

• Microbiological response using BD Mycobacteria Growth Indicator Tube 960®liquid culture time to positivity (MGIT-TTP)

• Microbiological response using the TB-MBLA (including time to conversion to negative and rate of decline in estimated colony-forming units/ml of sputum).

• Clinical response to therapy, including change from baseline clinical measurement of weight, body mass index (BMI), TB symptoms and patient-reported health status.

The primary safety outcome for this trial will be the occurrence of AEs of CTCAE Grade 3 severity or higher.

The following secondary safety outcomes will also be reported:

• Occurrence of AEs of any grade reported and regarded as definitely, probably or possibly related to study drugs

• Treatment discontinuations or interruptions related to AEs

• Frequency, severity and type of AEs

During each visit at day 14, 28, 56, 84, 112, 182, months 9 and 12, participants will undergo assessments including self-reported health status, physical examination, routine clinical laboratory tests, particularly serum creatinine, total bilirubin, alanine transaminase (ALT) and blood count (Hb, WBC and platelet count).

Participant timeline {13}

Participants will be followed according to the schedule of events elaborated in Fig. 3.

Fig. 3.

Schedule of enrolment, intervention and assessment

Sample size {14}

Sample size has been calculated based on the primary efficacy outcome of participant survival free of TB 12 months after initiation of treatment. Based on previous trials of new DST-TB therapy in similar populations (the REMoxTB [6] and STAND [28] studies) in similar populations, it has been estimated that 6% and 10% of participants will have unfavourable primary and non-assessable primary efficacy outcomes, respectively. For OptiRiMoxTB, with power (β) set at 90%, a non-inferiority margin of 10%, and a type I error (α) of 5%, a total of 414 participants (138 participants per arm in a 1:1:1) across all sites will be required to show non-inferiority of either of the experimental regimens to control.

Recruitment {15}

All sites will recruit via networks of satellite centres, particularly primary and secondary health facilities. This will be achieved through meetings with healthcare providers at potential health centres and use public liaison activities designed during our prior experience of clinical trial conduct at the same sites.

Available information on rates of new TB diagnoses at clinics affiliated with each study site, informed pre-trial projections of likely participant numbers in each study country to be set as follows: Gabon, 50; Malawi, 104; Mozambique, 100; and Tanzania, 160.

Assignment of interventions: allocation

Sequence generation {16a}

Randomisation of eligible participants will be stratified according to the presence or absence of cavitation on chest radiograph. Stratified randomization will be undertaken within Research Electronic Data Capture (REDCap) software [29] on a 1:1:1 allocation ratio using a permuted block randomization procedure with block sizes of 3, 6 and 9.

Concealment mechanism {16b}

Allocation concealment to reduce selection bias at randomization is fostered by REDCap, which provides a randomization number only after all screening information has been provided on the CRF. Following randomization, the study will be open label, with treatment allocation known to participants and healthcare providers.

Implementation {16c}

The allocation sequence generation will be released automatically by REDCap software upon confirmation of participant eligibility on the eCRF.

Assignment of interventions: blinding

Who will be blinded {17a}

Not Applicable. Not applicable because this is an open-label trial, so site investigators and participants will be aware of treatment allocations.

Procedure for unblinding if needed {17b}

Not applicable. Not applicable because this is an open-label trial, so site investigators and participants will be aware of treatment allocations.

Data collection and management

Plans for assessment and collection of outcomes {18a}

Study endpoints are based on a combination of objective clinical observations and microbiological measurements. An outcome allocation committee, comprising the Principal Investigators, study statistician, and independent medical experts appointed by the Sponsor will meet at study completion to confirm assignment of final outcomes for each participant.

Plans to promote participant retention and complete follow-up {18b}

Careful participant counselling and community engagement will reinforce the importance of study visit attendance from the point of screening onwards. Participants will have clear contact details for local site investigators to report any concerns as soon as they arise. If visits are missed, at least three attempts at contact via telephone or home visits will be undertaken before any participant is allocated as lost to follow-up.

In general, participants who withdraw from the study for reasons other than withdrawal of consent or loss to follow-up shall continue to follow study assessments as laid down in the schedule of events to make them evaluable for long-term outcomes.

Data management {19}

All study data will be entered into eCRF forms, created for each participant in REDCap. Physical source data, including participant’s case records, chest radiographs, and safety and microbiology laboratory results, will be retained and made available for verification. Accuracy and completeness of data will be checked by pre-programmed edit checks in the REDCap database that will flag out-of-range values and by at least two visits to each site by independent monitors.

Site lead investigators are responsible for ensuring that study documents are maintained in accordance with International Conference on Harmonisation of Good Clinical Practice (ICH-GCP) guidelines. Upon trial completion, essential documents will be retained for a duration of not less than 10 years or as required by local regulation.

Confidentiality {27}

In the trial database and on all study forms, participants will only be identified by a study number comprising three letters which represent the site and three numbers which represent their enrolment number. A participant identification log will be kept in a securely locked separate trial file at each site, to which only delegated staff will have access. The ICF has a clause granting permission for the review of participants’ source documents by site lead investigators or a competent delegated person if necessary. The trial database will be encrypted and stored on secure servers with regular back-up and access control.

Plans for collection, laboratory evaluation and storage of biological specimens for genetic or molecular analysis in this trial/future use {33}

Sputum samples at screening and enrolment will be used to confirm the diagnosis of pulmonary tuberculosis by sputum smear microscopy and/or Xpert MTB/RIF, and to perform rapid drug susceptibility testing for rifampicin. Sputum from all timepoints will be used for mycobacterial liquid (MGIT) culture and the molecular bacterial load assay (TB-MBLA). M. tuberculosis isolates from these cultures will be stored and may be used for additional drug susceptibility testing. Isolates from participants who remain sputum culture positive at the end of treatment or develop recurrent TB after treatment completion will be stored for Whole Genome Sequencing to confirm whether it is a relapse or reinfection.

Statistical methods

Statistical methods for primary and secondary outcomes {20a}

Study analysis groups will be defined and analysed as shown in Table 1. The primary efficacy outcome will be assessed by comparing each of the experimental regimens with the control arm in the modified intention-to-treat (mITT) population. In each comparison, non-inferiority will be assessed by comparing the upper bound of a 95% two-sided confidence interval for the difference between the proportion of participants who were classified with an unfavourable outcome on the control and experimental regimen to the pre-defined non-inferiority margin of 10%.

Table 1.

OptiRiMoxTB study analysis populations

Analysis population	Definition
Intention-to-treat (ITT)	All enrolled participants who receive a treatment assignment Participants with an unassessable primary efficacy outcome will be assumed to have had an unfavourable outcome
Modified intention-to-treat (mITT)	All ITT participants except late exclusions This is the primary analysis population for efficacy analyses Participants with an unassessable primary efficacy outcome will be assumed to have had an unfavourable outcome
Per-protocol (PP)	All participants who completed the study without protocol deviations and had an outcome assigned Participants with an unassessable outcome will be excluded from the analysis
Safety	All ITT participants that receive at least one dose of study medication This is the primary analysis population of interest for safety analyses

The primary safety outcome will be assessed by comparing the proportion of participants with CTCAE grade 3 or higher AEs in each experimental regimen versus the control regimen, in the pre-defined safety population.

In secondary efficacy analyses, the primary efficacy endpoint will be assessed in the PP population, and the secondary efficacy endpoints will be assessed in both mITT and PP populations. Both experimental regimens will be compared with the control regimen. Secondary analyses will include those directed towards the identification of clinical and microbiological factors associated with favourable and unfavourable outcomes. Mixed effects models will be used to analyse microbiological culture and TB-MBLA data on bacillary clearance rates. Time to unfavourable outcome and time to microbiology-negative status will be analysed using Kaplan-Meier plots and Cox proportional hazards regression methods. Multivariate logistics regression modelling will be used to assess relationships between co-variates and clinical outcomes.

As with the primary safety outcome, all secondary safety outcomes will be assessed in the pre-defined safety population.

Interim analyses {21b}

Not Applicable. Not applicable because there will be no interim analysis apart from Data and Safety Monitoring Committee (DSMC) reports which will be generated following the review of unblinded data in closed meetings.

Methods for additional analyses (e.g. subgroup analyses) {20b}

Sub-group analyses (with tests for interaction) of the primary endpoint will be performed according to age, gender, weight, BMI, country, HIV status, smoking history and history of diabetes, the presence or absence of cavitation (cavitation will be defined as a gas-containing lucent space at least 1 cm in diameter within the lung parenchyma surrounded by an infiltrate or fibrotic wall greater than 1 mm thick seen on the chest radiograph), extent of cavitation on baseline chest radiograph, MGIT days to detection, initial bacterial load in sputum as indicated by baseline MIGT-TTP result (low bacterial load = MIGT-TTP ≥ median, high bacterial load = MIGT-TTP < median) and GeneXpert MTB/RIF Cycle threshold. The test for an interaction between the covariate and treatment will be done using logistic regression comparing the model including the interaction term and the model with only marginal terms using the likelihood ratio test to evaluate the statistical significance of the inclusion of the interaction term in the model.

Methods in analysis to handle protocol non‑adherence and any statistical methods to handle missing data {20c}

Although the primary study analysis will be the mITT population, sensitivity analyses will be undertaken to consider the effect of missing data on study outcomes. These will include primary efficacy analyses on ITT and PP populations.

To minimise missing information, following data entry into eCRFs, completeness and consistency checks will be performed by sponsor’s data management. All resulting queries will be sent through the database query system to leave an audit trail.

Plans to give access to the full protocol, patient level‑data and statistical code {31c}

With exception of participant-identifying information which will not be shared, all other data from this trial will be released through public use data set.

Oversight and monitoring

Composition of the coordinating centre and trial steering committee {5d}

A trial Operational Team (OT) chaired by the Trial Project Manager, comprising two co-Principal Investigators, a Sponsor Trial Manager, and all site Lead Investigators, alongside data, microbiology/biomarker and pharmacy project leads, will meet every 2 weeks to co-ordinate day-to-day operations. Additionally, a Trial Steering Committee (TSC), comprising a sponsor representative, the trial statistician, and two expert clinicians who are independent of trial conduct, will convene on an ad hoc basis throughout the trial, reporting to the sponsor.

A Medical Monitoring Team (MMT) comprising two co-Principal Investigators and two independent clinicians from experienced African TB trial sites which are not involved in OptiRiMoxTB will provide real-time oversight (with response time to queries of 24 h) of clinical activities at all sites: primarily offering guidance on management and reporting of safety events, including decisions on participant withdrawal from the study. The MMT will report directly to the Sponsor and may present at OT or TSC meetings as required. On request, the MMT may compile information or provide reports to the Data Safety Monitoring Committee (DSMC).

Composition of data safety monitoring committee, its role and reporting structure {21a}

The DSMC will consist of five members: two trial statisticians (one of whom has extensive experience of TB trials, and will be chair), and three clinicians (one Infectious Disease physician, one Respiratory Medicine physician and one Clinical Pharmacologist). The DSMC will be balanced by gender and geography (with African and European members who are experienced not only in clinical TB research but also in the specific study settings and context). DSMC members will be independent of the sponsor and study investigators and have no competing interests. They will meet on a prespecified schedule: before initiation of recruitment, after month 6, and then when one-third, two-thirds and all participants have been enrolled. Additional ad hoc meetings will be convened if required by the sponsor. The DSMC acts in an advisory capacity to the Sponsor through TSC to safeguard the integrity of trial conduct and participant safety. After each assessment, the DSMC will make recommendations to the Sponsor about continuation, modification, or termination of the entire study or of individual arms.

Adverse event reporting and harms {22}

All participants will be counselled during informed consent to report any AEs experienced at any time during the study. Additionally, information on AEs will be proactively sought during each study visit by direct clinical assessment (interview and physical examination and laboratory investigations as outlined in Fig. 2). Severity of AEs will be classified on a scale of 1–5 according to the United States (U.S.) National Institutes of Health CTCAE 5.0 [30]. Site lead investigators will categorize causal relationships of AEs to study drugs as ‘unrelated’, ‘unlikely’, ‘possible’, ‘probable’ and ‘certain’. The MMT will be used as a resource to assess and manage AEs. All AEs will be recorded. Those with a severity grading of 3–5 will be defined as severe adverse events (SAEs), which carry an obligation to report to the Sponsor, regulatory authorities and independent ethical committees within 24 h of first identification.

All women of child-bearing age will be counselled to contact their site investigator immediately if they suspect that they might be pregnant at any time. If pregnancy is confirmed, the participant will be withdrawn from the trial and referred to their National TB Program for ongoing care. Investigators will also report to the Sponsor follow-up information regarding the outcome of the pregnancy, including perinatal and neonatal outcomes.

Adverse events involving hepatotoxicity are of particular interest in this trial, and specific Hepatotoxicity Management Guidelines will be used. Participants with aminotransaminases ≥ 3 × ULN or bilirubin ≥ 2 × ULN will be instructed to withhold all trial medications, with further guidance based on repeat blood tests, clinical condition, and MMT consultation.

Frequency and plans for auditing trial conduct {23}

Qualified independent trial monitors, appointed prior to trial initiation by the Sponsor, will visit each site at least twice during the trial to audit performance.

Plans for communicating important protocol amendments to relevant parties (e.g. trial participants, ethical committees) {25}

All changes to the protocol will be completed by means of amendments, which will be submitted to applicable ethical committees and regulatory agencies prior to implementation. Amendments of trial protocol will be updated in ClinicalTrials.gov ID: NCT05575518. Protocol amendment training will be performed as necessary.

Dissemination of results {31a}

The findings from this trial will be important to study participants, communities affected by TB, and to clinicians, public health policymakers, and researchers working on TB treatment and control. Results will be disseminated to each group by appropriate means including aggregate data reports to study participants and community advisory boards, scientific conference presentations, and submission of manuscripts for publication in open access peer-reviewed journals.

Discussion

The OptiRiMoxTB trial builds on previous work, including some of the same group that described the tolerability of rifampicin doses up to 35 mg/kg in African populations by offering Phase 3 evaluation of DS-TB treatment regimens using that dose. It also builds on the important work of the TBTC Study 31/ATCG5349 trial, which indicated that optimized dose rifamycins may need to be accompanied by lesion-penetrating 8-methoxyfluoroquinolones to achieve the goal of treatment-shortening [6]. Since initiation of this protocol, the RIFASHORT trial has published results indicating that flat dosing of 1200 mg and 1800 mg rifampicin (equivalent to 20 mg/kg and 30 mg/kg, respectively, in a 60 kg adult) combined with other first-line TB drugs did not achieve non-inferiority compared to standard of care therapy [30]. OptiRiMoxTB advances on that work by weight-based rifampicin dose escalation and incorporation of an experimental arm containing moxifloxacin.

In order to generate data which is generalizable to programmatic delivery of routine TB care in high-burden countries and which may accelerate implementation of successful study regimens, the trial will be conducted in African study sites with moderate-to-high HIV prevalence and the study design has been kept as pragmatic as possible: eligibility criteria have been kept as broad as possible, there are no specific HIV severity or CD4-count threshold-based exclusion criteria, and procedures at study visits have been rationalized to those which are deemed essential. Since protocol initiation, systematic reviews have ongoing uncertainty on the optimal tolerable dose of rifampicin [24, 25], underpinning the need for the careful safety monitoring, which will be provided by site investigators, the MMT, and the independent DSMC.

The primary efficacy endpoint of this trial is clinical, but secondary microbiological endpoints will include measurements using conventional MGIT-TTP and also the novel TB-MBLA assay. Comparative performance of these assays will be important for the design and conduct of future Phase 2 and 3 clinical trials and may also provide insights on the value of TB-MBLA for treatment monitoring in routine TB care.

The open-label design of this trial is driven by the complexity and pill burden, which would be generated by placebo-controls, but does pose a risk of reporting bias at the point of outcome allocation. This will be mitigated by use of standard prospective outcome definitions, incorporating objective laboratory evidence of stable culture conversion, and appointment of an outcome allocation committee containing independent medical experts.

Primary endpoints for this trial will be measured 12 months after participant randomization, partly because this timepoint was deemed practically achievable during the prescribed funding window at the time of study design. Acknowledging that post-treatment relapse is an important component of long-term outcome in Phase 3 TB trials, secondary outcomes do include scope for longer-term outcomes (until at least 12 months after treatment completion). Sufficient resources are now in place for extended follow-up, and a further protocol amendment (v3.0) is in process to approve data collection for this.

Ultimately, this pragmatic Phase 3 trial will establish whether 4-month DS-TB treatment incorporating optimized dose rifampicin (35 mg/kg) with or without moxifloxacin (400 mg) is efficacious and safe compared to 6-month standard treatment with rifampicin (10 mg/kg). The study design, based on routine care delivery to a representative patient population, and use of a readily available rifamycin may pave the way for accelerated programmatic implementation.

Trial status

OptiRiMoxTB was registered at ClinicalTrials.gov, ID: NCT05575518 with trial version 1.0 on 10th October 2022. Four clinical sites were included at that time (CERMEL, Gabon; KUHeS, Malawi; INS, Mozambique; KIDH, Tanzania). At KIDH, recruitment started on August 2023. The protocol was amended to version 2.0 on 30th November 2023, primarily to allow site expansion to include IHI and NIMR-Mwanza in Tanzania. These sites started recruitment in 2024. The protocol was further amended to version 3.0 on 8th January 2025 to increase follow-up time from 12 to 18 months post-randomization. Recruitment of the first participant was on 11th August 2023, and the last participant was recruited on 6th January 2025. Currently, participants are being followed up, expecting the last participant's last visit to be on 25th May 2026.

Abbreviations

16S

16Svedberg unit

2R₁₀HZE

Two months duration of standard daily rifampicin (R) 10 mg/kg plus standard weight banded dose of isoniazid (I), pyrazinamide (Z) and ethambutol (E)

4R₁₀H

Four months duration of standard daily rifampicin (R) 10 mg/kg plus standard weight banded dose of Isoniazid (I)

4R₃₅HZE

Four months duration of daily rifampicin (R) 35 mg/kg plus standard weight banded dose of isoniazid (I), pyrazinamide (Z) and ethambutol (E)

4R₃₅HZM

Four months duration of daily rifampicin (R) 35 mg/kg plus standard weight banded dose of isoniazid (I), pyrazinamide (Z) and moxifloxacin(M)

AEs

Adverse events

ALT

Alanine transaminase

ART

Anti-retroviral therapy

BD MGIT 960®

Becton, Dickinson Mycobacteria Growth Indicator Tube 960®

BD MGIT-TTP 960®

Becton, Dickinson Mycobacteria Growth Indicator Tube 960® liquid culture time to positivity

BMI

Body mass index

CD4

Cluster of differentiation 4

CERMEL

Centre de Recherches Médicales de Lambaréné

CH-GCP

International Conference on Harmonization of Good Clinical Practice

CISPOC

Polana Caniço Health Research and Training Center

COVID-19

Coronavirus disease-19

CRF

Case report form

CTCAE

Common Terminology Criteria for Adverse Events

CYP450

Cytochrome P450

DILI

Drug-induced liver injury

DoT

Directly observed therapy

DSMC

Data and Safety Monitoring Committee

DS-TB

Drug-susceptible tuberculosis

ECG

Electrocardiograph

eCRF

Electronic-case report form

EDCTP2

Europe and Developing Countries Clinical Trials-2

EN

Enrolment

FDC

Fixed dose combination

FDC RH

Fixed combination of rifampicin (R) 150 mg and isoniazid (H) 75 mg

FDC RHZE

Fixed dose combination of rifampicin (R) 150 mg, isoniazid (H) 75 mg, pyrazinamide (Z) 400 mg and ethambutol (E) 275 mg

GCP

Good Clinical Practice in Research

Hb

Hemoglobin

HIV

Human immunodeficiency virus

ICF

Informed consent form

IHI

Ifakara Health Institute

INS

Instituto Nacional de Saúde

ITT

Intention-to-treat

KIDH

Kibong’oto Infectious Diseases Hospital

KUHeS

Kamuzu University of Health Sciences

LMICs

Low- and middle-income countries

M. tuberculosis

Mycobacterium tuberculosis

M2, M4, M6

Month two, month four, month six

MAMS

Multi-arm multi-stage

MDR/RR TB

Multi-drug resistant/rifampicin-resistant tuberculosis

mITT

Modified intention-to-treat

MMT

Medical Monitoring Team

Mtb

Mycobacterium tuberculosis

NIMR

National Institute for Medical Research

OT

Operational Team

PanACEA

Pan-African Consortium for the Evaluation of Anti-tuberculosis Antibiotics

PCR

Polymerase chain reaction

PP

Per-protocol

REDCap

Research Electronic Data Capture

RNA

Ribonucleic acid

rRNA

Ribosomal ribonucleic acid

SAEs

Severe adverse events

SARS-CoV2

Severe acute respiratory syndrome coronavirus 2

SCR

Screening

SPIRIT

Standard Protocol Items: Recommendations for Interventional Trials

TB

Tuberculosis

TB-MBLA

Tuberculosis Molecular Bacterial Load Assay

TSC

Trial Steering Committee

ULN

Upper limit of normal

US

United States

WBC

White blood count

WHO

World Health Organization

Authors’ contributions {31b}

The trial was conceptualized by DJS, SM and SHG. The study design was conceived by DJS and SM. SHG, who also wrote the protocol, and HM, DJS, SGM, and SHG wrote this manuscript. Study set-up and conduct is being undertaken by HM, AL, EM, OLK, SL, HS, TDMcH, LW, WS, BRA, ML, CK, PM, BM, KJ and SGM. All authors read and approved the final manuscript.

Funding {4}

The trial is funded by the Europe and Developing Countries Clinical Trials-2 (EDCTP2) Simplified short treatment for tuberculosis grant RIA2017S-2012. The funder had no role in the design of the study and writing this manuscript. Also, the funder will have no role in data collection, analysis, interpretation and reporting the trial findings.

Data availability {29}

All parties conducting the trial will have access to the final dataset.

Declarations

Ethics approval and consent to participate {24}

Ethical approvals for this trial have been sought from all sites’ local and/or national ethical committees; Tanzania (KIDH and National Institute of Medical Research (NIMR)), Gabon (CERMEL and National Research Ethics Committee), Malawi (KUHeS Ethical Committee), and Mozambique (INS Institutional Review Board and Comité Nacional de Bioética para Saúde). Also, the trial has received clinical trial authorization from medicines regulatory authorities in all participating countries, namely; Tanzania Medicines and Medical Devices Authority (TMDA), Malawi Pharmacy and Medicines Regulatory Authority (PMRA), Gabon Directorate of Medicines and Pharmacy (DMP) and Mozambique Autoridade Nacional Regulatoria de Medicamentos (ANARME).

Consent for publication {32}

Written informed consent will be obtained from all participants prior to enrolment. Original ICFs will be kept in regulatory binders at each site and will be available on request.

Competing interests {28}

None of the authors has any competing interest to declare. In addition, the funder has no influence on design, implementation and reporting of this clinical trial research.