Due to heavy traffic generated by the COVID-19 pandemic during early 2020 and limited ability to use the on-line search portal for the WHO ICTR, we downloaded the full ICTR database (3.5GB, 19 May 2020) and used it for this systematic analysis. From 632,787 clinical trials registered, we identified 2205 with condition containing ‘tb’ or ‘tubercul’ and selected 510 for independent registry review by two reviewers. All registry information was available in English. From these, we identified 51 trials that were highly likely to be relevant and eligible for inclusion (See Figure 1 for PRISMA flow diagram(14)). We then contacted Principal Investigators of the selected trials to request the most current versions of their protocols and, when possible, SAPs. We received protocols from 31 studies, and SAPs from 18 (58%). Many trials were listed on more than one trial registry; the majority (27, 87%) were listed at least on clinicaltrials.gov; two of the studies was only listed on ISRCTN registry (isrctn.com), and two trials were only listed on Clinical Trials Registry of India (ctri.nic.in). Registration across all trials was finalized between the years of 2001 and 2020 (although in some early cases, trials were not registered until after completion; the earliest trial began enrolling in 1995 but was not registered until 2001), with 21 (68%) of the trials registered during or after 2010. All protocols were available in English. Twenty-six of the trials (84%) were phase III, either with (n=29) or without (n=2) internal controls; one trial was described as phase IIB/III, two were listed as phase IIC, and two as phase IV (see Table 1).
Ten of the trials targeted patients with drug-resistant TB (DR-TB) and the remaining 21 trials enrolled patients whose TB was drug susceptible (DS-TB). Two protocols included patients diagnosed with either DS- or DR-TB, although in each case those with DR-TB were enrolled as a non-randomized interventional cohort that was not ”statistically analyzed.” Five (17%) of the trials included participants enrolled in African sites, eight (26%) included participants enrolled in Asian sites, and 16 (52%) included participants enrolled on both continents. Seven (24%) included subjects in South American sites, two (7%) in Latin America and five (17%) in North America. Proposed subjects were as young as 12 (one trial), 14 (two trials) and 15 (four trials), although one trial did not impose a lower age limit; however, most trials included patients aged 18 years and older. Two protocols capped the age of participants at 60, five at 65, one at 70, and another at age 75; in the remaining trials, an upper age limit was not specified. Only one trial exclusively conducted in children and adolescents was included in the 51 trials for protocol and SAP review, but the protocol was not made available for inclusion in our review.
The primary objective uniformly across all but one study was to investigate whether a novel treatment regimen had non-inferior or superior efficacy in terms of a “long-term durable cure extending through post-treatment follow-up.” In the remaining study, efficacy outcomes were secondary to safety outcomes. Novel interventions varied across trials, and included shortening treatment, evaluating the efficacy of new combination regimens, utilizing oral medications exclusively, testing different doses and durations of treatment, testing fixed dose combination formulations, and simplifying treatment by utilizing intermittent dosing. A non-inferiority analysis comparing a new treatment regimen to standard treatment was specified in 18 (58%) protocols, with margins of non-inferiority ranging from 4% to 12%. Other techniques used included equivalence testing (n=6), superiority testing (n=3) and logistic regression to compare differences in proportions of participants achieving a Favorable outcome (or, conversely, an Unfavorable outcome). In 15 (48%) protocols, an intention-to-treat (ITT) or modified intention-to-treat (mITT) analysis was defined as primary, while per protocol (PP) analyses were also planned as secondary or confirmatory analyses. In 14 (48%) studies, the mITT and PP analyses were considered co-primary. In only one of the protocols we reviewed was the PP analysis considered primary; in one other, no specification was made (although in this case we did not have access to the trial SAP).
The duration of experimental treatment regimens ranged from 13 weeks to 26 weeks for DS-TB trials, and from 24 to 44 weeks for DR-TB trials. Duration of post-treatment follow-up was of varying lengths, these might be measured as time post-randomization or post-treatment, sometimes in weeks, at others in months. Some protocols specified “time windows” around evaluation dates, while others cited only the week or month representing the end of follow-up without explanation as to how much time before or after defined the follow-up “window.” Total trial duration time from randomization to end of follow-up ranged from 78 to 130 week for DS-TB trials, and from 104 to 132 weeks for DR-TB trials. In general, the primary trial outcomes were measured at the end of follow-up. At the time of writing, 8 (26%) trials were still open to enrollment. Seven trials (19%) were complete with study findings not yet available or in follow-up, and 2 (6%) were completed and had results posted on clinicaltrials.gov. For 14 (45%) trials, the primary results of the trial had been published in a peer-reviewed journal or presented at an international conference.
Outcome Definitions
Outcomes across study protocols were assigned to one of three broad categories: Favorable, Unfavorable, or Not Assessable. Protocols generally defined an outcome as Favorable in terms of timing of culture conversion and required number of negative cultures at the end of the follow-up period. Similarly, determination of an outcome as Unfavorable primarily involved the observation of a specific number of positive cultures with or without reference to a time frame for the samples. All protocols specified these bacteriological conditions to some degree, although the circumstances under which determinations were made, and the granularity with which these were defined in individual protocols, varied considerably (see Supplemental Table 1 for a listing of outcome definitions found in protocols). Protocols from recent studies were more likely to allow for categorization of an outcome as Not Assessable if it could not be clearly classified as Favorable or Unfavorable, e.g., deaths unrelated to TB, recurrence due to re-infection with a different strain, and loss-to-follow-up with last culture negative. However, in some cases identical outcome-determining events were categorized as Not Assessable in some cases and Unfavorable in others. Protocols from earlier trials seldom specifically labeled an outcome Not Assessable, although this designation sometimes could be inferred from descriptions of patients excluded from analyses. In others, however, this possibility was neither explicitly nor implicitly addressed. Outcomes determined to be Not Assessable will be discussed simultaneously with Unfavorable outcomes, since the same event could be interpreted as one or the other by different trial protocols. Table 2 summarizes the range of outcome definitions and the frequency of their occurrence across protocols.
Protocols additionally addressed issues around treatment and adherence with respect to categorization of outcome. These will be considered last, as they often coincide with or contribute to other reasons of categorization of outcomes as either Unfavorable or Not Assessable.
Favorable Outcomes
In contrast to Unfavorable and Not Assessable outcomes, Favorable outcomes received the most consistent treatment across protocols. In all protocols that we reviewed, a patient with a Favorable outcome was defined as one who tested negative on a varying number of cultures, with reference to the end of treatment and/or follow-up. Nonetheless, this seemingly straightforward outcome underwent a multitude of permutations across trials. Some trials required only that a patient be “culture negative;” others defined an outcome as Favorable based on a single negative culture. The majority of trials required at least two negative cultures, and in a small number of trials, a patient was required to have three negative cultures to achieve negative status. In addition to the variability in number of negative cultures required, Favorable status was conditional on a variety of restrictions in terms of timing (with reference to either the end of treatment, the end of follow-up or both), spacing (amount of time between the negative cultures that ranged from occurrence on different days to requiring at least four intervening weeks between negative cultures), and culture medium type (solid or liquid).
Spontaneous sputum production usually decreases or resolves during successful treatment and follow-up for TB and most such patients are culture-negative for M.tb(16). A smaller number of studies addressed a patient’s potential inability to produce sputum at various points in the trial as indicative of a Favorable outcome. One protocol interpreted a patient’s inability to ever produce sputum as a Favorable outcome; another further stipulated that never producing sputum would be considered Favorable even if the patient never achieved culture negative status but completed follow-up without clinical or microbiological relapse. Others defined circumstances under which failure to produce sputum at the end of the follow-up period could be classified as negative, e.g., provided this coincided with a patient having prior culture negative status or lacking clinical symptoms. In only one trial was failure to produce sputum at the end of follow-up categorized as an Unfavorable outcome. While generally classified as a Not Assessable outcome (see below), one study classified patients who developed an infection with a strain different from that with which they had originally been infected (an exogenous reinfection) as having a Favorable outcome if the original strain was shown to have been cured. In another, a contaminated culture result or one which could not be evaluated was categorized as Favorable, provided there were no positive cultures at the end of follow-up. Two studies allowed for a patient to have had a Favorable outcome even with a culture at the end of follow-up that was inconclusive, if clinical and radiological symptoms were supportive of the assessment.
Unfavorable Outcomes vs. Not Assessable Outcomes
In the broadest sense, we found that all the reviewed protocols deemed that a patient’s outcome would be considered Unfavorable primarily based on positive sputum cultures. However, the level of detail attached to culture positivity varied from the most general (“Failure at end of treatment”) to the bewilderingly complex: in one trial, for example, the outcome of a patient not attending the final visit could not be categorized as Unfavorable until all of four specified conditions were met, and two additional conditions had been taken into account.
Categories of unfavorable/not assessable outcomes
Failure to ever achieve negative culture conversion. A patient’s failure to respond successfully, as defined bacteriologically, to the prescribed regimen by the end of the treatment period constituted the most straightforward type of unfavorable outcome. In some protocols, however, the treatment duration could be extended if necessary or if some limited number of treatments had been missed, thus lengthening the time a patient was given to achieve culture conversion or culture negative status.
Relapse and Re-infection. Recurrence of bacterial infection can occur as an endogenous relapse, defined as a patient’s recurrence with positive culture status with the originally diagnosed strain, having previously attained negative status, or as an exogenous re-infection, i.e., a new infection with a different strain. Not all protocols specifically addressed an analytical approach to both. One protocol did not address either relapse or reinfection; some categorized the status of relapse but not re-infection, and several addressed re-infection but not relapse. Other protocols addressed and categorized both.
Relapse. In all studies, relapse was considered an Unfavorable outcome in terms of its analytical treatment. Although some studies provided specific definitions of relapse, others included it as either part of a composite outcome or (in a few cases where patients were required to have been previously treated and cured prior to the study) as the primary outcome. Definitions, when provided, varied as to when and how relapse was defined, and with what level of detail, however. Some studies defined a relapse as occurring in patients who were culture-negative at the end of treatment, but with different constraints on the conversion to culture-positive. These included diagnosing relapse in a patient who tested positive twice with no intervening negatives, whose two positive tests occurred at least one day apart, who had positive sputum cultures during four consecutive monthly exams (at least one with 20 or more colonies), or who had a subsequent diagnosis and treatment for the same or another DR strain (in a study targeting DR infections). Similarly, two additional DR studies defined relapse as having occurred when a patient was prescribed a new DR regimen after treatment and before the end of follow-up. Another study specified that a patient’s conversion to negative status had to occur over at least four weeks, with subsequent positive status (on solid medium) confirmed by a second positive culture on a different day. Other studies offered less specific criteria, including simply “recurrence by the end of the study,” “after cure, single culture positive,” and “one culture positive and clinical features suggestive of recurrent disease.”
Reinfection. Unlike relapse, patients who acquired an infection with a different type of TB were regarded by most DR-TB and DS-TB studies as having outcomes that were Not Assessable. Only one protocol viewed re-infection with a different strain as Unfavorable; one study targeting patients with DR-TB categorized re-infection with a different DR strain as Unfavorable, but with a DS strain as Not Assessable. As previously mentioned, one protocol categorized a patient’s re-infection as Favorable if occurring after a confirmed conversion to negative status with respect to the original strain.
Death. With varying degrees of granularity, most protocols addressed death as an outcome, whether occurring during treatment, after treatment during the follow-up period, or during either. One protocol did not mention death in relation to outcome, and another mentioned death only in that it precluded a Favorable outcome; we were unable to obtain SAPs for either of these studies. The death of a patient was generally categorized as an Unfavorable outcome, although under certain specified circumstances, deaths could also result in study outcomes being considered Not Assessable.
Death during treatment. A patient’s death during treatment could fall into one of the following categories: (1) death due to any cause, (2) death directly related to TB, and (3) death due to causes unrelated to TB. Non-TB deaths were categorized differently across studies; some considered these to be Not Assessable, while more frequently, studies treated them as Unfavorable, with the exception of deaths due to accident, violence, trauma or suicide (with the exception of suicide, these latter were generally classified as Not Assessable). Death by suicide was specifically addressed in a third of the protocols, but was considered by some as Unfavorable, and by others as Not Assessable. An additional protocol specified that the outcome of a patient whose death during treatment was unrelated to TB, but whose culture status at the time of death was unknown, would be classified as Not Assessable.
Death during post-treatment follow-up. During the post-treatment follow-up phase, “all cause deaths” (without further differentiation) were regarded as Unfavorable outcomes in some studies, while in others, deaths were only considered Unfavorable if TB-related. A small number of studies considered a generalized category of non-TB deaths to be Not Assessable for purposes of analysis. In several studies, the treatment of death during follow-up was determined with respect to bacteriological status. Several trial protocols classified the outcomes of patients who died with their last culture negative as Not Assessable. Additional studies more specifically proposed that deaths be considered Not Assessable only if a patient died while culture negative, under the condition that the last positive culture had been followed by two negative cultures at least seven days apart. In addition, one study specified that a patient who died from extrapulmonary TB would be considered as having an Unfavorable outcome; another classified patients whose deaths were due to an infection other than with the originally diagnosed strain to have outcomes that were Not Assessable.
Withdrawal of consent/ lost-to-follow up. Across study protocols, outcomes of patients who were lost to follow-up or who withdrew from the study appeared to be the most challenging to categorize. These patients were variously noted as having been lost to follow-up or withdrawn: (1) while still being treated; (2) at any point, during follow-up, (3) after being cured at the end of treatment, during follow-up, or (4) “when last seen.”
During the treatment phase. With respect to patients lost or withdrawn while treatment was still ongoing (without further caveats), a quarter of the protocols classified their outcomes as Unfavorable; one study alone categorized them as Not Assessable. Other protocols determined categorization based on the reason for the patient’s withdrawal. In one protocol, patients who withdrew or were lost due to clinical reasons were considered to have an Unfavorable outcome. More frequently, patients who exited the study during the treatment phase were considered to have outcomes that were Not Assessable, including those whose withdrawal was either unrelated to TB or was due to protocol violation, pregnancy, or moving away and/or becoming untraceable at any point.
After treatment completion. In addressing patients who were lost to follow-up or who withdrew after completing treatment, Unfavorable outcomes could include those who exited the study under any circumstances (although one protocol classified such a patient as having an outcome that was Not Assessable); those whose last positive culture was not followed by at least two negative cultures ≥7 days apart; those who terminated the study early, but were known to be alive at last contact, or who were lost to follow-up with vital status unknown; patients who had not achieved culture negative status or who had been classified as having an Unfavorable outcome before their withdrawal; patients who could not be contacted for some specified period of time prior to the last study visit; and those who had no culture results within a specified window of time prior to the study endpoint. As specified by two protocols, it was also necessary for these latter patients to be either culture positive when last tested, have no other post-baseline results, or have a negative culture at their most recent result, but with radiological or clinical symptoms that were inconclusive.
Alternatively, the following patients were categorized with varying frequency as having outcomes that were Not Assessable: those whose last culture before study exit was negative; patients whose last two culture results prior to exit were negative, who had not otherwise been deemed Unfavorable; patients whose last culture was negative and whose last positive culture was followed by at least two negative cultures at different visits ≥7 days apart, without an intervening positive culture; and patients not otherwise classified as Unfavorable prior to exit from study.
Patients who withdrew or were lost to follow-up after having been cured at the end of treatment were specifically addressed by one study; those who either did so with their most recent culture positive or who moved away with their most recent culture positive were considered to have Unfavorable outcomes, while those who under the same circumstances were culture negative or whose most recent culture was contaminated were categorized as Not Assessable.
In some protocols, outcomes were defined at the time when patients “were last seen.” Detailed events included being culture positive, being culture positive with the same type (whether confirmed or not), culture positive not followed by two negatives, or simply not having achieved or maintained culture negative status at the time of their last visit (prior to study endpoint).
Treatment-Related Issues (including treatment changes for adverse events)
Most protocols addressed to some extent their analysis plans regarding treatment issues, including extension, restart, change, and discontinuation of the medications which comprised the specific study regimens. Although in most cases patients who experienced treatment disruptions were considered to have unfavorable outcomes, details varied considerably from study to study. A patient whose treatment was extended for any reason was considered to have had an unfavorable outcome by one study. More commonly, however, the outcomes of patients whose treatment was extended were considered Unfavorable but with exceptions that were considered Not Assessable, including: temporary drug re-challenge, over-treatment with assigned drugs, ≤21 days non-study anti-TB meds for active TB, secondary isoniazid preventive therapy in HIV+ patients, re-infection, pregnancy, making up missed doses, and remaining on treatment at the end of the study without having been declared a treatment failure.
Some protocols categorized patients whose treatment had to be restarted as experiencing an Unfavorable outcome, again with the exceptions that they either had been infected with a different TB type in some cases or had become pregnant in others; another protocol limited designation of an Unfavorable outcome to the period after completion of treatment but before the study’s end.
A change in treatment can take many forms, and this was reflected across protocols. A patient who had any change of medication frequency or dose (except in the case of re-infection) was usually considered as having an Unfavorable outcome, although two protocols made exceptions for patients with a single drug replacement, or those whose drug replacement was due to a guideline change in the standard of care group (neither affected outcome classification). Patients whose treatment was changed due to clinical or radiological deterioration, or because of non-response or poor adherence, were considered to have an Unfavorable outcome by one study each, respectively. Several studies considered as Unfavorable outcomes those of patients for whom one drug was replaced or added, while other studies required that a patient’s treatment involve the replacement or addition of at least two drugs. Such categorization based on number of drug changes ranged from the simple to the overly complex: one study placed further conditions on a two-drug change, declaring that it defined a patient’s outcome as Unfavorable if this occurred because the patient (1) had not converted by the end of the first (more intense) phase of treatment, (2) had bacteriologically reverted during the second treatment phase after having converted to negative in the first, (3) had evidence of additional acquired resistance to fluoroquinolones or 2nd line injectables, or (4) had not converted their sputum cultures to negative status and had two positive cultures during a specific time period, with the caveat that if one or more of the samples were unavailable or contaminated this would be considered culture positive if the patient displayed deteriorating clinical symptoms.
A patient whose treatment was discontinued was considered by various protocols as having an Unfavorable outcome if study treatment was halted for reasons including the following: experiencing a serious adverse event; starting a different DR-TB regimen; failing to convert after the first phase of a trial where the treatment regimen occurred in two phases, or because the trial regimen needed to be significantly modified for some (unspecified) reason. In most trials, study treatment was discontinued in patients who became pregnant during therapy, who were then treated with standard therapy. In some trials, patients who discontinued treatment because they became pregnant were considered to have an outcome that was Not Assessable, while in others a patient’s outcome was considered Not Assessable if the patient’s last culture was negative, but Unfavorable if it were positive.
Incomplete treatment in patients whose culture status could not be evaluated at the end of follow-up was considered Unfavorable in several studies; an additional protocol defined a patient’s outcome as Unfavorable if, in addition to incomplete treatment, a patient had not attained culture negative status by the end of follow-up. The effect of a patient’s missing drugs during the treatment phase was addressed by one protocol that considered this to be Unfavorable if some or all drugs were missed regularly, or if all drugs were missed for more than two consecutive weeks.
Patients who took TB-related but off protocol drugs, or who started TB treatment outside of the study with the most recent culture positive, were considered by one study to have an Unfavorable outcome, while off-protocol drugs not related to TB rendered the outcome Not Assessable. In two other studies, only patients taking specific off-protocol drugs were categorized as having Unfavorable outcomes.