Across four Latin American countries, 29% of patients with MDD were resistant to treatment, with TRD prevalences of 21% in Mexico, 32% in Colombia, 33% in Argentina, and 40% in Brazil. In comparison, the STAR*D trial, which enrolled patients with MDD who were candidates for medication as a first treatment step, found that approximately one-third of patients with MDD in the United States were treatment-resistant . Other estimates of TRD in the United States have been lower (7%–12%), though, unlike TRAL, diagnosis of MDD and TRD was determined using a retrospective claims database [21, 22]. In Europe, a large multicenter study (European Group for the Study of Resistant Depression) found a TRD prevalence rate of 41% among patients with MDD, while a UK study of patients being treated for MDD in a primary care setting found that as many as 55% had TRD [12, 23]. Prevalence rates of TRD in other geographic regions have been estimated at 22% of patients in Canada receiving antidepressant treatment for MDD from a primary care physician; 21% of patients in Taiwan with new-onset, pharmaceutically treated MDD; and 12% of patients in Japan with new-onset, pharmaceutically treated MDD during a 1-year period of time [24,25,26]. Importantly, definitions of TRD varied across these studies, limiting direct comparison. The variation in TRD prevalence by country is further discussed below, but it is notable that there may be greater reluctance to report and seek treatment for depression and, by extension, TRD, among patients in East Asian countries.
In this interim analysis of TRAL, while the prevalence of TRD was similar in private and public sites of care overall, numerical differences were observed in some countries. In Colombia, 35% of patients in private settings had TRD versus 24% of patients in public settings; in contrast, in Brazil, 17% of patients in private settings had TRD versus 45% of patients in public settings. The higher prevalence of TRD in Brazilian public settings could be due to the nature of these public services, most of which are university-based research centers, with a greater demand from higher-complexity and more severe patients; however, further information is needed to confirm this assumption. When sites of care were examined in more detail among all patients with MDD, the site with the highest prevalence of TRD was the general hospital setting (60%). Notably, variability in access to healthcare may limit comparisons across countries. Variability in the types of care settings that participated in the current study may also limit interpretation of these results.
This interim analysis identified several concerning demographic characteristics of patients in Latin American with MDD. The mean age at which MDD was diagnosed was 37.9 years overall, 38.2 years for patients with non-TRD, and 37.3 years for patients with TRD, suggesting that earlier diagnosis of MDD in Latin American countries is important. Earlier diagnosis could lead to earlier treatment, better outcomes for patients, and potentially a decreased burden of disease for patients and caregivers . Additionally, more women than men were diagnosed with MDD. This is consistent with global reports of depression prevalence that have demonstrated that female sex is a significant risk factor for depression .
Previous studies have found higher hospitalization rates and lengths of stay for patients with TRD compared to those with non-TRD [9, 13]; however, no such associations were observed in the interim analysis of the current study. This finding may reflect economic and cultural differences between Latin America and higher-income countries. In Latin America, patients with MDD may face external challenges accessing mental healthcare, as well as stigma associated with seeking care for mental health. Moreover, it is important to note that the current analysis includes only data from the baseline study visit, and hospitalization information was taken retrospectively. Healthcare resource utilization will also be evaluated in the 1-year longitudinal phase of TRAL; follow-up during this phase will include direct collection of hospitalization information and thus may provide more accurate information than that collected in Phase 1.
A higher mean MADRS total score was observed in the TRD group (29.4; SD: 7.9) than in the non-TRD group (23.3; SD: 11.2). Among patients with TRD, 87% had moderate or severe depression; however, the relatively high proportion of patients with TRD who were classified as having moderate depression (61%) compared to severe depression (26%) was surprising. This indicates that the greatest proportion of unmet need for patients in Latin America with TRD may be in treatment of moderate depression.
Based on current disease status items and the MINI, numerous factors were significantly more common among patients with TRD versus non-TRD, including suicidality and anxiety. This is in agreement with other published data; a large European multicenter study showed an association between suicidality and treatment resistance , and other studies have demonstrated associations between TRD and comorbid anxiety disorders [29, 30]. A systematic review of socio-demographic and clinical predictors of TRD found that a current or lifetime diagnosis of generalized anxiety disorder was predictive of nonresponse to depression treatment, while anxious symptoms, irrespective of a diagnosis, influenced remission from depression . Further, the presence of more than 1 anxiety disorder in a single patient is also associated with TRD .
Compared to patients with non-TRD, numerically higher proportions of those with TRD had taken a previous psychiatric medication or were currently receiving relevant psychiatric therapy. Use of numerous classes of treatment were observed among patients with TRD, although therapies such as brain stimulation techniques (1%) and ketamine/esketamine (< 1% current use; 2% previous use) were low, potentially due to difficulty accessing them. Notably, for some treatment classes, many patients had missing data (the exact number varied by treatment class). This is likely due to patients not remembering previous treatments or the correct dates or doses of previous treatment regimens.
While TRD has been associated with increased healthcare resource utilization [9, 31], the only significant difference observed in the current study was a higher number of psychiatrist consultations for patients with TRD in comparison to non-TRD. As discussed previously, this may be due, at least in part, to difficulty of access and cultural sensitivities around seeking help for mental health issues in Latin America. As expected based on previous studies [9, 10], patients with TRD demonstrated significantly greater work impairment than patients with non-TRD on most WPAI:D items.
One of the strengths of this study is the quality of the diagnosis of MDD, which was defined, in part, using the semi-structured interview, MINI. Many TRD studies have defined MDD using presumptive diagnoses from patient registry databases of public or private health services. This more direct MDD diagnosis ensures a more uniform study population and thus the potential to detect more subtle differences between groups. Importantly, the present analysis represents baseline results; further information will be reported upon study completion.
The present study is not a population-based survey, as it included only individuals being assisted in clinical services (clinics, hospitals, community services) that treat mental disorders, independent of whether they are specialized or not. This could be perceived as a limitation for a prevalence study, considering that many cases of depression go undiagnosed in a general medicine setting. However, it was the authors’ decision to investigate the prevalence of treatment resistance among those diagnosed with MDD and to investigate predictors of TRD and differences between TRD and non-TRD populations.