A shortened 30-day course of benznidazole taken once daily matches the efficacy of standard 60-day treatments for chronic Chagas disease while dramatically reducing adverse side effects, according to findings from the TESEO clinical trial published in The Lancet Infectious Diseases.
Transforming Chronic Parasitic Care Through Shorter Dosing Schedules
A shorter and simpler drug regimen could reshape how chronic Chagas infection is treated globally. The TESEO trial—a large randomized clinical study co-led by the Barcelona Institute for Global Health (ISGlobal), supported by the “la Caixa” Foundation, alongside the University of Texas at El Paso (UTEP) and the Bolivian health organization CEADES—discovered that benznidazole taken once a day for 30 days is just as effective as the current standard of care while producing markedly fewer side effects.
According to the published findings, a treatment established over half a century ago can now be safely shortened. This change potentially removes one of the biggest obstacles preventing infected individuals from ever being cured. Trypanosoma cruzi, the parasite that causes Chagas disease, infects more than seven million people worldwide. The heaviest burden remains concentrated in Latin America, but modern migration and travel patterns have turned the infection into a broader public health concern across the United States, Europe, and Japan.
In Plain English: The Clinical Takeaway
- Reduced Pill Burden: Patients take benznidazole once daily for 30 days instead of the traditional twice-daily schedule for 60 days.
- Better Tolerability: Side effects like skin rashes, nausea, and digestive issues dropped by roughly 40%, boosting treatment completion rates.
- High Parasite Clearance: Quantitative PCR (polymerase chain reaction) blood tests showed a 94% sustained clearance rate three years post-treatment, matching standard-course outcomes.
Overcoming Historical Barriers to Adherence and Treatment Completion
Although the parasite often remains clinically silent for years, roughly 30 to 40 percent of infected individuals eventually develop Chagas disease. This progression can lead to serious and potentially life-threatening cardiac or gastrointestinal complications. Despite the scale of the crisis, fewer than one percent of infected people are ever diagnosed and treated. This massive treatment gap is driven by weak screening programs, social stigma, and the poor tolerability of existing therapeutics.
Only two pharmacological agents exist against Trypanosoma cruzi: benznidazole and nifurtimox. Both were developed in the 1960s and 1970s, and both are traditionally administered using dosing schedules that have barely changed since their inception. The standard benznidazole course requires patients to take the drug twice a day for 60 days. This regimen represents a demanding commitment for patients living far from clinics or holding jobs that make midday dosing difficult.
More importantly, these prolonged regimens frequently trigger adverse reactions ranging from dermatological and digestive complaints to neurological symptoms. As a result, up to 31 percent of patients abandon treatment before finishing it. Because full treatment completion is essential for clearing the infection, side effects and high pill burdens translate directly into population-level treatment failures.
Inside the TESEO Trial Design and Execution
The TESEO trial was designed to test whether alternative durations and dosing schedules could improve this clinical equation. Igor Almeida of the University of Texas at El Paso served as a corresponding author and co-senior author alongside Faustino Torrico of CEADES and Joaquim Gascón of ISGlobal. According to the research team, this investigation marks the first randomized clinical study to evaluate benznidazole and nifurtimox head-to-head under identical conditions, complete with a three-year patient follow-up utilizing quantitative PCR to detect parasite DNA in the blood.
This prolonged observation window is critical because the parasite can persist at extremely low levels after treatment. Confirming sustained clearance requires rigorous molecular monitoring that many earlier studies could not provide. The phase 2b trial enrolled 450 adult participants at three medical centers in Bolivia, a nation where Chagas infection remains highly endemic and where the research team maintains decades of clinical experience.
Participants were randomly assigned to one of six treatment groups. Three groups received benznidazole under varying schedules: the 60-day standard regimen, a shortened 30-day course, or an extended 90-day course. Three parallel groups received nifurtimox evaluated across the same three schedules. Throughout the multi-year study, investigators documented every drug-related adverse event and periodically tested blood samples using sensitive molecular techniques.
| Regimen Type | Dosing Schedule | Adverse Events (%) | Treatment Completion (%) | 3-Year Parasite Undetectable (%) |
|---|---|---|---|---|
| Standard Benznidazole | 2 pills daily for 60 days | 60% | 60% | 95% |
| Shorter Benznidazole | 1 pill daily for 30 days | 37% | 83% | 94% |
| Extended Benznidazole | 1 pill daily for 90 days | Data comparable | Varies | Evaluated |
Data from the trial demonstrated that only the 30-day benznidazole regimen significantly reduced adverse side effects. While 60 percent of participants experienced a drug-related adverse event on the standard regimen, only 37 percent experienced side effects on the 30-day course—representing a roughly 40 percent reduction in adverse reactions. Furthermore, 83 percent of patients in the 30-day group completed their treatment without interruption, compared to just 60 percent in the standard group. Most adverse events appeared within the first two weeks regardless of duration, and almost all resolved successfully.
Three years post-treatment, the parasite remained undetectable in the blood of 94 percent of participants in the 30-day benznidazole group, closely mirroring the 95 percent clearance rate observed in the standard group. This demonstrated the non-inferiority of the shortened course. According to Joaquim Gascón, the improved safety profile and once-daily dosing schedule hold the potential to substantially increase the proportion of patients who complete therapy. Faustino Torrico noted an additional logistical advantage: the 30-day course uses a quarter of the total drug volume, allowing clinics to treat four patients with the same medication supply previously required for one.
The seven-year trial was funded by an approximate $8 million award from the National Institute of Allergy and Infectious Diseases, with partial operational support from UTEP’s Border Biomedical Research Center (BBRC). Marc Knecht, dean of the UTEP College of Science, noted that the trial represents a landmark achievement as the first clinical trial sponsored directly by the university.
The Path Forward for Global Chagas Control
References
- Torrico, F., Gascón, J., Almeida, I., et al. (2026). Efficacy and safety of shorter benznidazole and nifurtimox regimens for chronic Chagas disease (TESEO trial). The Lancet Infectious Diseases.
