Objective: This exploratory study assessed the safety of the combination of sulfamethoxazole, trimethoprim and guaifenesin (STG) in adult and pediatric patients with acute bronchitis according to local labelling in Peru. Results: We enrolled 51 pediatric and 52 adult participants diagnosed with acute bronchitis and indication of STG. The mean ages were 7.6 years (SD ± 3.2 years) and 42.8 years (SD ± 16.1) and the proportion of female patients were 51% and 65%, respectively. The duration of treatment in pediatric patients was < 5 days in 2% of patients, 5 days in 13.7%, 6-7 days, in 82.4% and > 7 days in 2% while in adults patients it was < 5 days in 17%, 5 days in 69.2%; 6-7 days in 28.8% of patients. Adverse events (AEs) were registered in 9.6% and 19.2% of pediatric and adult patients, respectively. These AEs had definite relation of causality with the study drugs in 2 adults (20% of AEs) and possible causality with the study drugs in 4 pediatric (80% of AEs) and 2 adult cases (20% of AEs). Our results provide valuable data to develop trials of pharmacovigilance where different statistical parameters should be considered to calculate an adequate sample size in studies evaluating STG in pediatric or adult patients. Trial registration NCT02879981 and NCT02902640