Background Antimicrobial resistance has become a global health emergency and is contributed to by inappropriate antibiotic use in community clinical settings. The aim of this study was to evaluate the antimicrobial use pattern in infants from birth until 18 months of age in Indonesia. Methods A post-hoc analysis was conducted in 1621 participants from the RV3BB Phase IIb trial conducted in Indonesia from January 2013 through July 2016. Any health events were documented in the trial as adverse events. Concomitant medication surveillance recorded all medications, including antibiotics during the 18 months of follow-up. Information included the frequency, duration of usage, formulation, classes, and their indications, including prophylactic antibiotic and perinatal use. Results Of 1621 participants, 551 (33.99%) received at least one antibiotic for treatment of infections during the 18 months observation period. Additionally, during the perinatal period, prophylactic antibiotics were used in 1244 (76.74%) participants and antibiotics consumed in 235 mothers of participants (14.50%). A total of 956 antibiotic consumptions were recorded for 18 months follow up, 67 (7.01%) as part of antimicrobial combinations. The average duration of antibiotic course was 4.92 days. Penicillin and sulfonamides were the most common antibiotic classes consumed (38.81% and 24.48%, respectively). Conclusions Despite the low community consumption rate, the overuse of antibiotic in URTIs and non-bloody diarrhea in our setting represents a major opportunity for antimicrobial stewardship, particularly in early life.