Importance Off-label treatment was common for ophthalmia neonatorum because only erythromycin ointment had been approved by the US Food and Drug Administration (FDA) for this indication. Ophthalmia neonatorum was previously considered a different indication from bacterial conjunctivitis in older children and adults because of uncertain similarities in the cause of disease and the treatment course between the 2 populations. Prospective therapeutic clinical studies were required to demonstrate the effectiveness of treatment for ophthalmia neonatorum. Objective To review the therapeutic clinical trials for patients with bacterial conjunctivitis to evaluate the similarity in the cause of disease and the treatment response between neonates and older children and adults. Design, setting, and participants In this comparative effectiveness research review of pooled data from the most recent 30 bacterial conjunctivitis trials (N = 2018) submitted to the FDA to support the approval of topical ophthalmic solutions for older children and adults, 95% CIs were constructed from clinical cure rates. Cure rates in 3 neonatal randomized clinical trials (N = 392) of patients treated with ophthalmic anti-infective solutions of ciprofloxacin, gatifloxacin, and moxifloxacin were constructed and compared. The baseline ocular swab cultures were analyzed. Main outcomes and measures Cure rates of neonatal trials were compared with the 95% CIs among older children and adults. The bacterial organisms isolated from these 2 populations were compared. Results The 3 neonatal trials enrolled a total of 392 patients, and the 30 trials of older children and adults enrolled a total of 2018 patients. Neonatal clinical cure rates for moxifloxacin (day 4, 48%), ciprofloxacin (day 4, 49%; day 5, 61%), and gatifloxacin (day 7, 79%) were within the 95% CI for products approved to treat older children and adults with bacterial conjunctivitis. Bacterial organisms were consistent between these 2 populations. Conclusions and relevance Comparison of the pooled analysis of these historical trial data suggests similarity in the cause of disease and the treatment response between neonates and older children and adults with bacterial conjunctivitis. Therefore, it was appropriate to extrapolate the effectiveness from older children and adults to neonates to support the approval of therapies for ophthalmia neonatorum. Based on this analysis, ophthalmic solutions of ciprofloxacin, gatifloxacin, and moxifloxacin are now approved for all age groups. This analysis presents an approach of using pooled data from previously underpowered individual trials to establish the similarities in the cause of disease and in treatment response between children and adults, which are the fundamental elements used to evaluate whether extrapolation of effectiveness can be used to support drug approval.