Patent ductus arteriosus (PDA), the most common cardiovascular complication of prematurity, is associated with higher mortality and morbidities in extremely low gestational age neonates (ELGANs, \< 27+0 weeks). Ibuprofen and acetaminophen, which act by reducing prostaglandin synthesis, are the most commonly used first and second line agents for PDA treatment across Canada. However, initial treatment failure with monotherapy is a major problem, occurring in \>60% ELGANs. Treatment failure is associated with worsening rates of mortality and bronchopulmonary dysplasia (BPD), while early treatment success can achieve rates comparable to neonates without PDA. Treatment failure resulting in prolonged disease exposure is thought to be a major contributor. Recently, combination therapy with acetaminophen and ibuprofen has emerged as a new treatment regime. Acetaminophen exerts anti-prostaglandin effect through a different receptor site than ibuprofen, providing a biological rationale for their synergistic action. The objective of this study is to evaluate the clinical impact, efficacy and safety of combination regime (Ibuprofen + IV Acetaminophen) for the first treatment course for PDA in ELGANs vs. Ibuprofen alone (current standard treatment).