Objective:To study the efficacy and safety of oral acetaminophen or high-dose ibuprofen as rescue treatment after failure of conservative management in very preterm infants (VPIs) with haemodynamically significant patent ductus arteriosus (hsPDA).Methods:From May 2020 to November 2022, VPIs with hsPDA (gestational age<32 weeks and age 4~6 d) admitted to NICU of our hospital were prospectively enrolled. The rescue treatment was initiated if hsPDA still exist after 3~4 d of conservative management. The infants were randomly assigned into acetaminophen group (oral acetaminophen 15 mg/kg, once every 6 h for 3 d) and high-dose ibuprofen group (oral ibuprofen 20 mg/kg for the first dose, 10 mg/kg each dose after 24 h and 48 h). Before and after rescue treatment, the following were recorded: echocardiography, complete blood count, biochemistry, B-type natriuretic peptide (BNP), fecal occult blood test (FOBT) and transcranial Doppler ultrasound. Urine output and complications were also examined. SPSS 20.0 was used for statistical analysis.Results:A total of 36 cases were in the acetaminophen group and 37 in the high-dose ibuprofen group. The two groups showed similar efficacy as rescue treatment [80.6% (29/36) vs. 78.4% (29/37), P>0.05]. No significant differences existed in the incidences of upper gastrointestinal bleeding, positive FOBT, oliguria, stage Ⅱ-Ⅲ necrotizing enterocolitis and stage Ⅲ-Ⅳ intraventricular hemorrhage between the two groups ( P>0.05). After rescue treatment, the serum cystatin C in high-dose ibuprofen group was higher [(1.72±0.29) mg/L vs. (1.58±0.26) mg/L] and 24-hours urine output was lower [(3.1±1.0) ml/(kg·h) vs. (3.7±0.7) ml/(kg·h)] than the acetaminophen group (all P<0.05). No significant differences existed in serum creatinine, platelet count, BNP, alanine aminotransferase and total serum bilirubin between the two groups ( P>0.05). Conclusions:After failure of early conservative management in VPIs with hsPDA, when initiated within 7-10 d after birth, rescue treatment with oral acetaminophen or high-dose ibuprofen has a similar efficacy of 80%, and both drugs are safe. Oral high-dose ibuprofen may have a greater effect on renal function than acetaminophen.