Pharmacological PDA closure was achieved after 1 or 2 IBU courses in 36 of 56 infants ( 64.3 % ) after bolus administration and in 46 of 55 ( 83.6 % ) after continuous infusion ( p = 0.020 ) , and in 9 of 26 ( 34.6 % ) and 24 of 30 ( 80.0 % ) , respectively , in the infants with a gestational age of 23-27 weeks ( p = 0.006 ) .