The aim of this investigation was to evaluate whether the relative change in renal clearance due to ibuprofen administration depends on the gestational age (GA). Clearance of amikacin was used as a surrogate marker for renal clearance in preterm infants (GA 24-34 weeks, day 1) on respiratory support. Clearance in infants co-treated with ibuprofen was compared to that of infants not co-treated with ibuprofen. Absolute change of clearance in four consecutive cohorts of increasing (<27, 27-28, 29-31, 32-34 weeks) GA and linear correlations of clearance on GA were calculated in both groups. Data were collected from 204 infants, of whom 93 were co-treated with ibuprofen. Mean amikacin clearance was lower (0.48 to 0.59 ml/kg/min, P <0.001) in infants co-treated with ibuprofen. Absolute decrease in mean amikacin clearance (0.10 to 0.14 ml/kg/min) was similar in all four cohorts. Linear correlations of clearance with GA were documented in infants co-treated (y =0.21+0.011x) or not co-treated (y =0.44+0.009x) with ibuprofen. Renal clearance, reflected by amikacin clearance, is decreased by ibuprofen in preterm infants of 24 to 34 weeks GA on respiratory support on the 1st day of life, independent of the GA.