To examine safety and pharmacokinetics of multiple dose IT rhSOD in premature infants with RDS, 33 infants (700-1300g) were studied. Infants were randomized and blindly received saline, 2.5mg/kg or 5mg/kg rhSOD IT (in 1-2 ml/kg of saline) within 2 h of surfactant administration. Infants were treated every 48 h (while endotracheal intubation was required) up to 7 doses. CBC, chemistries, chest radiographs, neurosonograms, SOD concentration and activity measurements (tracheal aspirates-TA, serum, urine) and TA inflammatory markers were assessed throughout the 28 d study. SOD concentrations in serum (90[55/147]- geometric mean with lower/upper confidence intervals), TA (317[220/458]) and urine (328 [242/444] ng/ml were similar at baseline in all 3 groups and did not change significantly in the placebo group. In the rhSOD treatment groups, SOD concentrations were increased when measured on day 3 and did not change signficantly thereafter over the 14 day dosing period. SOD concentrations averaged 194 [133/283] in serum, 830 [601/1146] in TA and 990[833/1287] ng/ml) in urine for the low dose group and 233 [159/343] in serum, 1239 [678/2262] in TA, and 1391 [1059/1827] ng/ml in urine for the high dose group (p<0.05,ANOVA). Activity of the enzyme correlated well with concentration (rhSOD was active even when excreted in urine). TA neutrophil chemotactic activity (a marker of lung injury) was lower in the rhSOD groups compared to placebo. TA albumin concentration was lower in the high dose rhSOD group compared to the other 2 groups. Two infants died during the study period(1 placebo, 1 high dose rhSOD group). One infant in each group developed bronchopulmonary dysplasia (BPD). No significant differences in any other adverse event were noted between groups. These data indicate that multiple IT doses of rhSOD increase activity of the enzyme in TA, serum and urine, reduce TA lung injury markers and appear to be well tolerated. Further clinical trials examining the efficacy of rhSOD in the prevention of BPD are warranted.(Funded by Bio-Technology General Corp.)