Background Essential surfactant properties include transfer to gas-liquid interface, reduction of surface tension and film replenishment during respiratory cycles.

Objective To compare component-specific film formation properties of infant and therapeutic surfactants.

Design/methods Using a multiwell fluorescence assay, we compared maximal fluorescence (Max), time to reach Max (tMax) and phospholipid concentration for ½ maximal signal (½Max) for calfactant (CAL), poractant (POR), beractant (BER), colfosceryl palmitate (COL), with surfactant from immature infants with RDS. Dose-response studies were performed for addition of SP-B, albumin and budesonide.

Results Max and ½Max values for CAL were higher/similar to those of rat surfactant. There were significant differences between CAL and other therapeutic surfactants for Max (CAL >COL >POR >BER) whereas ½Max were similar except for COL.

In surfactant from 39 infant tracheal aspirates, ½Max was inversely correlated with SP-B content (p = 0.001). Addition of SP-B to samples with low endogenous content (<0.1%) decreased ½Max in a dose-dependent way. Addition of 1.25% SP-B to BER (SP-B content 0.04%) increased Max by 324%. Addition of albumin to CAL (0.75 μg/μg PL) increased ½Max by 110% and reduced Max by 13%. By contrast, addition of budesonide to CAL at 2% and 10% increased Max by 51 ± 26% and 93 ± 19%, with no effect on ½Max.

Conclusions This assay reveals differences in film formation efficiency for therapeutic surfactants reflecting differences in SP-B content and lipid composition. Film formation by infant surfactant is strongly influenced by SP-B content. The findings support the key physiological role of SP-B and the safety of surfactant as anti-inflammatory drug vehicle.