Surfactant drugs differ in both phospholipid and protein content and can be categorized as listed in Table 1. Although a complete description of individual surfactant preparations is beyond the scope of this review, differences between classes of surfactants can be briefly summarized. Synthetic surfactants differ most notably from natural surfactants in their protein composition. The original commercially available surfactant, colfosceril palmitate (Exosurf; Glaxo Wellcome), is composed of the phospholipid dipalmitoyl phosphatidylcholine and chemical agents to promote adsorption and spreading; it lacks SPs.
Natural surfactants are derived from animal lungs through a process of organic extraction from either the lipid component of minced lung tissue or from alveolar lavage fluid. SP-A, SP-B, SP-C, and SP-D are present in natural surfactant, and convey dramatic benefits on the ability of natural surfactant to lower alveolar surface tension and modulate lung inflammation in vitro. In clinical trials, natural surfactants have been shown to reduce the risk of pneumothorax more effectively than synthetic surfactant preparations.
Among natural surfactants, Survanta (Abbott Laboratories; Abbott Park, IL), Infasurf (ONY, Inc; Amherst, NY), and Curosurf (Chiesi Farmaceutici SpA; Parma, Italy) are approved for the treatment and prevention of RDS in infants. Although they contain foreign proteins, natural surfactant preparations have not triggered significant allergic responses in treated infants. In 2005, a new-generation synthetic surfactant, Surfaxin (DiscoveryLabs; Warrington, PA), using a novel peptide (KL4) to replace the biophysical properties of natural SPs, received favorable review by the FDA as a treatment for RDS. Final approval is pending.