Further Investigations on the Ileum Model as a Possible Alternative to In Vivo Eye Irritancy Testing

Summary

The concentration of six surfactants required to block spontaneous contractions of rabbit isolated ileum by 50% (EC50) correlated well with in vivo eye irritancy (correlation coefficient -0.996) only when fresh ileum was tested at 35°C. Storage of ileum for 2 hr or 4 hr before testing did not significantly alter the potency of five of the surfactants, but the potency of triethanolamine decyl sulphate (TDS), the only C-10 surfactant tested, was significantly reduced as compared to fresh controls. When tested on fresh ileum at 29°C all the surfactants, except TDS, were more potent at blocking contractions while TDS was significantly less potent.

It is suggested that the penetration barrier to surfactants is considerably more complex than previously envisaged, possibly involving a transport system capable of concentrating TDS, but not the other agents tested.

It would appear that, provided experimental conditions are carefully controlled, the ileum model can yield results which correlate well with in vivo ocular irritancy and as such may provide the basis for the development of a viable screen for irritancy of surfactants and surfactant-based products.