In vitro and in vivo SPF
The in vitro SPF values for the formulations tested were not significantly different. This may be because of the limitations of the spectrophotometric method in assessing the interactions of the formulations with the skin. This result is based on the total concentration of the ultraviolet filter in the formulations. The in vitro SPF test is rapid and cost-effective, and can estimate the SPF of formulations prior to in vivo SPF tests in humans.25,26
Inclusion of OMC in liposomes increased the in vivo SPF values for the formulation. However, the SPF decreased after immersion, indicating that the liposome/OMC formulation had low water resistance. This is probably because the liposome/OMC is embedded in a totally aqueous gel formulation. The liposome itself did not provide the formulation with water resistance