Skin pre-treatment with propylene glycol (PG), PC or phosphatidylethanolamine (PE)
promoted drug permeation and shortened the lag time.
When repeating the same study on silastic membranes instead of skin,
none of the phospholipids accelerated drug permeation. Furthermore, PG, PE or PC did not significantly affect the percutaneous absorption of indomethacin through skin lacking
stratum corneum.
This clearly indicated that phospholipids act directly on the permeability barrier of SC