THE PERCUTANEOUS ABSORPTION OF SALICYLATES 105 a_ 60 •=•PETROLATUM - ,,,'• I ••LIGHT n-• / f f __---- -- M I N K OIL - m,m• 40 m-- • • • /ALMOND OIL I /-• J • •jCOD LIVER OIL •, •'"'LARD • 20 t- ,' .-'••••• --cRisco - i / ' •,• • 0 I/'"' I I I TIME (HOURS} Fig. 12.--?ercutaneous absorption of 10% methyl salicylate in different vehicles. • 80 I I • = c U') A- TRILAURYL {TETRAGLYCOL ETHER) PHOSPHATE ,• A m B - Na LAURYL {TETRAGLYCOL ETHER) SULFATE • a. C-DiLAURYL {TETRAGLYCOL ETHER) • 60 - -- - SUEFATE .•"• • D- TRILAURYL PHOSPHATEJJ • 4o - - o // B ' 20 - / /• ' I 2 • TIME (HOURS} Fig. 13.--Percutaneous absorption of 10% methyl salicylate in alkyl phosphates and alkyl sulfates. vehicles for methyl salicylate. The results obtained with alkyl phosphates and alkyl sulfates as bases are shown in Fig. 13. Trilauryltetraglycol- ether phosphate produced significantly higher salicylate levels than all the other compounds in this group at one hour. Di-lauryl tetraglycolether sulfate xvas significantly superior to the others after one hour. However, this compound produced petechiae in the skin so that the increase in ab- sorption may have been due to damage to the skin barrier.

106 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The results obtained •vhen alcohols were used for vehicles are shown in Fig. 14. Ethyl alcohol gave significantly higher blood levels than propylene glycol. Adding 35 per cent glycerol had no significant effect. To test the relative efficiency of water-in-oil rs. oil-in-water emulsions, our Develop- ment Laboratory at Bristol-Mye. rs prepared two emulsions, which contained. 60 per cent H20 and were identical in every detail except for the emulsifier which in one case was hydrophobic (water-in-oil) and in the other hydro- IlO 90 70 J 5O =t, 3o I•ABS. ETHANOL i i - •5%ABS. ETHANOL - / • •5%GLYCER- i i - I t / PROPYLENE I t • GLYCOL -- t -- I // i I 2 TIME (HOURS) Fig. 14.--Percutaneous absorption of 10% methyl salicylate in various alcohols. IO0 80 - 60 - 40 - 20 - o // 0 o WATER-IN-OIL - / ! l/! TIME (HOURS) Fig. 15.--Percutaneous absorption of 10% methyl salicylate in oil-in-water and water-in-oil vehicles.