THE PERCUTANEOUS ABSORPTION OF SALICYLATES 107 philic (oil-in-water). Figure 15 indicates no significant difference in the plasma levels produced with these bases. To compare all of the various types of vehicles a typical one from each group was selected and compared (Fig. 16). All of the curves are significantly different from one another. 'EFFECT OF THE SUBSTITUENT GROUP Volatile vehicles, usually ether were used when different derivatives ot Q OIL-•N-HaO U m / ,/ / • LIGHT ,' / '/ • LANOLIN I•/• .--•• GLYCOL MIX 15 3o I 2 (MIN) TIME (HOURS) Fig, 16.•Percutaneous absorption of 10• methyl salicylate in •arious type• of vehicles. 50 i i EMETHYL + E _-•N-BUTYL + E 5 THYL + E //•••--iso PROPYL+ E _ a. 40 ,,,• 50 ß J .•/ / •1 SO AMY L -I- E ! / • •.•'•.'-'AMYL + E 13:: U 20 ! // • ••BENZYL +E "'2 If! , .• •••'-GLYCO + E / o' !•?•, __= .. =_ I i _DiETHYLAMiNE.iH• j •, 0 , ' I 15 $0 I 2 $ H•O (MIN) .,-.M. ABS. ETHANOL TIME ( HOURS ) E ETHER Fig. 17.--Percutaneous absorption of different salicylate esters and salts in vola- tile vehicles.

108 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 18 •12 j• I I IO%METH. SAL IN ETHER • _ _ I -I / // •--N-BUTYL + E - -II / • /.---ISO AMYL E - II / • •-- •PHENYL + ••=-• I i•BENZYL + E o (M•N.) TIME (HOURS) Fig. 18.--Percutaneous absorption of different salicylate esters in ether (s:dicyl- ate ester as salicylic acid). salicylic acid were compared because these vehicles quickly evaporate eliminating any "vehicle effect." Comparisons of the percutaneous absorp- tion of different salicylate derivatives (in 10 per cent solutions) by the plas- ma, salicylic acid and ester salicylate levels are presented in Figs. 17 and 18, respectively. Ethyl and methyl salicylates produced the highest plasma salicylic acid levels (significant). Methyl salicylate is significantly better • I I I _• HYL SALICYL n 6 - tic 4 - - I • 0 •' , I i I I5 30 o (MIN.) I 2 3 TIME (HOURS) Fig. 19.--Percutaneous absorption of 10% ethyl salicylate and 10% ethyl aspirin in ether.