Table IA Composition of 2.0% Salicylic Acid Formulations Tested Reference Reference anionic nonionic Component formula formula Formula 1 Formula 2 Formula 3 Formula 4 Percentage of component Ethyl alcohol, 200 proof 42 * 42 42 42 42 Salicylic acid 2.0 2.0 2.0 2.0 2.0 2.0 Sodium lauryl sulfate 0.2 Isoceteth-20 * 0.9 0.9 0.9 0.9 Polyol prepolymer-15 1.0 2.0 3.0 Propylene glycol 0.8 Polyethylene glycol 0.8 EDTA tetrasodium salt (36%) * 0.05 0.05 0.05 0.05 T riethanolamine * 0.1 0.1 0.1 0.1 Glycerine 5.0 Citric acid 0.3 Water QS QS QS QS QS * Exact amount is unknown. Formula 5 Formula 6 Formula 7 42 42 42 2.0 2.0 2.0 0.9 3.0 3.0 0.05 0.05 0.05 0.1 0.1 QS QS QS Formula 8 42 2.0 0.2 3.0 0.8 0.8 5.0 0.3 QS ----..J 0 0 C z 0 n 0 C/'J tTJ - n C/'J n - z n tTJ
TARGETED DELIVERY OF SALICYLIC ACID Table 1B Composition of 0.5% Salicylic Acid Formulations Tested Component Ethyl alcohol, 200 proof Salicylic acid Disodium lauryl sulfosuccinate Isoceteth-20 Sodium lauroyl sarcosinate Polyolprepolymer-15 Polyethylene glycol-4 Sodium PCA (50%) EDTA tetrasodium salt (36%) T riethanolamine Glycerine Water Reference anionic formula Formula 9 Percentage of component 18 0.5 1.5 0.83 0.25 0.8 0.05 2.5 QS 31 0.5 0.9 0.05 0.1 QS 71 Formula 10 31 0.5 0.9 1.0 0.05 0.1 QS polymer slows the delivery of the drug through the skin in a dose-dependent fashion, even in hydroalcoholic surfactant systems. Figure 1 directly compares salicylic acid penetration through skin into the receptor at various time points from formulations with different surfactant systems, as mentioned. These are an anionic sodium lauryl sulfate hydroalcoholic system and the isoceteth-20 nonionic prototype hydroalcoholic formulations containing 0%, 2%, and 3% polyol­ prepolymer-15 (see Table IA). The anionic formulation exhibited the highest penetration rate of salicylic acid through the skin, significantly different (p 0.05) from all nonionic formulations at 24 hours (Table II, experiment two). This was followed by the isoceteth- 20 prototype formulation with no polymer, and the lowest penetration was for formu­ lation 4 with 3% polymer, which differed significantly from all others except formula­ tion 3 with 2% polymer (p 0.05 ). Clearly there is relatively more salicylic acid delivered to the receptor from the anionic formulation than from the nonionic formulations. Upon addition of the polymer, the drug is released more slowly into the receptor fluid over the 24-hour period, but clearly the drug is still penetrating through the skin for up to 24 hours (Figure 1). In fact there is a consistent increase in the amount of drug penetrating through the skin at each incubation time for all product treatments. The increase in drug in the receptor is slowest for the isoceteth-20 formulation containing the highest amount of polymer (the 3% polymer formula was significantly different at the p 0.05 level at 24 hours as compared to the anionic formula, the 0% polymer isoceteth-20 formula, and the commercial nonionic formulation, Table II). Thus the polymer effectively slows down delivery of the drug through the skin over the 24-hour period examined. Figure 2 replots the data in Figure 1 to examine only the additional drug that has penetrated into the receptor fluid rather than total drug accumulation at each measure­ ment time point during exposure of the skin to products. First of all, note that the maximum amount of drug that was delivered to the receptor occurred at the six-hour measurement for all formulations by 12 hours the additional drug delivered was con­ siderably diminished. Note that the highest maximum of salicylic acid penetration through the skin into the receptor occurred with the anionic sodium lauryl sulfate
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