GCL/GCP GELS ENHANCE SKIN DELIVERY OF MAP 281 solution, 1% GCP, 1% GC, and 1% GCL. In 10% ethanol vehicle, solution deposited more MAP into epidermis than the three polymer gels, while dermal deposition was comparable between 1% GCL and control solution, followed by 1% GC and 1% GCP. In addition, epidermal deposition of MAP was increased with GCL/GCP concentration in 10% ethanol. While the dermal deposition of MAP from 1% to 3% GCP showed similar trend, deposi- tion from 2% GCL appeared to be less than 1% and 3%. There was no signifi cant difference in epidermal deposition of MAP between the two polymers in either vehicle. Fatty acids have been widely used to improve transdermal delivery of both lipophilic and hydrophilic molecules (24). In general, saturated alkyl chain length of C10–C12 are more potent enhancers than the others, as a result of interacting and modifying the lipid do- main of the stratum corneum. However, when the fatty acids are grafted onto polymers such as GC, their penetration into the stratum corneum, and hence the interaction with lipids may be limited. Cerchiara et al. (12) have shown that the amphiphilic chitosan cross-linked with fatty acids increased hydrophilic drug solubility and hence skin pene- tration, and proposed polymer interaction with stratum corneum was the likely mecha- nism. The maximal effect was observed with the shorter cross-linker chain length. Our skin deposition data also showed strong concentration-dependent interaction of GCL/ GCP with the skin in comparison with GC, although we were not able to differentiate the effect between the two amphiphilic polymers. COMPARISON WITH CARBOPOL AND HPMC GELS MAP skin fl ux and skin deposition were also compared with the commercially available gels (Figure 5B and Table I). HPMC and 1% carbopol delivered only 14–28% skin fl ux of GCL/GCP gels at the same polymer concentration in 10% ethanol vehicle, and less Figure 3. MAP release rates from GC, GCL, and GCP gels in water and 10% ethanol vehicles. (***p 0.005)

JOURNAL OF COSMETIC SCIENCE 282 Figure 4. Skin permeation of MAP as a function of time from various polymer gels.