Elucidating Molecular State of Loxoprofen in Acrylic Adhesive Patches Which Could Relate Transdermal Drug Permeability

The purpose of this study was to investigate the effect of the interaction between hydrophilic drugs and acrylic polymers in the adhesive layer of matrix-type patches on skin permeability. Loxoprofen is a nonsteroidal anti-inflammatory drug which has poor permeability. To improve that, patches were prepared using loxoprofen sodium hydrate (LP-Na) as the active pharmaceutical ingredient and acrylic polymers with four different functional groups with different molecular weights. In addition, to enhance the permeability of the patches, we add the lactic acid (LA) as an additive. The crystalline state of the patches was examined by polarizing microscopy and powder X-ray diffraction. The interaction between LP-Na and acrylic polymers was also evaluated using ¹H-NMR. The drug release rate and in vitro skin permeation from the patches were evaluated by dissolution apparatus (paddle method) and Franz diffusion cell, respectively. In patches using acrylic polymers with carboxy groups (AO), the skin permeation test suggested that the LP-Na_AO patch system showed 2.5 times better permeability compared with other patches. Interestingly, addition of LA (LP-Na_AO + LA) also improved 1.5 times more diffusion rate than LP-Na_AO patch and other systems. The interaction of LP-Na with acrylic polymers and LA as pH modifier would enhance the permeability of LP from matrix-type adhesive patches.