Drug release and adhesive properties of crospovidone-containing matrix patches based on polyisobutene and acrylic adhesives

Ethinyl estradiol and levonorgestrel were insoluble in blends of high:medium:low molecular weight polyisobutene adhesives (ratio: 1:5:0, 1:5:2 and 1:5:4) but soluble in acrylic adhesives (Durotak® 87-202A, Durotak® 87-2074 and Durotak® 87-2677). The incorporation of drug adsorbates onto crospovidone into the polyisobutene blends yielded crystal-free patches. The drug release from these patches was independent of polyisobutene's molecular weight distribution, probably because the drug release occurred mainly through fluid filled channels. By contrast, the drug release from acrylic adhesives was independent of whether the patches contained pure drugs or drug adsorbates onto crospovidone. A higher degree of saturation (or supersaturation) in these systems resulted in a higher thermodynamic activity of the drugs and hence a higher drug release. The crystal-free acrylic and polyisobutene patches did not show drug recrystallization after 3 months at 25 °C/60 RH and 40 °C/75 RH.The adhesive properties of polyisobutene patches were investigated in vitro and in vivo. The area under the curve of force–distance curves recorded with the texture analyzer correlated well with the in vivo skin adhesion. The elongation at detachment showed the same trend as the in vivo matrix creep. Crospovidone contents ≤30% had no detrimental effect on the adhesive properties of the patches.