Acrylic acid–methyl methacrylate copolymer for oral prolonged drug release

Acrylic acid (AA)–methyl methacrylate (MMA) based copolymers, in different molar ratios (3:7, 4:6, 5:5, 6:4, and 7:3) were synthesized using tetrahydrofuran as solvent and AIBN as free radical initiator. Increase in acrylic acid concentration promoted pH-dependent swelling of copolymer and copolymer AA:MMA (3:7) was selected due to minimum swelling. ATR/FTIR and 1H NMR spectra of the copolymer showed absence of vinyl bond/protons present in the monomers suggesting successful polymerization. The copolymer was hemocompatible. Flurbiprofen sodium microspheres made with the copolymer, by oil/oil solvent evaporation, were spherical, anionic (zeta potential −59.0 mV) and contained 4.53% drug. ATR spectrum of microspheres showed peaks for aromatic C=C stretching and substituted benzene ring, indicating entrapment of flurbiprofen. XRD analysis revealed crystalline structure of flurbiprofen while copolymer and microspheres were amorphous. DSC thermograms showed a sharp melting endotherm of flurbiprofen sodium at 129.26°C against broad endotherms of copolymer and microspheres having peaks at 82.24 and 86.59°C, respectively. The thermogram of microspheres did not show the melting peak of flurbiprofen. The microspheres exhibited no drug release at pH <6.8 and released 83.4 and 99% drug at pH 6.8 and 7.4 in 3 h. The microspheres did not adhere on gastric mucosa at pH 1.2 but showed mucoadhesion time of 28 min on intestinal mucosa at pH 6.8. Thus, the microspheres on oral administration, would release the drug in distal ileum, suggesting the potential of the hemocompatible copolymer for enteric coating for prolonged drug release.