Enteric coating of nanostructured lipid carriers (NLCs) and enteric coating of hard gelatin capsules filled with NLCs: Feasibility studies

Nanostructured lipid carriers (NLCs) of asenapine maleate (ASPM) were enteric coated with polymethacrylate polymers (Eudragit®) for oral delivery. The present study aimed to compare the feasibility of direct enteric coating of NLCs and enteric coating of hard gelatin capsules filled with lyophilized ASPM-NLCs. Organic solution of Eudragit® was prepared using acetone containing 3% v/v water, acetone or ethanol. Aqueous dispersion of Eudragit® was obtained by neutralization with base. Capsules were enteric coated by dip-coating method with 3:2 ratio of Eudragit® L100-55:S100 (7.5-12.5% w/v). ASPM-NLCs showed particle size of 84.91±2.14nm, polydispersity index of 0.222±0.026, entrapment efficiency of 86.9±1.8% and zeta potential of -4.83±0.29 mV. TEM images showed good sphericity of the particles with the size of ≈100nm. Non-aqueous enteric coating was not successful as NLCs were precipitated in organic solvent. Aqueous enteric coated ASPM-NLCs (lipid:coat=1:2) showed an increased size (150.8±16.7nm) and zeta potential (-23.5±2.2 mV) revealing the deposition of Eudragit®. However, aqueous enteric coated ASPM-NLCs and uncoated ASPM-NLCs showed higher drug release (18.3±3.1-22.3±3.2%) in HCl solution (pH 1.2) indicating no resistance offered by direct enteric coating of NLCs; whereas enteric coated capsules showed less drug release (4.7±0.8%) in HCl solution indicating sufficient gastric protection.