Drug release and surface morphology studies on salbutamol controlled release pellets

The air suspension technique was employed to prepare controlled release pellets of Salbutamol (as the sulphate). The aim of the present study was to determine the influence of various film coating additives on the release characteristics and surface morphology features of salbutamol sulphate pellets coated with EudragitR RS30D which is the aqueous dispersion of a polymer synthesised from acrylic and methacrylic acid esters. Surface morphology features, which were examined using Scanning Electron Microscopy, revealed that triethyl citrate (plasticiser) was essential for the coalescence of polymeric membranes around the drug-loaded spheres. Higher concentrations (12.5% of triethyl citrate displayed a more uniform and continuous polymer film resulting in a slower in vitro drug release. Micrographs of the cross-sections of pellets with higher concentrations of EudragitR RS30D indicated the formation of thicker polymer membranes which accounted for the slower drug release rates. Hydroxypropyl methylcellulose (HPMC) inclusion in the polymer film coating increased salbutamol release rates due to its hydrophilic nature which promoted the formation of pores and cracks on the polymer films. A slower in vitro release of salbutamol was observed with higher concentrations of the hydrophobic anti-tackiness agent, magnesium stearate. The addition of salbutamol sulphate powder to the polymer dispersion enhanced drug release rates due to increased film permeability. Polyethylene glycol 200 (PEG 200) resulted in an increased in vitro drug release due to both its water soluble nature as well as impairment of film formation attributed to too high a plasticiser content in the coating formulation. As compared to polyethylene glycol 300 (PEG 300) as a plasticiser, triethyl citrate retarded drug release to a greater extent and formed more homogeneous and compact polymer films. The moisture content of PEG 300 plasticised pellets showed a 0.6% increase in moisture content while triethyl citrate plasticised pellets displayed a loss of 0.01% moisture 8 weeks after storage at room temperature. © 1995 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.