Impact of degree of substitution of acetylated Ofada rice starch polymer on the release properties of nimesulide microspheres .

ABSTRACT

Nimesulide microspheres were prepared by the quasi-emulsion solvent diffusion method, using acetylated

starches of the indigenous Ofada rice (Oryza glaberrima Steud) with degrees of substitution (DS) 1.42 and 2.62.

A full 23 factorial experimental design was performed using DS (X1), drug:polymer ratio (X2) and polymer

concentration (X3) as independent factors; size, entrapment, swelling and time taken for 80% drug release (t80)

were the dependent variables. Contour plots were generated and data from the in vitro release studies were

fitted to various kinetic models. Nimesulide microspheres were near-spherical, sizes varying from

50.91±16.22 to 74.24±24.73 μm for microspheres containing starch DS 1.42 and from 21.05±4.25 to

46.10±3.85 μm for starch DS 2.62. Drug entrapment was 56.75±0.45 to 98.28±2.30%. DS had the greatest

effect on the size, swelling and dissolution time (p = 0.01) which was confirmed by the contour plots. The

interaction between factors DS and drug:polymer ratio (X1X2) had the greatest effect on the microsphere

properties (p = 0.04). Drug release was fitted into the First Order, Higuchi and Korsmeyer models. Acetylated

starch of Ofada rice DS 2.62 was found more suitable for the formulation of microspheres because of

reduced size and swelling, higher entrapment and prolonged drug release.

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