Stereospecific formulation and characterization of sustained release ibuprofen microspheres

Abstract

Ibuprofen microspheres were prepared from the racemate, (+)-S and (+)-R enantiomers using waxes such as ceresine and glyceryl stearate and stereo-specifically characterized. The method of preparation of the microspheres was a hydrophobic congeal able disperse phase encapsulation process and variables such as particle size, wax type, enantiomeric form were evaluated. Dissolution studies were carried out by a modified USP type II method and the samples were analysed by a stereospecific HPLC assay using S-(−)-1(1) naphthyl-ethylamine as the derivatizing agent and fenoprofen as the internal standard. The mean particle sizes of (+)-S and (−)-R enantiomers determined by microscopy/image analysis were 64 and 99 μm respectively while that of the racemate was 48 μm. Differential Scanning Calorimetry (DSC) of ibuprofen and the enantiomers showed endothermic peaks at 72 and 55°C respectively. Thermograms of the physical mixture and microspheres did not show the characteristic ibuprofen peak, indicating a change in crystallinity of the drug. Powder X-ray diffraction patterns of the enantiomers and racemic ibuprofen were found to be dissimilar indicating different crystal properties. The X-ray patterns for the microspheres did not show the characteristic peaks for the drug indicating that ibuprofen may be in solid solution with the waxes. Scanning electron micrographs of the microspheres showed a generally smooth and spongy appearance for the microspheres made of compritol and glyceryl stearate. Microspheres made from the paraffin waxes had rough and hard surface characteristics consistent with the higher melting point of the waxes. Ceresine microspheres made with the enantiomers had a rougher and more porous surface compared to the microspheres made with racemic ibuprofen. Stereospecific release of the racemate from the formulations was found to be sustained (T₂₅ of 4 h), while release from the enantiomers was less sustained (T₅₀ of 2 h). From the S:R ratios and statistical analysis of the data, the release of the enantiomers of ibuprofen from the formulations containing the racemate was found to be non-stereoselective.

Key Words:

• Ibuprofen
• microsphere
• sustained release
• stereospecific