Risperidone (RSP) as a medical product is available in the formulation of a long-acting injection administrated as aqueous suspension of encapsulated microspheres of poly(D,L-lactide-co-glycolide). Currently offered alternative solutions, i.e. nano-, microparticles or implants, include copolymers of lactide and glycolide with various composition and chain structure. An alternative formulation has been developed. Decisive in RSP release is the rate of copolymer degradation. Determination of degradation changes in copolymer e.g. thermal and morphological properties seem to be helpful for analysis of drug release. The aim of this study is to determine thermal and morphological properties in the course of degradation process.
The matrices were obtained from poly(L-lactide-co-glycolide) (L-PLGA) (85:15) (100000 Da) by solution casting method. Matrices containing 5 wt-% of RSP were incubated in phosphate buffered saline (pH 7.4) at 37ºC under constant agitation for 0, 7, 14, 48, 58 and 105 days. Subject to performance were the tests of thermal characteristics by differential scanning calorimetry (DSC) using the TA DSC 2010 apparatus (TA Instruments, New Castle, DE); the morphological study by a scanning electron microscope (Quanta 250, FEI Quanta FEG).
The thermal analysis revealed the gradual decrease of glass transition temperature during observation period. Morphological study revealed that non-degraded matrix possessed a solid structure with single pores. The degradation influenced porosity significantly, also the widening of pores’ diameter and their deformation.
The performed thermal and morphological analyses of L-PLGA (85:15) matrices reveal their suitability in the interpretation of degradation processes. Matrices show that gradual degradation makes prolonged release of RSP possible.
This work was financially supported by the National Centre for Research and Development, grant RYSPCONT no. PBS1/A7/2/201.

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