Only one medical product with a prolonged release of risperidone (RSP) is available at present, i.e. a long-acting injection including encapsulated microspheres of poly(D,L-lactide-co-glycolide) (D,L-PLGA) (75:25). The administration of aqueous suspension may be painful and microspheres cannot be removed upon complications. The aim of this study was to develop an alternative solutions based on implantable formulation composed of D,L-PLGA (70:30).
Matrices containing 10 wt-% (n =10, 10 mm) were prepared by solution casting method from D,L-PLGA (70:30) (460000 Da). They were incubated in phosphate buffered saline (pH 7.4) at 37ºC under constant agitation.
The tests performed included: determination of RSP concentration by high-performance liquid chromatography (VWR Hitachi, Merck); composition and chain structure by nuclear magnetic resonance spectroscopy (AVANCE II Ultra Shield Plus Bruker 600 MHz spectrometer); thermal properties by means of differential scanning calorimetry (TA DSC 2010 apparatus, New Castle, DE); morphological study by a scanning electron microscope (Quanta 250, FEI Quanta FEG) and atomic force microscopy using MultiMode 3 (di-Veeco, CA).
RSP was detected within the period of 51 days. The cumulative amount was 4498 mg ± 682 (n= 10). The loss of dry weight followed exponentially with a constant k = 0.047 1/day. The incubation led to the decrease of the amount of glycolidyl units and increase in the amount of lactidyl units; the reduction of the average length of glycolidyl and lactidyl blocks; the decrease of glass transition temperature. The copolymer became more random. The morphological study shows a greater morphological differentiation of the incubated samples. The properties of D,L-PLGA (70:30) matrices afford the possibility of obtaining an implantable drug formulation for a prolonged release of RSP.
This work was financially supportedby the National Centre for Research and Development, grant RYSPCONT no. PBS1/A7/2/201.

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