The drug formulations providing prolonged releasing are preferred in the treatment of mental diseases. Biodegradable matrices based on copolymers of lactide and glycolide have been proposed for risperidone (RSP) targeting. They degrade releasing substance. In principle, drug release is usually controlled by diffusion, degradation or their combination. There are two widely used diffusion models for the explanation of diffusion-controlled release from matrices, i.e. Higuchi model and Korsmeyer-Peppas model. The aim of this study was to estimate the release rate of RSP from poly(L-lactide-co-glycolide) (L-PLGA) (85:15) matrices.
The matrices were obtained by solution casting method from L-PLGA (100000 Da) (85:15). Matrices (5 wt-% of RSP, with the diameter of 10 mm, thickness of 0.6273 mm ± 0.0196, n=3) were degraded in phosphate buffered saline (pH 7.4) at 37ºC under constant agitation.
The release rate was determined by high-performance liquid chromatography (VWR Hitachi, Merck). The theoretical profiles according to the Higuchi, Korsmeyer-Peppas equation were used. The data were processed by means of software package Excel 2013 and Visual basic 5.0.
RSP was released for 215 days and the cumulative amount was 2009.74 µg ± 24.49 (n=3). The fraction of initial release was 1.53 % ± 0.24. The loss of dry weight of matrices followed exponentially with a constant k = 0.0104 1/day. The total fraction of released RSP was the sum of initial release, relaxation-induced drug dissolution release and diffusion controlled release. The correlation coefficient of the Higuchi equation R2 = 0.89 ± 0.002 and the values of release exponent of the Korsmeyer-Peppas equation n > 0.89 indicate that drug release occurs by both swelling and erosion. The proposed models are adequate for the interpretation of RSP release form L-PLGA (85:15) matrices.
This work was financially supported by the National Centre for Research and Development, grant RYSPCONT no. PBS1/A7/2/201.

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