The novel antipsychotic isoperidone, a prodrug of paliperidone, was designed to improve liposolubility for the development of poly(D,L-lactide-co-glycolide) (PLGA)-based microspheres to achieve near zero-order release behaviour in vivo. Microspheres with a smooth surface were obtained using the oil-in-water emulsion solvent evaporation method and yielded a high encapsulation efficiency of 92%. Pharmacokinetic studies in beagle dogs showed a one-week plateau phase followed by a two-week quasi-zero-order release with no burst release. The in vitro release method with a good in vitro-in vivo correlation was also established. Pharmacodynamic evaluation was performed using the MK-801-induced schizophrenic behavioural mouse model, and the sustained suppressive effect lasted two weeks. The pharmacokinetic-pharmacodynamic (PK-PD) relationship of isoperidone microspheres was compared to that of oral administration of free drug. The results revealed a strong correlation between the plasma drug level and the antipsychotic effect. A stable drug plasma concentration was detected in mice both intraday and interday from 8 to 22 d after a single injection of isoperidone microspheres, and a sustained suppressive effect on the schizophrenic model was also observed. In comparison, the mouse group receiving oral daily administration exhibited more dose-dependent effects, and the pharmacological effect diminished rapidly in conjunction with a reduction of the plasma drug levels 8h after the last administration of isoperidone on day 3. The above results confirm the superiority of long-acting release over oral administration and indicate a valuable alternative for the clinical treatment of schizophrenia.
Keywords: Antipsychotic; Microsphere; PK-PD relationship; Zero-order release.
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