Bacterial degradation of risperidone and paliperidone in decomposing blood

The stability of two benzisoxazole antipsychotics was determined in vitro in decomposing porcine blood inoculated with bacteria, utilizing a high-performance liquid chromatography with ultraviolet and fluorescence detection method for drug quantitation. Stability experiments for risperidone and paliperidone were conducted at 7, 20 and 37°C for 4 days using sterile and bacterially inoculated porcine blood. The drugs were stable in sterile blood at each temperature and in inoculated blood at 7°C, but degraded significantly in inoculated blood at 20 and 37°C. Complete loss occurred within 2 days when incubated at 37°C. The benzisoxazole-cleaved degradation products for both drugs were identified as 2-hydroxybenzoyl-risperidone and 2-hydroxybenzoyl-paliperidone utilizing liquid chromatography quadrupole-time-of-flight mass spectrometry and accurate mass measurements. The degradation products have been found in postmortem case studies, including one case where risperidone and paliperidone were not detected, indicating complete conversion can occur in situ.