Relationship between the plasma concentration of paliperidone and the clinical and drug‐induced extrapyramidal symptoms in elderly patients with schizophrenia

OBJECTIVE: We investigated the relationship between the plasma concentration of paliperidone (PAL) and clinical and drug-induced extrapyramidal symptoms (EPS) in elderly patients with schizophrenia. METHODS: In this study, 15 patients with schizophrenia receiving risperidone were switched to PAL and treated for 12 weeks. Their clinical symptoms were assessed using the Positive and Negative Syndrome Scale and the Clinical Global Impression-Severity of Illness Scale. Their EPS were assessed using the Drug-induced EPS Scale, Abnormal Involuntary Movement Scale, and Barnes Akathisia Scale at baseline and 12 weeks. Plasma concentrations were measured by the liquid chromatography-mass spectrometry/mass spectrometry method. RESULTS: The results revealed that there were significant correlations between the plasma concentration of PAL and improved Positive and Negative Syndrome Scale total, negative, and general psychopathology scores (p<0.05). However, the efficacy did not improve linearly with plasma level. No significant correlations were found between the PAL plasma concentration and the mean change from baseline in the Drug-induced EPS Scale total score, Barnes Akathisia Scale, or Abnormal Involuntary Movement Scale. CONCLUSIONS: The results of this research suggested that, in elderly patients, although none of an increased plasma concentration of PAL, a worsening of EPS, or an increase in prolactin level occurs, linear clinical efficacy may not be obtained.