Absorption, metabolism, and excretion of paliperidone, a new monoaminergic antagonist, in humans.

Absorption, metabolism, and excretion of paliperidone, an atypical antipsychotic, was studied in five healthy male subjects after a single dose of 1 mg of [(14)C]paliperidone oral solution ( approximately 16 microCi/subject). One week after dosing, 88.4 to 93.8% (mean 91.1%) of the administered radioactivity was excreted: 77.1 to 87.1% (mean 79.6%) in urine and 6.8 to 14.4% (mean 11.4%) in the feces. Paliperidone was the major circulating compound (97% of the area under the plasma concentration-time curve at 24 h). No metabolites could be detected in plasma. Renal excretion was the major route of elimination with 59% of the dose excreted unchanged in urine. About half of the renal excretion occurred by active secretion. Unchanged drug was not detected in feces. Four metabolic pathways were identified as being involved in the elimination of paliperidone, each of which accounted for up to a maximum of 6.5% of the biotransformation of the total dose. Biotransformation of the drug occurred through oxidative N-dealkylation (formation of the acid metabolite M1), monohydroxylation of the alicyclic ring (M9), alcohol dehydrogenation (formation of the ketone metabolite M12), and benzisoxazole scission (formation of M11), the latter in combination with glucuronidation (M16) or alicyclic hydroxylation (M10). Unchanged drug, M1, M9, M12, and M16 were detected in urine; M10 and M11 were detected in feces. The monohydroxylated metabolite M9 was solely present in urine samples of extensive CYP2D6 metabolizers, whereas M10, another metabolite monohydroxylated at the alicyclic ring system, was present in feces of poor metabolizers as well. In conclusion, paliperidone is not metabolized extensively and is primarily renally excreted.

Maintenance therapy with once-monthly administration of long-acting injectable risperidone in patients with schizophrenia or schizoaffective disorder: a pilot study of an extended dosing interval.

BACKGROUND: Several clinical studies have established the efficacy, safety, and tolerability of long-acting risperidone administered once every 2 weeks in patients with schizophrenia or schizoaffective disorder. This report evaluates preliminary efficacy, safety, tolerability, and pharmacokinetic data for a novel (once-monthly) administration of long-acting injectable risperidone 50 mg in patients with schizophrenia or schizoaffective disorder. METHODS: Clinically stable patients participated in a 1-year, open-label, single-arm, multicenter pilot study. During the 4-week lead-in phase, patients received long-acting risperidone 50 mg injections every 2 weeks, with 2 weeks of oral risperidone supplementation. Injections of long-acting risperidone 50 mg every 4 weeks followed for up to 48 weeks, without oral supplementation. The primary endpoint was relapse; other assessments included PANSS, CGI-S, adverse event reports, and determination of risperidone and 9-hydroxyrisperidone plasma concentrations. RESULTS: Twelve patients in the intent-to-treat population (n = 67) met relapse criteria (17.9%). Relapse risk at 1 year was estimated as 22.4%. Non-statistically significant improvements in symptoms (PANSS) and clinical status (CGI-S) at endpoint were observed. The most common adverse events included schizophrenia aggravated not otherwise specified (19.5%), anxiety (16.1%), insomnia (16.1%), and headache (11.5%). There were no unexpected safety and tolerability findings. Mean plasma concentrations for risperidone and 9-hydroxyrisperidone were generally stable during the study. CONCLUSION: Once-monthly dosing of long-acting risperidone was well tolerated, associated with a relatively low relapse rate (similar to that reported with other antipsychotics), and maintained the clinically stable baseline status of most patients. Although the results suggest that some symptomatically stable patients with schizophrenia or schizoaffective disorder might be safely managed with long-acting risperidone 50 mg once monthly, these findings alone do not identify which patients will have a sufficient therapeutic benefit nor do they quantify comparative effects of standard and altered dosing. Study limitations (the open-label pilot study design, small sample size, and lack of a concurrent biweekly treatment arm) prevent broad interpretations and extrapolations of results. Controlled studies would be required to support a recommendation for alternative dosing regimens.