High-performance liquid chromatographic determination of cis-N-(1-benzyl-2-methylpyrrolidin-3-yl)-5-chloro-2-methoxy-4- methylaminobenzamide in rat blood and brain using electrochemical detection

Biotransformation of post-clozapine antipsychotics: pharmacological implications

The need to develop new antipsychotics that have fewer motor adverse effects and offer better treatment of negative symptoms has led to a new generation of drugs. Most of these drugs undergo extensive first-pass metabolism and are cleared almost exclusively by metabolism, except for amisulpride whose clearance is largely due to urinary excretion. Risperidone has metabolic routes in common with ziprasidone but shows differences in regard to other main pathways: the benzisoxazole moiety of risperidone is oxidised by cytochrome P450 (CYP) 2D6 to the active 9-hydroxyrisperidone, whereas the benzisothiazole of ziprasidone is primarily oxidised by CYP3A4, yielding sulfoxide and sulfone derivatives with low affinity for target receptors in vitro. Olanzapine, quetiapine and zotepine also have some common metabolic features. However, for the thienobenzodiazepine olanzapine a main metabolic route is direct conjugation at the benzodiazepine nucleus, whereas for the dibenzothiazepine quetiapine and the dibenzothiepine zotepine it is CYP3A4-mediated oxidation, leading to sulfoxidation, hydroxylation and dealkylation for quetiapine, but N-demethylation to the active nor-derivative for zotepine. Although the promising benzisoxazole (iloperidone) and benzisothiazole (perospirone) antipsychotics share some metabolic routes with the structurally related available drugs, they too have pharmacologically relevant compound-specific pathways. For some of the new antipsychotics we know the isoenzymes involved in their main metabolic pathways and the endogenous and exogenous factors that, by affecting enzyme activity, can potentially modify steady-state concentrations of the parent drug or its metabolite(s), but we know very little about others (e.g. amisulpride isomers, nemonapride). For yet others, information is scarce about the activity of the main metabolites and whether and how these contribute to the effect of the parent drug. Aging reduces the clearance of most antipsychotics, except amisulpride (which requires further evaluation) and ziprasidone. Liver impairment has little or no effect on the pharmacokinetics of olanzapine, quetiapine, risperidone (and 9-hydroxy-risperidone) and ziprasidone, but information is lacking for amisulpride. Renal impairment significantly reduces the clearance and prolongs the elimination half-life of amisulpride and risperidone. Again, studies are still not available for some drugs (zotepine) and have focused on the parent drug for others (olanzapine, quetiapine, ziprasidone) despite the fact that renal impairment would be expected to lower the clearance of more polar metabolites. Addressing these issues may assist clinicians in the design of safe and effective regimens for this group of drugs, and in selecting the best agent for each specific population.

High-performance liquid chromatographic determination of nemonapride and desmethylnemonapride in human plasma using an electrochemical detection

A high-performance liquid chromatographic method using an electrochemical detector (HPLC-ED) was developed for the determination of nemonapride and its active metabolite, desmethylnemonapride in human plasma. Nemonapride, desmethylnemonapride and moperone chloride, which was used as the internal standard (I.S.) in plasma, were extracted by a rapid and simple procedure based on C18 bonded-phase extraction, and were separated by C8 reversed-phase HPLC column. Nemonapride and desmethylnemonapride were detected by high conversion efficiency amperometric detection at +0.84 V. Determination of both nemonapride and desmethylnemonapride were possible in the concentration range at 0.25-5.0 ng/ml, and the limit of detection for each was 0.1 ng/ml. The recoveries of nemonapride and desmethylnemonapride added to plasma were 97.0-98.2% and 96.7-98.8%, respectively, with coefficients of variation of less than 7.2% and 10.3%, respectively. This method is applicable to drug level monitoring in the plasma of schizophrenia patients treated with nemonapride and to the study of pharmacokinetics.