Masayuki Ishida

Effects of zonisamide on extracellular levels of monoamine and its metabolite, and on Ca2+ ependent dopamine release

The effects of zonisamide (3-sulfamoylmethyl-1,2-benzisoxazole), a novel anticonvulsant, on extracellular levels of monoamine and its metabolite in the striatum and hippocampus, and Ca2+ dependent monoamine release in the striatum of freely moving rats were studied by microdialysis. Zonisamide increased dopamine, homovanillic acid and 5-hydroxyindoleacetic acid, and decreased 3,4-dihydroxyphenylacetic acid in the rat striatum. However, zonisamide showed no effect on Ca2+ dependent dopamine release in the rat striatum. In the hippocampus, zonisamide increased dopamine, homovanillic acid, serotonin and 5-hydroxyindoleacetic acid and decreased 3,4-dihydroxyphenylacetic acid. The present results suggest that zonisamide facilitates dopaminergic and serotoninergic neurotransmission but does not affect Ca2+ dependent dopamine release within therapeutic plasma concentrations.

Associations Between Risk Factors for Valproate Hepatotoxicity and Altered Valproate Metabolism

Summary: The effects of three risk factors for valproate (VPA) hepatotoxicity (i.e., young age, polypharmacy, and high VPA serum level) on the metabolism of VPA to its monounsaturated metabolites 12‐en‐VPA (2‐en), 3‐en‐VPA (3‐en) and 4‐en‐VPA (4‐en)l were investigated in 106 patients treated with VPA (56 cases of monotherapy and 50 cases of polytherapy). In the monotherapy group, there was a significant negative correlation between age and 4‐en/VPA ratio. In the same group, the 4‐en/VPA ratio showed a significant positive correlation with serum VPA level, while 3‐enIVPA and 2‐enIVPA ratios showed significant negative correlations. In patients > 10 years, the 4‐enlVPA ratio was significantly higher, while the 2‐enIVPA ratio was significantly lower in the polytherapy group than in the monotherapy group. Our results indicate that all three risk factors clearly increase the metabolic conversion of VPA to 4‐en, the most toxic VPA metabolite, and that polytherapy and high VPA serum level result in the inhibited beta‐oxidative metabolism of VPA to 2‐en. These altered VPA metabolic profiles are strikingly similar to the abnormal VPA metabolism previously reported in cases with fatal hepatic failure. Although VPA‐induced fatal hepatotoxicity has been regarded as an idiosyncratic reaction, it is possible that these three factors enhance susceptibility to VPA hepatotoxicity by altering the metabolism of VPA.

The -141C Ins/Del polymorphism in the dopamine D2 receptor gene promoter region is associated with anxiolytic and antidepressive effects during treatment with dopamine antagonists in schizophrenic patients

Previous studies have demonstrated a lower density of dopamine D2 receptor (DRD2) in subjects without Del alleles of the -141C Ins/Del polymorphism in DRD2 gene promoter region than in those with one or two Del alleles. The present study aimed to examine whether the -141C Ins/Del DRD2 promoter polymorphism is related to therapeutic response to selective DRD2 antagonists in the treatment of schizophrenia. Subjects consisted of 49 acutely exacerbated schizophrenic inpatients treated with bromperidol (30 cases, mean dose +/- SD: 11.4 +/- 4.8 mg/day) or nemonapride (19 cases, 18 mg/day). Clinical symptoms were evaluated by the Brief Psychiatric Rating Scale (BPRS) before and 3 weeks after the treatment. The -141C Ins/Del DRD2 genotypes, the Ins and Del alleles, were determined by a polymerase chain reaction method. Thirty-five patients were homozygous for the Ins allele and 14 were heterozygous for the Del and Ins alleles. The patients without Del allele showed a higher percentage of improvement in anxiety-depression symptoms than those with Del allele (58.5 +/- 44.5% versus 24.1 +/- 48.2%) after 3 weeks of treatment while percentage improvement in total BPRS or other subgrouped symptoms (positive, negative, excitement and cognitive symptoms) was similar between the two genotype groups. The present results suggest that the -141C Ins/Del DRD2 polymorphism is associated with anxiolytic and antidepressive effects of neuroleptic treatment in schizophrenic patients.

Inhibition of trazodone metabolism by thioridazine in humans

To clarify the involvement of cytochrome P4502D6 (CYP2D6) in the metabolism of trazodone, the effects of coadministration of thioridazine, which is an inhibitor of this isozyme, on plasma concentrations of trazodone and its active metabolite m-chlorophenylpiperazine (m-CPP) were studied. The subjects were 11 depressed patients receiving trazodone at bedtime for 1–18 weeks. The dose was 150 mg in 10 patients and 300 mg in one. Thioridazine 40 mg/day was coadministered for 1 week, and blood samplings were performed before and after the coadministration. Thioridazine significantly (p < 0.001) increased plasma concentrations of both trazodone (713 ± 252 vs. 969 ± 370 ng/ml) and m-CPP (61 ± 22 vs. 94 ± 34 ng/ml). The present study thus suggests that CYP2D6 is involved in the metabolism of trazodone.

Effects of various CYP2D6 genotypes on the steady-state plasma concentrations of risperidone and its active metabolite, 9-hydroxyrisperidone, in Japanese patients with schizophrenia.

The effects of various CYP2D6 genotypes on the steady-state plasma concentrations (Css) of risperidone and its active metabolite, 9-hydroxyrisperidone, were studied in 85 Japanese schizophrenic patients (27 men and 58 women) treated with 6 mg/d risperidone for at least 2 weeks. Plasma concentrations of risperidone and 9-hydroxyrisperidone were measured using liquid chromatography–tandem mass spectrometry. The patients had the following CYP2D6 genotypes: wild-type (wt) /wt (40 patients), CYP2D6 * 10 (* 10)/ wt (28), CYP2D6 * 5 (* 5)/ wt (8), * 10/ * 10 (5), * 5/ * 10 (3), and CYP2D6 * 4/CYP2D6 * 14 (1), respectively. The Css values of risperidone and 9-hydroxyrisperidone were corrected to the median body weight of 58 kg. The medians (ranges) of the Css of risperidone in the aforementioned genotype groups were 2.2 (0.37–35.7), 6.4 (2.1–26.5), 12.3 (4.7–39.5), 19.4 (13.4–26.4), 64.0 (41.6–68.8), and 91.8 nmol/L. Those values for risperidone-to-9-hydroxyrisperidone ratio were 0.03 (0.01–0.33), 0.06 (0.03–0.19), 0.14 (0.07–0.29), 0.28 (0.25–0.38), 0.48 (0.38–0.58), and 2.35, respectively. The Css of risperidone was significantly (P < 0.05 or P < 0.001) different among the four genotype groups (wt/wt, * 10/wt, * 5/wt, and * 10/ * 10), except between the * 5/wt and * 10/ * 10 groups. Also, the risperidone-to-9-hydroxyrisperidone ratio significantly (P < 0.005 or P < 0.001) differed among these genotype groups. No significant differences were found in the Css of 9-hydroxyrisperidone and the active moiety (the Css of risperidone plus 9-hydroxyrisperidone) among these genotype groups. This study confirms previous findings that the CYP2D6 status affects the Css of risperidone via its strong regulation of 9-hydroxylation of risperidone. However, similar active moiety of risperidone among different genotype groups suggests that the determination of the CYP2D6 genotype has little importance for clinical situations.

Effects of various factors on steady state plasma concentrations of trazodone and its active metabolite m-chlorophenylpiperazine

Effects of various factors on steady state plasma concentrations of trazodone and its active metabolite m-chlorophenylpiperazine (mCPP) were studied in 43 depressed patients (19 males, 24 females) receiving trazodone 150 mg at bedtime for 1-3 weeks. Sixteen cases were smokers, and 19 cases were also receiving various benzodiazepines. The means (and ranges) of plasma concentrations of trazodone and mCPP, and the mCPP/trazodone ratio were 619 (251-1059) ng/ml, 59 (32-139) ng/ml and 0.100 (0.044-0.219), respectively. Smokers had significantly (p < 0.05) lower plasma concentrations of trazodone and higher mCPP/trazodone ratios than non-smokers. Age, sex and co-administration of benzodiazepines did not affect any plasma concentrations or the mCPP/trazodone ratio. In 11 cases where the dose was increased to 300 mg, neither plasma concentration/dose ratios nor the mCPP/trazodone ratio changed significantly. The present study thus suggests that: (1) there is a large Interindividual variation in the metabolism of trazodone; (2) smoking enhances the metabolism, but age, sex and co-administration of benzodiazepines do not affect it; (3) trazodone and mCPP have linear kinetics.

High‐performance Liquid Chromatographic Determination of Trazodone and 1‐m‐Chlorophenylpiperazine with Ultraviolet and Electrochemical Detector

A high‐performance liquid chromatographic (HPLC) assay was developed for the determination of trazodone and its metabolite, 1‐m‐chlorophenylpiperazine (m‐CPP), in plasma.

Effects of carbamazepine coadministration on plasma concentrations of trazodone and its active metabolite, m-chlorophenylpiperazine

Effects of carbamazepine coadministration on plasma concentrations of trazodone and its active metabolite, m-chlorophenylpiperazine (m-CPP) were studied in six depressed patients treated with trazodone. The daily dose of trazodone was 150 mg in three cases and 300 mg in three cases. Carbamazepine, 400 mg/day, was coadministered for 4 weeks, and blood samples were taken before carbamazepine addition and at weekly intervals after the addition. Carbamazepine significantly (p < 0.01) decreased plasma concentrations of not only trazodone but also m-CPP at each week. On the average, plasma concentrations of trazodone and m-CPP at 4 weeks were 24 and 40% of the corresponding precarbamazepine values. This study thus suggests that carbamazepine coadministration decreases plasma concentrations of trazodone and m-CPP by inducing the metabolism of these compounds.

Correlation between prolactin response and therapeutic effects of zotepine in schizophrenic patients.

The correlation between prolactin response and therapeutic effects of zotepine, as assessed by the Brief Psychiatric Rating Scale, was studied in 24 schizophrenic patients (12 males, 12 females), after 4 weeks of treatment. The daily dose was 100 mg in the first week, and 200 mg for the next 3 weeks. There were significant (p < 0.05) positive correlations between changes in serum prolactin concentration and amelioration scores of positive or total symptoms in males only. Thus, prolactin response may reflect therapeutic effects of zotepine, at least in males.

Is 2‐Propyl‐4‐Pentenoic Acid, a Hepatotoxic Metabolite of Valproate, Responsible for Valproate‐Induced Hyperammonemia?

Summary: To investigate the association between valproate metabolism (VPA) and VPA‐induced hyperammonemia together with the contribution of VPA hepatotoxicity risk factors such as young age, polypharmacy, and high serum VPA levels to VPA‐induced hyperammonemia, plasma ammonia (NH3) levels, serum levels of VPA and its metabolites, and biochemical parameters were determined in 98 patients treated with VPA (53 monopharmacy cases and 45 polypharmacy cases). In monopharmacy patients, plasma NH3 levels did not depend on age, VPA dosage or serum levels. Serum level of 2‐propyl‐4‐pentenoic acid (4‐en) showed a negative correlation with plasma NH3 level in the monopharmacy group. In polypharmacy patients, plasma NH3 levels, serum glutamic pyruvic transaminase, and γ‐glutamyltranspeptidase were significantly higher, while level/dose VPA ratio, 2‐en‐VPA serum level, and bilirubin were significantly lower than those in monopharmacy patients. These results suggest that young age and relatively high VPA serum levels within the therapeutic range were unlikely to be risk factors for common hyperammonemia associated with VPA therapy and that 4‐en was not causally related to this adverse effect. The decreased serum level of 2‐en‐VPA in polypharmacy patients may be a reflection of a certain mitochondrial dysfunction, which might be a mechanism of the increased NH3 levels. The changes in biochemical parameters in polypharmacy patients were considered results of the enzyme‐inducing activity of coadministered antiepileptic drugs (AEDs).