Evidence for solanidine as a dietary CYP2D6 biomarker: Significant correlation with risperidone metabolism

AIMS

The extensive variability in cytochrome P450 2D6 (CYP2D6) metabolism is mainly caused by genetic polymorphisms. However, there is large, unexplained variability in CYP2D6 metabolism within CYP2D6 genotype subgroups. Solanidine, a dietary compound found in potatoes, is a promising phenotype biomarker predicting individual CYP2D6 metabolism. The aim of this study was to investigate the correlation between solanidine metabolism and the CYP2D6-mediated metabolism of risperidone in patients with known CYP2D6 genotypes.

METHODS

The study included therapeutic drug monitoring (TDM) data from CYP2D6-genotyped patients treated with risperidone. Risperidone and 9-hydroxyrisperidone levels were determined during TDM, and reprocessing of the respective TDM full-scan high-resolution mass spectrometry files was applied for semi-quantitative measurements of solanidine and five metabolites (M402, M414, M416, M440 and M444). Spearman's tests determined the correlations between solanidine metabolic ratios (MRs) and the 9-hydroxyrisperidone-to-risperidone ratio.

RESULTS

A total of 229 patients were included. Highly significant, positive correlationswere observed between all solanidine MRs and the 9-hydroxyrisperidone-to-risperidone ratio (ρ > 0.6, P < .0001). The strongest correlation was observed for the M444-to-solanidine MR in patients with functional CYP2D6 metabolism, i.e., genotype activity scores of 1 and 1.5 (ρ 0.72-0.77, P < .0001).

CONCLUSION

The present study shows strong, positive correlations between solanidine metabolism and CYP2D6-mediated risperidone metabolism. The strong correlation within patients carrying CYP2D6 genotypes encoding functional CYP2D6 metabolism suggests that solanidine metabolism may predict individual CYP2D6 metabolism, and hence potentially improve personalized dosing of drugs metabolized by CYP2D6.

Involvement of the TNF-α/SATB2 axis in the induced apoptosis and inhibited autophagy of osteoblasts by the antipsychotic Risperidone

BACKGROUND

Risperidone, an atypical antipsychotic, impedes serotonin and dopamine receptor systems. Meanwhile, tumor necrosis factor-α (TNF-α) is known to participate in regulating osteoblast functions. Consequently, the current study aimed to investigate whether the influences of Risperidone on osteoblast functions are associated with TNF-α and special AT-rich sequence-binding protein (SATB2).

METHODS

Firstly, we searched the DGIdb, MEM and GeneCards databases to identify the critical factors involved in the effects of Risperidone on osteoblasts, as well as their interactions. Afterwards, osteoblast cell line MC3T3-E1 was transduced with lentivirus carrying si-TNF-α, si-SATB2 or both and subsequently treated with Risperidone. Various abilities including differentiation, autophagy and apoptosis of osteoblasts were examined after different treatments. Finally, animal experiments were performed with Risperidone alone or together with lentivirus to verify the function of Risperidone in vivo and the mechanism.

RESULTS

It was found that Risperidone might promote TNF-α expression, thereby inhibiting the expression of SATB2 to affect the autophagy and apoptosis in osteoblasts. Furthermore, as shown by our experimental findings, Risperidone treatment inhibited the differentiation and autophagy, and promoted the apoptosis of osteoblasts, as evidenced by elevated levels of OPG, p62, cleaved PARP1, cleaved caspase-3, cleaved caspase-8, and cleaved caspase-9, and reduced levels of LC3 II/I, Beclin1, collagen I, and RANKL. In addition, Risperidone was also found to elevate the expression of TNF-α to down-regulate SATB2, thereby inhibiting the differentiation and autophagy and enhancing the apoptosis of osteoblasts in vitro and in vivo.

CONCLUSIONS

Collectively, our findings indicated that Risperidone affects the differentiation of osteoblasts by inhibiting autophagy and enhancing apoptosis via TNF-α-mediated down-regulation of SATB2.

Distinct inactive conformations of the dopamine D2 and D3 receptors correspond to different extents of inverse agonism

By analyzing and simulating inactive conformations of the highly homologous dopamine D2 and D3 receptors (D2R and D3R), we find that eticlopride binds D2R in a pose very similar to that in the D3R/eticlopride structure but incompatible with the D2R/risperidone structure. In addition, risperidone occupies a sub-pocket near the Na+ binding site, whereas eticlopride does not. Based on these findings and our experimental results, we propose that the divergent receptor conformations stabilized by Na+-sensitive eticlopride and Na+-insensitive risperidone correspond to different degrees of inverse agonism. Moreover, our simulations reveal that the extracellular loops are highly dynamic, with spontaneous transitions of extracellular loop 2 from the helical conformation in the D2R/risperidone structure to an extended conformation similar to that in the D3R/eticlopride structure. Our results reveal previously unappreciated diversity and dynamics in the inactive conformations of D2R. These findings are critical for rational drug discovery, as limiting a virtual screen to a single conformation will miss relevant ligands.

Delivery of risperidone from gels across porcine skin in vitro and in vivo in rabbits

The purpose of this study was to develop and evaluate a transdermal delivery system for RIS using hydrogels. First, the effects of different concentrations of hydroxypropyl methylcellulose and Carbomer 934 (CBR) on RIS permeation were investigated in porcine skin. The optimized formulation was chosen as the base gel to screen for penetration enhancers. The pharmacokinetics of the optimized RIS formulation was then studied in vitro in rabbits. A formulation with 0.5% CBR showed the highest RIS permeation and was selected as the base gel. RIS permeation was further increased by incorporation of Azone, lauryl alcohol, or menthol, and the enhancing effects of the three were dose-dependent. When each enhancer combined with propylene glycol (PG) a synergistic effect was found. A combination of 6% menthol and 6% PG exhibited highest RIS in vitro penetration rate and showed a high efficiency in vivo, with a relative bioavailability of 131.53% compared with intragastric administration. These findings showed that 1% RIS in 0.5% CBR, containing a combination of 6% menthol and 6% PG, can deliver doses of RIS that are therapeutically relevant for treating patients with schizophrenia.

Frontal D2/3 Receptor Availability in Schizophrenia Patients Before and After Their First Antipsychotic Treatment: Relation to Cognitive Functions and Psychopathology

BACKGROUND

We have previously reported associations between frontal D2/3 receptor binding potential positive symptoms and cognitive deficits in antipsychotic-naïve schizophrenia patients. Here, we examined the effect of dopamine D2/3 receptor blockade on cognition. Additionally, we explored the relation between frontal D2/3 receptor availability and treatment effect on positive symptoms.

METHODS

Twenty-five antipsychotic-naïve first-episode schizophrenia patients were examined with the Positive and Negative Syndrome Scale, tested with the cognitive test battery Cambridge Neuropsychological Test Automated Battery, scanned with single-photon emission computerized tomography using the dopamine D2/3 receptor ligand [(123)I]epidepride, and scanned with MRI. After 3 months of treatment with either risperidone (n=13) or zuclopenthixol (n=9), 22 patients were reexamined.

RESULTS

Blockade of extrastriatal dopamine D2/3 receptors was correlated with decreased attentional focus (r = -0.615, P=.003) and planning time (r = -0.436, P=.048). Moreover, baseline frontal dopamine D2/3 binding potential and positive symptom reduction correlated positively (D2/3 receptor binding potential left frontal cortex rho = 0.56, P=.003; D2/3 receptor binding potential right frontal cortex rho = 0.48, P=.016).

CONCLUSIONS

Our data support the hypothesis of a negative influence of D2/3 receptor blockade on specific cognitive functions in schizophrenia. This is highly clinically relevant given the well-established association between severity of cognitive disturbances and a poor functional outcome in schizophrenia. Additionally, the findings support associations between frontal D2/3 receptor binding potential at baseline and the effect of antipsychotic treatment on positive symptoms.

Risperidone for bipolar disorders

Atypical antipsychotic medications are a relatively new, increasingly prominent component of the treatment armamentarium for bipolar disorder -- a development that provides more options for potentially improved outcomes for patients and families affected by bipolar disorder. The US Food and Drug Administration-approved bipolar indications for risperidone include monotherapy for the short-term treatment of acute manic or mixed episodes associated with bipolar I disorder and combination therapy with lithium or valproate for the short-term treatment of acute manic or mixed episodes associated with bipolar I disorder. Risperidone is also approved in over 30 countries worldwide for bipolar mania either as monotherapy, adjunct therapy, or both monotherapy and adjunct therapy. A number of controlled and open-label treatment trials have shown risperidone's efficacy and tolerability in the manic phase of bipolar disorder. Risperidone has also been reported to be useful in the longer-term treatment of bipolar disorder. This drug profile of risperidone for bipolar disorder will address the chemistry, pharmacodynamics, pharmacokinetics and metabolism of risperidone, clinical trials in bipolar disorder, postmarketing surveillance, safety, tolerability and regulatory issues. Finally, a discussion of potential future directions, a summary of key issues and information resources are provided.

Assessment of adverse effects of neurotropic drugs in monkeys with the "drug effects on the nervous system" (DENS) scale

Research into therapeutics for neuropsychiatric disorders is increasingly focusing on drugs with new mechanisms of action, and such agents are often assessed in preclinical studies using nonhuman primates. However, researchers lack a standardised method to compare different drugs for common adverse effects on the nervous system. We have developed a new scale for this purpose, named "Drug Effects on the Nervous System" (DENS), and tested its utility in an analysis of the second-generation antipsychotic risperidone in monkeys. The behavioural effects of risperidone over a ten-fold clinically relevant exposure range were rated with the DENS scale and compared with a standard motor disability scale for primates. The ratings were correlated with projected D2 and 5-HT2A receptor occupancies over time. The DENS scale detected dose-dependent side effects of risperidone in addition to the motor effects detected with the motor disability scale, including cognitive, sensorimotor and autonomic functions. A consistent temporal association between the DENS scale changes and the projected D2 receptor occupancy was observed, and the DENS scale ratings demonstrated high inter-rater reliability. These results demonstrate the usefulness of the DENS scale as a highly sensitive, reliable and accurate method to identify common adverse effects of risperidone and potentially other neurotropics for translational studies in primates.

Risperidone interacts with serum albumin forming complex

The aim of the work is to study the mechanisms of the interaction of risperidone with human and bovine serum albumins using the fluorescence quenching technique. Risperidone is an atypical antipsychotic drug used to treat many psychiatric disorders. We selectively excited the fluorescence of tryptophan residues with a 290 nm wavelength light, and observed quenching by titrating human and bovine serum albumin solutions with risperidone. Emission spectra were recorded in the range from 300 to 450 nm for each quencher addition. Stern-Volmer graphs were plotted and quenching constants were estimated. Results showed that the drug quenches the fluorescence of the human serum albumin by the formation of a complex risperidone-albumin. Association constants calculated from Stern-Volmer equation for low concentrations (lower than 1:10 ratio risperidone/albumin) were of 2.56 × 10(5)M(-1), at 25 °C, and 1.43 × 10(5)M(-1), at 37 °C. As the quenching intensity of bovine serum albumin, which contains two tryptophan residues, was found to be higher than that of human serum albumin, which contains only one tryptophan residue. Hence, we suggest that the primary binding site for risperidone in albumin should be located in sub domain IB.

Gender differences in the relationship between the risperidone metabolism and the plasma prolactin levels in psychiatric patients

BACKGROUND

Risperidone (RIS) has the highest propensity to elevate plasma prolactin (PRL) levels. While the active metabolite 9-hydroxy-risperidone (9-OH-RIS) plays a predominant role in the efficacy and side effects of RIS, the mechanistic details are still poorly understood. The present study evaluated the gender differences in the relationship between plasma levels of RIS or 9-OH-RIS and PRL.

METHODS

Twenty-one male and 19 female subjects treated with RIS were enrolled in the present series. All patients had been receiving RIS for at least 4 weeks at an average dosage of 4.7 mg/day. Plasma RIS, 9-OH-RIS and PRL levels were measured.

RESULTS

In the male patients, there was no correlation between the RIS dosage and plasma PRL levels, between plasma RIS levels and PRL levels, or between the plasma 9-OH-RIS levels and PRL levels. In the female patients, there was a significant positive correlation between the plasma 9-OH-RIS levels and PRL levels (rs=0.456, p=0.049). There was a trend toward a significant positive correlation between the RIS dosage and plasma PRL levels. There was no correlation between the plasma RIS levels and PRL levels.

CONCLUSION

9-OH-RIS is considered to play a more important role in PRL elevation than RIS, and a gender difference exists in the effect of 9-OH-RIS on PRL level.

Differential effects of olanzapine, haloperidol and risperidone on calcitonin gene-related peptide in the rat brain

Calcitonin gene-related peptide (CGRP) is a 37 amino acid peptide which acts on central nervous system (CNS) neurons and is involved in activities related to dopamine. These effects of CGRP suggest that the peptide may have a role in pathophysiology and treatment of schizophrenia where dopaminergic system hypoactivity in the frontal cortex and hyperactivity in the subcortical structures have been demonstrated. In this study we measured by radioimmunoassay (RIA) the brain levels of CGRP-like immunoreactivity (CGRP-LI) in rats treated with either classical (haloperidol) or atypical (risperidone and olanzapine) antipsychotic drugs. Both haloperidol and risperidone decreased CGRP-LI in the striatum. Risperidone also decreased CGRP-LI in the occipital cortex. On the other hand, olanzapine increased CGRP-LI in the striatum, the frontal cortex and hypothalamus. The differential effects on CGRP could reflect a different profile of side effects and further suggest that CGRP is involved in CNS functions related to psychiatric disorders.

Relationship between prolactin secretion, and plasma risperidone and 9-hydroxyrisperidone concentrations in adolescents with schizophreniform disorder

BACKGROUND

Treatment with the atypical antipsychotic risperidone can result in elevated prolactin levels. To date, the relationships between plasma concentrations of prolactin, risperidone and its active 9-hydroxy-metabolite have been little investigated in adolescents with psychosis.

METHODS

Prolactin levels were determined at baseline in 16 hospitalized drug-naïve adolescents meeting DSM-IV criteria for schizophreniform disorder. Prolactin, risperidone, 9-hydroxyrisperidone levels were subsequently determined after 3 weeks of oral risperidone treatment.

RESULTS

Compared with pretreatment values, prolactin levels at endpoint were significantly increased (p<0.00001) and correlated with risperidone doses (r=0.58, N=16, p<0.02), and plasma levels of risperidone (r=0.60, N=16, p<0.02) and 9-hydroxyrisperidone (r=0.54, N=16, p=0.03).

CONCLUSIONS

These data suggest that risperidone's effect on prolactin release is dose-dependent in adolescents and is linked to both plasma risperidone and 9-hydroxyrisperidone concentrations.

Paliperidone: new drug. Just a metabolite of risperidone, a neuroleptic soon off-patent

(1) For patients with schizophrenia, risperidone is one of many available neuroleptics. It has no tangible advantages over conventional neuroleptics such as haloperidol. (2) Paliperidone, the main active metabolite of risperidone, has now arrived on the European market, in the form of sustained-release osmotic tablets. Clinical evaluation is based on 3 placebo-controlled trials lasting 6 weeks. As expected, paliperidone was effective in relieving symptoms of schizophrenia. However, it was no more effective than olanzapine and has not been compared with risperidone. (3) The adverse effect profile of paliperidone in these trials was predictable, consisting mainly of short-term neurological effects and dose-dependent weight gain. Paliperidone also provokes tachycardia and lengthens the QT interval in some patients. The rigid osmotic tablets can cause gastrointestinal complications. (4) Paliperidone does not represent a therapeutic advance. It is better to continue using a conventional neuroleptic such as haloperidol.

Enantioselective analysis of the antipsychotic 9-hydroxyrisperidone, main metabolite of risperidone, by chiral capillary EKC using dual CDs

An analytical method for the enantioseparation of the 9-hydroxyrisperidone, main metabolite of the antipsychotic risperidone (Risp), was developed by CD-EKC in the dual CDs mode using anionic and neutral CDs at acidic pH 2.5. Preliminary experiments allowed us to select the more suitable couple of CDs composed of sulfated-alpha-CD and hydroxypropylated-beta-CD. The optimization of the main experimental parameters (concentrations of both CDs and concentration of the phosphate buffer) was based on a central composite design through the response surface methodology. Then, the influence of the voltage and the temperature on the enantioseparation was studied using the classical univariate approach. The final method permits to resolve the enantiomers of the 9-hydroxyrisperidone with a resolution of 3.13 and an analysis time of about 13 min. Finally, this method was successfully applied for the simultaneous determination of Risp and the enantiomers of 9-hydroxyrisperidone (9-OHRisp).

Effect of Adjunctive Lamotrigine Treatment on the Plasma Concentrations of Clozapine, Risperidone and Olanzapine in Patients With Schizophrenia or Bipolar Disorder

The effect of lamotrigine on the steady-state plasma concentrations of the atypical antipsychotics clozapine, olanzapine, and risperidone was investigated in patients with schizophrenia or bipolar disorder stabilized on chronic treatment with clozapine (200-500 mg/day; n = 11), risperidone (3-6 mg/day; n = 10) or olanzapine (10-20 mg/day; n = 14)). Lamotrigine was titrated up to a final dosage of 200 mg/day over 8 weeks, and pharmacokinetic assessments were made at baseline and during treatment weeks 6 and 10, at lamotrigine dosages of 100 and 200 mg/day respectively. The plasma concentrations of clozapine, norclozapine, risperidone, and 9-hydroxy-risperidone did not change significantly during treatment with lamotrigine. The mean plasma concentrations of olanzapine were 31 +/- 7 ng/mL at baseline, 32 +/- 7 ng/mL at week 6, and 36 +/- 9 ng/mL at week 10, the difference between week 10 and baseline being statistically significant (P < 0.05). Adjunctive lamotrigine therapy was well tolerated in all groups. These findings indicate that lamotrigine, at the dosages recommended for use as a mood stabilizer, does not affect the plasma levels of clozapine, risperidone, and their active metabolites. The modest elevation in plasma olanzapine concentration, possibly due to inhibition of UGT1A4-mediated olanzapine glucuronidation, is unlikely to be of clinical significance.

Aripiprazole's low intrinsic activities at human dopamine D2L and D2S receptors render it a unique antipsychotic

Aripiprazole is the first clinically approved atypical antipsychotic agent having dopamine D2 receptor partial agonist activities. To evaluate aripiprazole's agonist and antagonist properties, we established a Chinese hamster ovary cell line expressing high and low densities of the long and short isoforms of human dopamine D2 receptors, then compared its properties with 7-{3-[4-(2,3-dimethylphenyl)piperazinyl]propoxy}-2(1H)-quinolinone (OPC-4392), S(-)-3-(3-hydroxyphenyl)-N-n-propylpiperidine ((-)-3-PPP), and terguride (other partial agonists) using forskolin-stimulated cAMP accumulation as an index. In cells expressing high receptor densities, all partial agonists predominantly behaved as agonists. However, in cells expressing low receptor densities, the partial agonists showed significantly lower maximal effects than dopamine. Aripiprazole showed the lowest intrinsic activities. In addition, all compounds blocked the action of dopamine with a maximum effect equal to that of each compound alone. Aripiprazole's low intrinsic activities may account for the clinical finding that, unlike the other partial agonists, it is substantially active against both positive and negative symptoms of schizophrenia.

Metabolic Ratios of Psychotropics as Indication of Cytochrome P450 2D6/2C19 Genotype

The cytochrome P450 enzymes (CYP) 2C19 and 2D6 are involved in the metabolism of many psychotropic drugs. Variability in enzyme activity results in variable metabolic capacities, affecting the metabolism of substrates. The metabolic ratio (MR) of drugs metabolized via these enzymes may therefore reflect the enzyme's activity and/or genotype. To serve as an example for different groups of medications, the selective serotonin reuptake inhibitor venlafaxine, the tricyclic antidepressant amitriptyline, and the antipsychotic risperidone were studied to examine a possible correlation between the MRs of these drugs and the CYP2C19 and/or CYP2D6 genotype. For this purpose data from routine genotyping and serum level analysis were used. The relationships between the observed metabolic ratios and CYP2D6 and/or CYP2C19 genotype were characterized using nonparametric statistical analysis. A clear correlation was observed between the CYP2D6 genotype and the metabolic ratio of venlafaxine. Genotyping of individuals with a log(MR) < -0.6 or a log(MR) > 0.2 would include all patients with an aberrant genotype but would result in a reduction of 52% of genotyping reactions. Slow metabolism of amitriptyline is correlated with a log(MR) > 0.4. Genotyping only those subjects with a log(MR) > 0.4 would result in 88% fewer genotyping reactions. For risperidone, genotyping individuals with a log(MR) > 0.4 would include all CYP2D6 poor metabolizers while reducing the number of genotyping reactions by 93%. According to these data, correlations exist between the log(MR) of venlafaxine, amitriptyline, and risperidone and the genotype of the CYP enzymes involved in their metabolism. From the ranges of log(MR) defined here, a high percentage of aberrant metabolizers can be detected even when patients are not routinely genotyped. Thus, the metabolic ratio may serve as an indication of when genotyping should be considered.

Predominant role of the 9-hydroxy metabolite of risperidone in elevating blood prolactin levels

OBJECTIVE

The atypical antipsychotic risperidone significantly raises plasma prolactin levels in patients, but clozapine, olanzapine, and quetiapine do not. The differences in neuroendocrine response may be connected with the metabolism of the medications. The authors examined the contributory role of risperidone's active metabolite 9-hydroxy-risperidone by measuring plasma concentrations of risperidone, 9-hydroxy-risperidone, and prolactin.

METHOD

Blood samples taken from 25 patients with psychotic disorders following 6 weeks of treatment with risperidone (mean dose=3 mg/day) were examined. Mean plasma concentrations of risperidone, 9-hydroxy-risperidone, and prolactin were 4.6, 19.4, and 49.3 ng/ml, respectively.

RESULTS

The oral dose of risperidone correlated significantly with plasma concentrations of risperidone, 9-hydroxy-risperidone, active moiety, and prolactin. The plasma concentration of 9-hydroxy-risperidone, but not of risperidone, correlated significantly with increases in plasma prolactin.

CONCLUSIONS

These data suggest that the 9-hydroxy metabolite plays a predominant role in risperidone's effect on prolactin release.

Dopamine receptor microdomains involved in molecular recognition and the regulation of drug affinity and function

A cationic protonatable amine moiety on dopaminergic ligands forms a high affinity reinforced ionic bond with an anionic aspartic acid at position 3.32 of dopamine receptors. When present, catechol hydroxyls of the ligands form hydrogen bonds with serines at position 5.42, 5.43, and 5.46, and this network of hydrogen bonds serves to orient ligands in the binding-site crevice and increase their binding affinity. A steric clash between aromatic moieties of the ligands and aromatic amino acids of the receptor (e.g., H6.55, F6.52 or F6.51 and W6.48) is likely to be propagated in domino-like fashion along the length of TM6, which is believed to trigger activation of the receptor. Specifically, it is the change in the conformation of W6.48 from an orientation perpendicular to the plane of the lipid membrane to one that is parallel that is believed to result in activation. Molecular determinants that mediate the D4/D2-selectivity of many extremely D4-selective 1,4-DAP ligands, include a nonconserved cluster of bulky amino acids at the TM2/TM3 interface (positions 2.61, 3.28 and 3.29).

Little Effects of Low Dosage of Levomepromazine on Plasma Risperidone Levels

In the present study, we investigated the effects of levomepromazine on plasma risperidone concentrations in a steady state. Twenty patients taking risperidone at a stable dose for more than 2 weeks who were considered to require levomepromazine coadministration were selected. The scores of excitement in BPRS significantly decreased 2 weeks after the coadministration of levomepromazine. Plasma risperidone concentrations and the ratio of risperidone and 9-hydroxyrisperidone (risperidone/9-hydroxyrisperidone) did not change between before and 2 weeks after the coadministration of levomepromazine. The extrapyramidal symptoms were not worsened by the coadministration of levomepromazine. These results suggest that a low dosage of levomepromazine, use as a sedative adjuvant to risperidone treatment, have no statistically significant effect on the trough plasma concentrations of risperidone.

HPLC-DAD determination of plasma levels of the antipsychotic risperidone and its main metabolite for toxicological purposes

A new, rapid analytical method, based on liquid chromatography with diode array detection, has been developed and applied to the determination of risperidone and its main active metabolite 9-hydroxyrisperidone in human plasma. The chromatographic separation was obtained on a C8 (150 x 4.6 mm, 5 microm) column, using a mobile phase composed of acetonitrile (27%) and a pH 3.0 phosphate buffer (73%). A sample clean-up procedure was carried out by using C8 cartridges and eluting the analytes with methanol. The extraction yield was highly satisfactory for both analytes, with average absolute recovery values of about 95%. The experimental conditions permitted the quantitative determination of risperidone and 9-hydroxyrisperidone with high precision (RSD < 3.6%) and satisfactory sensitivity (LOQ = 4 ng mL(-1)). The method was applied to plasma samples from a patient who had tried to poison himself with 150 mg of risperidone, and was undergoing polypharmacy.

Interpreting Serum Risperidone Concentrations

Risperidone is an atypical antipsychotic commonly used for treatment of schizophrenia and other psychotic disorders. Although therapeutic drug monitoring is not routine for any of the atypical antipsychotics, serum antipsychotic concentrations are measured routinely to assess treatment nonadherence. In humans, risperidone is metabolized by cytochrome P450 2D6 to 9-hydroxyrisperidone; together these constitute the active moiety. Dose-proportional increases in serum concentrations have not been reported for the parent drug, but have been reported for 9-hydroxyrisperidone and the active moiety (i.e., the combined concentrations of risperidone and 9-hydroxyrisperidone). We describe a 34-year-old Caucasian man of Sicilian descent with a history of schizophrenia, disorganized type. He was suspected to be noncompliant with his risperidone therapy. Initially, active moiety risperidone concentrations increased linearly with prescribed dosage increases. However, with continued increases, active moiety concentrations adjusted downward and remained 17-36% below anticipated levels. We propose a method for estimating target active moiety concentrations of risperidone based on dosage-a method that may be used to guide clinicians in assessing nonadherence to risperidone treatment.

High performance liquid chromatographic and thin layer densitometric methods for the determination of risperidone in the presence of its degradation products in bulk powder and in tablets

Two reproducible stability indicating methods were developed for the determination of risperidone (RISP) in presence of its degradation products in pure form and in tablets. The first method was based on reversed phase high performance liquid chromatography (HPLC), on Lichrosorb RP C 18 column (250 mm i.d., 4 mm, 10 microm), using methanol:0.05 M potassium dihydrogen phosphate pH 7 (65:35 (v/v)) as the mobile phase at a flow rate of 1 ml min(-1) at ambient temperature. Quantification was achieved with UV detection at 280 nm over a concentration range of 25-500 microg ml(-1) with mean percentage recovery of 99.87 +/- 1.049. The method retained its accuracy in the presence of up to 90% of RISP degradation products. The second method was based on TLC separation of RISP from its degradation products followed by densitometric measurement of the intact drug spot at 280 nm. The separation was carried out on aluminum sheet of silica gel 60F254 using acetonitrile:methanol:propanol:triethanolamine (8.5:1.2:0.6:0.2 (v/v/v/v)), as the mobile phase, over a concentration range of 2-10 microg per spot and mean percentage recovery of 100.1 +/- 1.18. The two methods were simple, precise, sensitive and could be successfully applied for the determination of pure, laboratory prepared mixtures and tablets. The results obtained were compared with the manufacturer's method.

Long-acting risperidone injection

PURPOSE

The pharmacology, pharmaceutics, clinical efficacy, adverse effects, cost, and dosage and administration of long-acting risperidone injection are reviewed.

SUMMARY

Risperidone is the first atypical antipsychotic available in a long-acting injectable formulation. After a single injection, significant plasma levels of the drug are achieved at week 3 and sustained through week 6, subsiding by weeks 7-8. Steady state is achieved after four injections. Peak levels are less than those seen with comparable doses of oral risperidone. A 12-week double-blind placebo-controlled study and a one-year open-label study demonstrated the efficacy, safety, and tolerability of long-acting risperidone injection in patients with schizophrenia and schizoaffective disorder. Those who were considered stable on their previous medication showed continued clinical improvement and an increase in health-related quality of life during a year of treatment with long-acting risperidone injection. In the 12-week study, risperidone was well tolerated, with adverse-effect rates similar to those seen with placebo. Weight gain with long-acting risperidone injection is similar to that found with oral treatment. Extrapyramidal symptom ratings have shown improvement from baseline following administration of this agent. Individuals with schizophrenia who previously received oral risperidone therapy have shown a reduction in prolactin levels after a switch to the long-acting formulation.

CONCLUSION

With its unique tolerability and efficacy, long-acting risperidone injection has the potential to extend the benefits of assured medication delivery and improved long-term outcomes to more patients with schizophrenia.

The Role of Cytochrome P450 Enzymes in the Metabolism of Risperidone and Its Clinical Relevance for Drug Interactions

In the recent years it has been increasingly recognized that pharmacogenetical factors play an important role in the drug treatment. These factors may influence the appearance of side-effects and drug interactions due to interindividual differences in the activity of metabolizing enzymes. Risperidone in humans is mainly metabolized to 9-hydroxyrisperidone by the polymorphic cytochrome enzyme P450 2D6 (CYP2D6). Plasma concentrations of risperidone and 9-hydroxyrisperidone show large interindividual variability, which may be partly related to the activity of the CYP2D6 enzyme. Around seven percent of Caucasians have a genetically inherited impaired activity of the CYP2D6 enzyme. Debrisoquine metabolic ratio (a marker of CYP2D6 activity) and the number of CYP2D6 active genes have been related to risperidone plasma concentrations among patients during steady-state conditions. A large number drugs have been described to be metabolized by CYP2D6, and it is therefore important to evaluate the clinical significance of the impaired metabolism and possible drug interactions on the enzyme. Since risperidone/9-hydroxyrisperidone ratio strongly correlates with CYP2D6 enzyme activity and the number of CYP2D6 active genes, thus it might be a useful tool in clinical practice to estimate the possible risk of drug interactions due to impaired CYP2D6 enzyme activity. CYP3A4 is the most abundant drug metabolizing enzyme in humans, and in vitro and in vivo results suggest also a role for the enzyme in risperidone metabolism. The consideration of the implication of cytochrome P450 enzymes in risperidone metabolism may help to individualize dose schemes in order to avoid interactions and potentially dangerous side-effects, such us QTc interval lengthening among patients with cardiac risk factors.

A randomized evaluation of the effects of six antipsychotic agents on QTc, in the absence and presence of metabolic inhibition

Many drugs have been associated with QTc prolongation and, in some cases, this is augmented by concomitant administration with metabolic inhibitors. The effects of 6 antipsychotics on the QTc interval at and around the time of estimated peak plasma/serum concentrations in the absence and presence of metabolic inhibition were characterized in a prospective, randomized study in which patients with psychotic disorders reached steady-state on either haloperidol 15 mg/d (n = 27), thioridazine 300 mg/d (n = 30), ziprasidone 160 mg/d (n = 31), quetiapine 750 mg/d (n = 27), olanzapine 20 mg/d (n = 24), or risperidone 6-8 mg/d increased to 16 mg/d (n = 25/20). Electrocardiograms (ECGs) were done at estimated Cmax at steady-state on both antipsychotic monotherapy and after concomitant administration of appropriate cytochrome P-450 (CYP450) inhibitor(s). Mean QTc intervals did not exceed 500 milliseconds in any patient taking any of the antipsychotics studied, in the absence or presence of metabolic inhibition. The mean QTc interval change was greatest in the thioridazine group, both in the presence and absence of metabolic inhibition. The presence of metabolic inhibition did not significantly augment QTc prolongation associated with any agent. Each of the antipsychotics studied was associated with measurable QTc prolongation at steady-state peak plasma concentrations, which was not augmented by metabolic inhibition. The theoretical risk of cardiotoxicity associated with QTc prolongation should be balanced against the substantial clinical benefits associated with atypical antipsychotics and the likelihood of other toxicities.

Transfer of risperidone and 9-hydroxyrisperidone into human milk

OBJECTIVE

To quantify the transfer of risperidone and its active metabolite 9-hydroxyrisperidone into breast milk, estimate the amount the infant receives, measure infant plasma concentrations, and clinically assess the safety of breast feeding during maternal risperidone administration. case summaries: The transfer of risperidone and 9-hydroxyrisperidone into milk was studied in 2 breast-feeding women and one woman with risperidone-induced galactorrhea. Plasma samples were available from 2 of the women and from both breast-fed infants. The milk/plasma concentration ratio determined in 2 women was <0.5 for both compounds. The calculated relative infant "doses" were 2.3%, 2.8%, and 4.7% (as risperidone equivalents) of the maternal weight-adjusted doses. Risperidone and 9-hydroxyrisperidone were not detected in the plasma of the 2 breast-fed infants studied, and no adverse effects were noted.

DISCUSSION

Risperidone therapy is sometimes necessary in breast-feeding women, raising the issue of safety in the exposed infants. Our study shows that the relative infant dose is lower than the arbitrary 10% level of concern. The data provide clear guidance on infant exposure for the cases presented.

CONCLUSIONS

Maternal risperidone therapy is unlikely to be a significant hazard for the breast-fed infant in the short term. Nevertheless, decisions on whether a woman may breast-feed should be made as an individual risk-benefit analysis.

Preliminary evidence of striatal D2 receptor density as a possible biological marker of prognosis in naive schizophrenic patients

With the aim of investigating a possible biological marker of prognosis in schizophrenia, the relationship between striatal dopaminergic D2 receptor (D2R) density and clinical prognostic factors was studied in an initial sample of nine neuroleptic-naive schizophrenic patients. Previous psychosocial adaptation was evaluated by means of the Premorbid Adjustment Scale (PAS). Based on the four DSM-IV criteria in schizophreniform disorder for good prognosis, patients were divided in two groups: good prognosis if > or =2 criteria were met (n=5) and poor prognosis if <2 criteria were met (n=4). D2R density was assessed by means of 123I-IBZM single photon emission computed tomography (SPECT) and striatum/occipital uptake ratios (S/O). S/O ratios previously obtained from a control group of nine age- and sex-matched healthy volunteers were used for comparison.

RESULTS

Patients with poor prognosis showed a higher S/O ratio (mean=1.94, range=1.93-1.98) than patients with good prognosis (mean=1.64, range=1.52-1.79) and the control group (mean=1.69, range=1.51-1.85) [analysis of variance (ANOVA) F=10.628, df=2, P=.001, post hoc Scheffé P<.005]. PAS scores were significantly different between patients with good and poor prognosis (40+/-9.39 vs. 84.25+/-26, Mann-Whitney U-test P=.014). A direct correlation of S/O ratios with PAS scores was found (Spearman r=.72, P=.028).

CONCLUSIONS

Striatal D2R density in naive schizophrenic patients may be related to DSM-IV prognostic factors and premorbid adjustment criteria (PAS). If these preliminary results are confirmed, striatal D2R density might predict premorbid and clinical features associated with poor prognosis in neuroleptic-naive patients.

Long-term pharmacoclinical follow-up in schizophrenic patients treated with risperidone. Plasma and red blood cell concentrations of risperidone and its 9-hydroxymetabolite and their relationship to whole blood serotonin and tryptophan, plasma homovanillic acid, 5-hydroxyindoleacetic acid, dihydroxyphenylethyleneglycol and clinical evaluations

The aim of the study was to establish a relationship between the clinical efficacy of risperidone (Risp), the biological levels of Risp and its metabolite, 9-hydroxyrisperidone (9-OH-Risp), and the turnover of blood biogenic amines during a long-term treatment (1 year). Risp is one of the newer atypical antipsychotic drugs with potent serotonin (5HT2), moderate D2 and real alpha 1-alpha 2 adrenoreceptor antagonistic effects. The study has been performed in an open setting and included 17 patients, but only 15 were followed-up from 3 to 12 months. Pharmacokinetic analyses were conducted at the same time as clinical evaluations, grading using the Positive and Negative Syndrome Scale (PANSS), the Clinical Global Impressions (CGI), the Global Assessment of Functioning Scale (GAF), the Quality of Life Scale (QLS) and the Extrapyramidal Symptoms Rating Scale (ESRS) and the determinations of plasma and red blood cell (RBC) Risp and 9-OH-Risp, whole blood 5HT and tryptophan (Trp), plasma homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5HIAA) and dihydroxyphenylethyleneglycol (DHPG). The therapeutic drug monitoring needed oral Risp daily dose of 4.5 +/- 2.3 mg (range 2-8) and the stabilized concentrations (ng/ml) at endpoint in plasma and RBC were 10 +/- 8 (range 1-23) and 3.5 +/- 2 (range 1-8) for Risp and 29 +/- 19 (range 8-70) and 11.5 +/- 6.6 (range 2.6-22.5) for 9-OH-Risp, respectively. 9-OH-Risp appears to be the major active metabolite compound at higher concentrations than Risp. Positive linear correlations were found only between plasma and RBC 9-OH-Risp and the daily dose and the score of the GAF. Statistically significant clinical results showed that Risp is a potent antipsychotic agent efficacious both on positive and negative symptoms and on quality of life. Positive symptoms decreased after about the second month and the negative symptoms improved secondly. Patients (n = 8) who responded to Risp were characterized, on the long-term, by a statistically significant decrease of whole blood 5HT and increase of plasma DHPG.

Effect of prenatal administration of haloperidol, risperidone, quetiapine and olanzapine on spatial learning and retention in adult rats

The typical antipsychotic haloperidol and atypical antipsychotics olanzapine, quetiapine and risperidone were administered to pregnant Sprague-Dawley dams in the drinking water from Days 8 to 18 of gestation. When the offspring reached adulthood (2 months), spatial learning and short-term retention were examined using the radial arm maze. Results showed that prenatal administration of haloperidol, risperidone and quetiapine impaired learning but only haloperidol and risperidone disrupted short-term retention.

Effects of haloperidol and risperidone on neurotensin levels in brain regions and neurotensin efflux in the ventral striatum of the rat

Neurotensin (NT) may play a role in the pathophysiology of schizophrenia and in the mechanism of action of antipsychotic drugs. Here we studied the effects of a 30-day regimen of haloperidol (1.15 mg/100 g food) and risperidone (1.15 and 2.3 mg/100 g food) on NT-like immunoreactivity (-LI) levels in brain tissue and NT-LI efflux in the ventral striatum (VSTR) of the rat. Haloperidol, but not risperidone, increased NT-LI levels in the striatum. In the occipital cortex, risperidone, but not haloperidol, decreased levels of NT-LI. In the hippocampus and the frontal cortex both haloperidol and risperidone (the higher dose) increased NT-LI levels. In the VSTR, haloperidol and risperidone (the higher dose) decreased NT-LI efflux and abolished the stimulatory effect of d-amphetamine (1.5 mg/kg, s.c.). Thus, changes in NT occur in response to antipsychotic drugs and psychostimulants that may be relevant for the pathophysiology and treatment of schizophrenia.

Cytochrome P450 2D6 deficiency and its clinical relevance in a patient treated with risperidone

In contrast to several authors who found hepatic cytochrome P 450 2D6 (CYP2D6) metabolising status to be clinically unimportant in treatment with the CYP2D6 substrate, risperidone, we report on a 17-year-old schizophrenic patient who suffered from severe extrapyramidal side effects (EPS) while being treated with risperidone at 4 mg per day. He was genotyped as a CYP2D6 poor metaboliser (PM). The active moiety of risperidone (sum of risperidone and 9-hydroxyrisperidone) was elevated and increased even further under co-medication with haloperidol and biperiden. We conclude that the PM phenotype for CYP2D6 of this patient had major clinical importance in treatment with risperidone. Most likely metabolic pathways other than CYP2D6 were also involved that are probably inhibited by haloperidol.

In vivo and in vitro myocardial binding of risperidone and 9-hydroxyrisperidone

Antipsychotic drugs have been found to prolong the QT interval, a phenomenon that, when severe, may facilitate the occurrence of complex ventricular arrhythmia such as torsade de pointes. Concentration-dependent QT prolongation has been demonstrated in vitro with such recent drugs as risperidone on Purkinje fibers and in isolated feline hearts. In vivo, there appears to be a relationship between plasma levels and QTc prolongation. This study was designed to estimate cardiac levels in vivo during treatment. For that purpose, we examined both in vivo and in vitro the ratio between plasma and cardiac tissue concentrations of risperidone and its active metabolite 9-hydroxyrisperidone. Binding parameters for different concentrations were determined in vitro by equilibrium dialysis. In vivo, they were determined by intraperitoneal administration of three doses in the guinea pig. Drug concentrations were determined by a high-performance liquid chromatography method with UV detection developed for that purpose. For risperidone, plasma protein binding varied from 67 to 43% and cardiac homogenate binding varied from 90 to 78%. 9-Hydroxyrisperidone values were lower. Tissue levels were 4.5-fold higher than plasma levels. Binding parameters were similar both in vivo and in vitro. From this model, the relevance of in vitro electrophysiological studies to clinical plasma concentrations can be approached.

No effect of reboxetine on plasma concentrations of clozapine, risperidone, and their active metabolites

The effect of reboxetine on steady-state plasma concentrations of the atypical antipsychotics clozapine and risperidone was studied in 14 patients with schizophrenia or schizoaffective disorder with associated depressive symptoms. Seven patients stabilized on clozapine therapy (250-500 mg/day) and seven receiving risperidone (4-6 mg/day) were given additional reboxetine (8 mg/day). After 4 weeks of reboxetine therapy, mean plasma concentrations of clozapine, norclozapine, and risperidone active moiety (sum of concentrations of risperidone and 9-hydroxyrisperidone) increased slightly but not significantly by 5%, 2%, and 10%, respectively. The mean plasma clozapine/norclozapine and risperidone/9-hydroxyrisperidone ratios were not modified during reboxetine treatment. Reboxetine coadministration with either clozapine or risperidone was well tolerated. These findings indicate that reboxetine has minimal effects on the metabolism of clozapine and risperidone and may be added safely to patients receiving maintenance treatment with these two antipsychotics.

Different enantioselective 9-hydroxylation of risperidone by the two human CYP2D6 and CYP3A4 enzymes

The antipsychotic agent risperidone, is metabolized by different cytochrome P-450 (CYP) enzymes, including CYP2D6, to the active 9-hydroxyrisperidone, which is the major metabolite in plasma. Two enantiomers, (+)- and (-)-9-hydroxyrisperidone might be formed, and the aim of this study was to evaluate the importance of CYP2D6 and CYP3A4/CYP3A5 in the formation of these two enantiomers in human liver microsomes and in recombinantly expressed enzymes. The enantiomers of 9-hydroxyrisperidone were analyzed with high pressure liquid chromatography using a chiral alpha-1 acid glycoprotein column. A much higher formation rate was observed for (+)-9-hydroxyrisperidone than for (-)-9-hydroxyrisperidone in microsomes prepared from six individual livers. The formation of (+)-9-hydroxyrisperidone was strongly inhibited by quinidine, a potent CYP2D6 inhibitor, whereas ketoconazole, a CYP3A4 inhibitor, strongly inhibited the formation of (-)-9-hydroxyrisperidone. Recombinant human CYP2D6 produced only (+)-9-hydroxyrisperidone, whereas a lower formation rate of both enantiomers was detected with expressed CYP3A4 and CYP3A5. In vivo data from 18 patients during treatment with risperidone indicate that the plasma concentration of the (+)-enantiomer is higher than that of the (-)-enantiomer in extensive metabolizers of CYP2D6. These findings clearly suggest that CYP2D6 plays a predominant role in (+)-9-hydroxylation of risperidone, the major metabolic pathway in clinical conditions, whereas CYP3A catalyzes the formation of the (-)-9-hydroxymetabolite. Further studies are required to evaluate the pharmacological/toxic activity of both enantiomers.

Ziprasidone: a novel antipsychotic agent with a unique human receptor binding profile

Ziprasidone is a novel antipsychotic agent with a unique combination of pharmacological activities at human receptors. Ziprasidone has high affinity for human 5-HT receptors and for human dopamine D(2) receptors. Ziprasidone is a 5-HT(1A) receptor agonist and an antagonist at 5-HT(2A), 5-HT(2C) and 5-HT(1B/1D) receptors. Additionally, ziprasidone inhibits neuronal uptake of 5-HT and norepinephrine comparable to the antidepressant imipramine. This unique pharmacological profile of ziprasidone may be related to its clinical effectiveness as a treatment for the positive, negative and affective symptoms of schizophrenia with a low propensity for extrapyramidal side effects, cognitive deficits and weight gain.

Higher occupancy of muscarinic receptors by olanzapine than risperidone in patients with schizophrenia. A[123I]-IDEX SPECT study

RATIONALE

In vitro data have shown anticholinergic properties of the atypical antipsychotic drug olanzapine. Substantial occupancy of muscarinic receptors may be an explanation for the low incidence of extrapyramidal side effects induced by olanzapine.

OBJECTIVES

To obtain an in vivo measurement of muscarinic receptor occupancy by olanzapine compared with risperidone in patients with schizophrenia stabilised on medication.

METHODS

Five patients with schizophrenia treated with olanzapine and five patients treated with risperidone were studied. Muscarinic receptor occupancy in the striatum and cortex was studied in vivo with SPECT using [123I]-IDEX as a radioligand. SPECT data were compared with those of six healthy subjects.

RESULTS

Patients stabilised on olanzapine showed significantly lower mean (+/-SD) striatal and cortical (1.50+/-0.21 and 1.51+/-0.22, respectively) muscarinic receptor binding ratios of [123I]-IDEX (reflecting higher levels of muscarinic receptor occupancy) than controls (3.91+/-0.61 and 3.65+/-0.70, respectively). Furthermore, [123I]-IDEX binding ratios in patients treated with risperidone were slightly lower than controls, reaching significance only in the striatum (2.99+/-0.27 versus 3.91+/-0.61, for risperidone and controls).

CONCLUSIONS

The substantial occupancy of muscarinic receptors in the striatum and cortex by olanzapine may be an explanation for the low incidence and severity of extrapyramidal side effects of this antipsychotic drug. Furthermore, it may also explain the anticholinergic side effects of olanzapine.

Differential effects of subchronic treatments with atypical antipsychotic drugs on dopamine D2 and serotonin 5-HT2A receptors in the rat brain

The effects of 3-week treatment with a typical antipsychotic drug chlorpromazine and three atypical antipsychotic drugs (risperidone, olanzapine and perospirone) on the binding to dopamine D2 and serotonin 5-HT2A receptors were examined in the rat stratum and frontal cortex, respectively. Subchronic treatment with chlorpromazine (10 mg/kg) and perospirone (1 mg/kg) significantly increased D2 receptors, while no increase was observed with lower dose of chlorpromazine (5 mg/kg), perospirone (0.1 mg/kg), risperidone (0.25, 0.5 mg/kg) or olanzapine (1, 2 mg/kg). On the other hand, 3-week administration of chlorpromazine (5, 10 mg/kg) and olanzapine (1, 2 mg/kg) significantly decreased 5-HT2A receptors, but risperidone (0.25, 0.5 mg/kg) or perospirone (0.1, 1 mg/kg) had no effect. The measurement of in vivo drug occupation for D2 and 5-HT2A receptors using N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) suggested that high occupation of 5-HT2A receptors with lower D2 receptor occupancy might be involved in the absence of up-regulation of D2 receptors after subchronic treatment with some atypical antipsychotic drugs.

Brain-derived neurotrophic factor and tyrosine kinase receptor TrkB in rat brain are significantly altered after haloperidol and risperidone administration

The antipsychotics haloperidol and risperidone are widely used in the therapy of schizophrenia. The former drug mainly acts on the dopamine (DA) D(2) receptor whereas risperidone binds to both DA and serotonin (5HT) receptors, particularly in the neurons of striatal and limbic structures. Recent evidence suggests that neurotrophins might also be involved in antipsychotic action in the central nervous system (CNS). We have previously reported that haloperidol and risperidone significantly affect brain nerve growth factor (NGF) level suggesting that these drugs influence the turnover of endogenous growth factors. Brain-derived neurotrophic factor (BDNF) supports survival and differentiation of developing and mature brain DA neurons. We hypothesized that treatments with haloperidol or risperidone will affect synthesis/release of brain BDNF and tested this hypothesis by measuring BDNF and TrkB in rat brain regions after a 29-day-treatment with haloperidol or risperidone added to chow. Drug treatments had no effects on weight of brain regions. Chronic administration of these drugs, however, altered BDNF synthesis or release and expression of TrkB-immunoreactivity within the brain. Both haloperidol and risperidone significantly decreased BDNF concentrations in frontal cortex, occipital cortex and hippocampus and decreased or increased TrkB receptors in selected brain structures. Because BDNF can act on a variety of CNS neurons, it is reasonable to hypothesize that alteration of brain level of this neurotrophin could constitute one of the mechanisms of action of antipsychotic drugs. These observations also support the possibility that neurotrophic factors play a role in altered brain function in schizophrenic disorders.

A pilot study on risperidone metabolism: the role of cytochromes P450 2D6 and 3A

BACKGROUND

The limited available information on plasma risperidone levels shows a stable relationship between daily doses of risperidone and total plasma concentration (risperidone plus its active metabolite 9-hydroxyrisperidone). The ratio between risperidone and 9-hydroxyrisperidone characterizes cytochrome P450 2D6 (CYP2D6) status. According to the manufacturer, the CYP2D6 genotype or drugs that influence CYP2D6 or other cytochrome P450 isoenzyme activity are not expected to be clinically significant. One case report suggests that CYP3A participates in the metabolism of risperidone.

METHOD

A case series of 13 risperidone patients (the initial case and 12 new cases) who were genotyped for CYP2D6 were followed, and another 20 risperidone patients from a case-control study for the CYP2D6 genotype were reviewed.

RESULTS

The CYP2D6 poor metabolizers, who are enzyme deficient (2/13 in the case series and 3/20 in the case-control study), did not appear to tolerate risperidone well. Drugs affecting CYP3A, in particular powerful inducers and inhibitors, resulted in at least a 2-fold decrease or increase in plasma risperidone levels.

CONCLUSION

The anecdotal nature of this study is clearly a limitation. Drugs influencing CYP3A and CYP2D6 metabolic activity may significantly affect risperidone levels. Thus, plasma level monitoring of risperidone in a clinical setting may be useful, especially if patients are taking multiple medications or a CYP2D6 deficiency is suspected. New prospective studies under more controlled conditions are needed to verify these hypotheses.

Brain 5-HT2A receptor occupancy of deramciclane in humans after a single oral administration--a positron emission tomography study

RATIONALE

Deramciclane fumarate is a new 5-HT2A and 5-HT2C receptor antagonist with putative anxiolytic effects. In the present study the binding of deramciclane to serotonin 5-HT2A receptors in frontal cortex of healthy male volunteers was studied using [11C]-N-methyl spiperone ([11C]-NMSP) and positron emission tomography.

METHODS

The receptor occupancy percentage was assessed by the means of inhibition of [11C]-NMSP from the 5-HT2A receptors in the frontal cortex. Single oral doses of 20, 50 and 150 mg deramciclane were given to three subjects at each dose level (total n = 9). The receptor occupancy was measured before deramciclane and at 3 and 6 h post-dosing except at the 20 mg dose level where only the 3-h measurement was done. The occupancy percentage was calculated with the ratio method using cerebellum as a reference area.

RESULTS

Deramciclane inhibited [11C]-NMSP binding dose and concentration dependently. However, deramasciclane inhibited maximally only 52% of the [11C]-NMSP binding in the frontal cortex, indicating a non-5-HT2A receptor binding component of this radioligand in frontal cortex. On average, specific [11C]-NMSP binding cerebellum ratios below 0.355 were not possible to achieve in this population. The 52% inhibition was regarded to represent near 100% 5-HT2A receptor occupancy. The 50 and 90% receptor occupancies were reached at deramciclane plasma concentrations of 21 ng/ml and 70 ng/ml, respectively.

CONCLUSIONS

Deramciclane penetrates the blood-brain barrier in humans. Deramciclane binds to the 5-HT2A receptors in the frontal cortex in a saturable manner in vivo. Consequently, the increase in deramciclane concentration in plasma above 70 ng/ml will not result in major increase in the 5-HT2A receptor occupancy in the brain.

Drug metabolism and atypical antipsychotics

The introduction of the atypical antipsychotics clozapine, risperidone, olanzapine, quetiapine and sertindole for the treatment of schizophrenia has coincided with an increased awareness of the potential of drug-drug interactions, particularly involving the cytochrome P450 (CYP) enzymes. The current literature describing the pharmacokinetics of the metabolism of these agents, including their potential to influence the metabolism of other medications, is reviewed. Clozapine appears to be metabolized primarily by CYP1A2 and CYP3A4, with additional contributions by CYP2C19 and CYP2D6. In addition, clozapine may inhibit the activity of CYP2C9 and CYP2C19, and induce CYP1A, CYP2B and CYP3A. Risperidone is metabolized by CYP2D6, and possibly CYP3A4. In vitro data indicate that olanzapine is metabolized by CYP1A2 and CYP2D6. Quetiapine is metabolised by CYP3A4 and sertindole by CYP2D6. There is, however, a general paucity of in vivo data regarding the metabolism of the atypical antipsychotics, indicating a need for further research in this area.

Pharmacokinetic-pharmacodynamic modeling of risperidone effects on electroencephalography in healthy volunteers

RATIONALE

CNS-active drugs produce specific electroencephalographic changes and the concentration-effect relationship of antipsychotics may be elucidated by adopting electroencephalography (EEG) as an effect measurement tool.

OBJECTIVE

The purpose of the present study was to determine the concentration-effect relationship of risperidone by assessing the EEG effect after oral administrations of single dose risperidone in healthy young males.

METHODS

Nine healthy male volunteers received a 1 mg single oral dose of risperidone according to a placebo controlled crossover design. Plasma levels of risperidone and its active metabolite 9-hydroxyrisperidone were measured by radioimmunoassay. Quantitative EEG parameters were obtained for each of four frequency bands through spectral EEG analysis. The difference in the absolute power in the delta frequency band for the F3 lead between risperidone and placebo was used as a drug effect parameter. For pharmacokinetic-pharmacodynamic modeling, the hypothetical effect compartment kinetically linked to plasma by a first-order process was postulated. All curve fittings were done with the non-linear curve-fitting program NONLIN.

RESULTS

Our results showed that absolute powers in delta and theta frequency bands were higher for risperidone administration than for placebo at all EEG leads, and the maximum effects were detected at about 3 h after administration of the drug. The hysteresis loop was observed in the plot of plasma concentration of risperidone or sum of risperidone and 9-hydroxyrisperidone (Cp) versus EEG effect for each subject. A linear model adequately described the relationship between the effect compartment concentrations (Ce) and EEG effects, and the two limbs of hysteresis in the Cp-effect plot were collapsed in the Ce-effect plot for risperidone or risperidone plus 9-hydroxyrisperidone.

CONCLUSION

The increases of absolute power for delta and theta frequency bands of EEG were induced by single oral administration of risperidone. The linear PK-PD model fit well with the relationship between effect compartment concentrations (Ce) and EEG effects of risperidone.

D2 and 5-HT2 receptor effects of antipsychotics: bridging basic and clinical findings using PET

The advent of a number of new antipsychotics has been paralleled by efforts to better delineate their mechanisms of action and, in doing so, further our understanding of schizophrenia and its pathophysiology. Technological advances, such as positron emission tomography (PET), have proven to be powerful tools in this process, allowing us to evaluate in vivo models based primarily on in vitro evidence. Combined serotonin-2/dopamine-2 (5-HT2/D2) antagonism represents one such model, and we now have PET evidence available that can be extrapolated to our understanding and clinical use of both conventional and novel antipsychotics.