Influence of age, renal and liver impairment on the pharmacokinetics of risperidone in man

Risperidone plasma levels, clinical response and side-effects

INTRODUCTION

Assessment of the relation between oral risperidone dose, serum drug levels and clinical response may provide important information for rational treatment decisions. Inter-individual differences in the liver cytochrome P450 system, especially in the CYP2D6 subsystem, which account for a significant portion of risperidone metabolism, may also influence plasma drug levels and alter clinical response parameters. We thus prospectively investigated risperidone serum concentrations in relation to clinical efficacy and side-effects and genotyped major CYP2D6 polymorphisms to determine their effect upon these parameters.

METHODS

Neuroleptic monotherapy with risperidone was administered to schizophrenia patients in a 6-week open dose clinical trial. Weekly assessments including CGI and PANSS ratings to assess psychopathology; SAS to assess medication side effects; and blood draws to quantify steady state plasma levels of risperidone and 9-OH-risperidone were carried out. In addition, major CYP2D6 polymorphisms including alleles *4, *6 and *14 were genotyped.

RESULTS

Eighty-two patients were recruited. Mean oral dose of risperidone was 4.3 +/- 0.9 mg. Mean plasma level of both risperidone and 9-OH-risperidone together ("active moiety") was 41.6 +/- 26.6 ng/ml. Significant improvements in PANSS scales and the various subscales ensued. There was a positive linear correlation between active moiety plasma levels and dose (r = 0.291, p = 0.015) and between risperidone and 9-OH-risperidone levels (r = 0.262; p = 0.016). Nonresponders to pharmacotherapy (PANSS-Improvement < 30%) showed significantly higher active moiety plasma levels (49.9 +/- 30.7 ng/ml) than responders (38.2 +/- 17.0 ng/ml; p = 0.045) without significantly higher oral doses (p = 0.601). Patients with longer illness duration (> or = 3 years) had significantly higher plasma drug levels than those with a shorter course (< 3 years; p = 0.039). Extrapyramidal side effects (EPS) and plasma levels were not correlated (r = 0.028; p = 0.843), but higher plasma levels at week 2 predicted an incidence for EPS (p < 0.050). Accordingly, patients initially receiving higher oral doses of risperidone were significantly more likely to respond with EPS in the trial course. Eight patients (9.8%) were heterozygous carriers of the CYP2D6 allele *4. CYP2D6 polymorphisms did not predict clinical response, but predicted a tendential increase in the plasma risperidone to 9-OH-risperidone ratio (0.5 +/- 0.6 vs. 1.9 +/- 1.8; p = 0.120).

DISCUSSION

The major finding was that responders to risperidone treatment had significantly lower blood levels of risperidone and 9-OH risperidone than patients who did not respond to the treatment despite administration of similar oral doses. The observed CYP2D6 polymorphisms did not contribute to altered clinical efficacy, but affected risperidone to 9-OH-risperidone ratios. Increased plasma levels of the active moiety in patients with longer illness may represent general aging effects. Conversely, the observed higher plasma levels in nonresponders may derive from unaccounted genetic metabolism abnormalities or Phase II metabolism disturbances. Patients initially receiving higher oral risperidone doses were more likely to respond with extrapyramidal side effects which reaffirms the need for careful titration. The high inter-individual variability in risperidone and 9-OH-risperidone metabolization and the relationship between clinical outcome and plasma levels warrants regular plasma level monitoring of both compounds to assess for the clinically relevant active moiety.

Risperidone: a review of its use in the treatment of bipolar mania

Risperidone (Risperdal) is an atypical antipsychotic with high affinity for 5-hydroxytryptamine (5-HT)2A, dopamine D2 and alpha1- and alpha2-adrenergic receptors. Risperidone is now approved in the UK and the US for use in bipolar mania. Risperidone < or =6 mg/day, as monotherapy or adjunctive therapy with first-line mood stabilisers, significantly improves moderate and severe bipolar mania and improves global functioning over 3 weeks. Improvements in Young Mania Rating Scale (YMRS) scores in double-blind trials were greater with risperidone than with placebo over 3 weeks, and similar to those with haloperidol over 3 and 12 weeks. Risperidone was reasonably well tolerated. Limited data are available on the combination of risperidone and carbamazepine. Risperidone, as monotherapy or combined therapy with lithium or valproate semisodium, is an effective treatment option in bipolar mania.

Influence of age and gender on risperidone plasma concentrations

There is limited information on gender- and age-specific effects on plasma concentrations of risperidone and its active metabolite, 9-hydroxyrisperidone. The present study investigated dose- and weight-adjusted plasma concentrations of risperidone and its metabolite in three age groups (45 years, 45-60 years, over 60 years). Gender-specific differences were examined in the whole sample and for the premenopausal subgroup. One hundred and twenty-nine patients (18-93 years) were included in the study, 52 (40%) male and 77 (60%) female. Concentrations of risperidone and 9-hydroxyrisperidone were measured at steady-state by high-performance liquid chromatography with electrochemical detection (HPLC-ED). When total plasma concentrations (risperidone plus 9-hydroxyrisperidone) were adjusted for daily maintenance dose (ng/mL/mg C/D ratio), significant differences between all age groups were found. We found a mean increase of the C/D ratio by 34.8% per decade in patients older than 42 years. No significant sex-related differences in the average plasma concentrations were observed for the whole sample and for the premenopausal subgroup. This study shows clear evidence of higher risperidone total plasma concentrations for patients over 40 years of age. This linear increase (over 30% per decade) may then lead to an increased incidence of adverse effects in elderly patients.

Pharmacokinetic dosage guidelines for elderly subjects

Ageing is associated with a decline in drug elimination; hence, using the same doses as in younger adults may result in higher plasma drug concentrations and toxicity. Two approaches are available for dose correction to account for decreased drug elimination. One procedure is based on the extrarenal elimination fraction (Q(0)) and the age-dependent changes in creatinine clearance; the other uses the decline in total drug clearance (CL). Mean values of Q(0) and CL in young and old people are reported for many drugs in the literature and are summarised in this article. Although the pharmacokinetic techniques for dose adjustment in the elderly are useful, they provide only an average dose correction and neglect age-dependent changes in drug bio-availability, plasma protein binding, the fate of active metabolites, and altered sensitivity to drugs. To account for pharmacodynamic changes in old age, clinical and/or biochemical targets should be defined as therapeutic goals. Drugs whose effects cannot be monitored in these terms should be avoided in elderly individuals.

Concurrent administration of donepezil HCl and risperidone in patients with schizophrenia: assessment of pharmacokinetic changes and safety following multiple oral doses

AIM

This open-label, multiple-dose trial investigated the effect of concurrent administration of donepezil HCl with risperidone on the pharmacokinetics (PK) and safety profiles of both drugs.

METHODS

Sixteen male patients with schizophrenia, who were receiving stable, physician-optimized risperidone (1-4 mg twice daily), and 15 healthy age- and weight-matched male controls, received donepezil HCl 5 mg daily for 7 days. Patients with schizophrenia remained on their physician-optimized dose of risperidone throughout the study. Pharmacokinetic parameters (C(max), t(max) and AUC) were assessed from plasma drug concentrations measured in blood collected before, during and after administration (for 12 h after risperidone on days 0 and 7, and for 24 h after donepezil HCl on day 7).

RESULTS

The mean age of all the subjects was 38.5 years. Donepezil PK parameters were similar between patients taking donepezil HCl + risperidone (AUC(0-24 h) = 329.0 +/- 17.2 ng x h ml(-1)) and controls taking donepezil HCl alone (AUC(0-24 h) = 354.7 +/- 28.2 ng x h ml(-1)). Pharmacokinetic parameters for risperidone and 9-OH risperidone were not altered in patients with schizophrenia after 7 days of donepezil HCl administration (AUC(0-12 h) standardized by dose: risperidone = 59.6 +/- 16.3 ng.h ml(-1) at day 0, 56.0 +/- 15.8 ng x h ml(-1) at day 7; 9-OH risperidone = 162.1 +/- 19.2 ng x h ml(-1) at day 0, 163.3 +/- 15.0 ng x h ml(-1) at day 7). The most common adverse event in both treatment groups was diarrhoea (6/16 risperidone + donepezil HCl patients and 9/16 donepezil HCl only subjects). There were no significant changes in physical examination, ECG, vital signs or treatment-emergent abnormal laboratory values associated with either of the treatment regimens. No subject developed extrapyramidal side-effects following donepezil administration.

CONCLUSIONS

These results suggest that once-daily dosing of 5 mg donepezil HCl does not alter the PK of risperidone in patients with schizophrenia. The combination of risperidone and donepezil HCl was well tolerated.

Effects of various factors on steady-state plasma concentrations of risperidone and 9-hydroxyrisperidone: lack of impact of MDR-1 genotypes

AIMS

An in vitro study has suggested that risperidone is a substrate of P-glycoprotein, which is coded by MDR-1 gene. Thus, we studied the effects of major polymorphisms of the MDR-1 gene on plasma drug concentrations.

METHODS

Subjects were 85 schizophrenic patients receiving 3 mg twice daily of risperidone. Sample collections were conducted 12 h after the bedtime dosing. Plasma concentrations of risperidone and 9-hydroxyrisperidone were quantified using LC/MS/MS. MDR-1 genotypes (C3435T and G2677T/A) and CYP2D6 genotypes were identified using PCR-RFLP methods.

RESULTS

There was no difference in geometric mean (95% CI) of steady-state plasma concentration of risperidone between C3435T genotypes [C/C, C/T, T/T; 2.06 (1.63, 6.47), 2.96 (3.10, 7.91), 2.28 (1.81, 8.04) ng ml(-1), P = 0.759] or G2677T/A genotypes [G/G, G/T or A, T or A/T or A; 1.62 (0.08, 6.07), 2.64 (3.25, 7.10), 2.71 (2.77, 8.72) ng ml(-1), P = 0.625] or 9-hydroxyrisperidone between C3435T genotypes [38.3 (33.7, 50.1), 34.9 (32.9, 42.0), 35.7 (31.7, 42.3) ng ml(-1), P = 0.715] or G2677T/A genotypes [40.6 (33.0, 51.8), 35.0 (33.3, 42.4), 36.1 (32.8, 47.2) ng ml(-1), P = 0.601]. Multiple regression analyses including CYP2D6 genotypes, sex, and age revealed that steady-state plasma concentration of risperidone correlated with the number of mutated alleles for CYP2D6 (standardized partial correlation coefficients (beta) = 0.540, P < 0.001) and those of 9-hydroxyrisperidone (standardized beta = 0.244, P = 0.038) and active moiety (standardized beta = 0.257, P = 0.027) correlated with age.

CONCLUSIONS

These findings suggest that the MDR-1 variants are not associated with steady-state plasma concentration of risperidone or 9-hydroxyrisperidone, but CYP2D6 genotypes and age are determinants of these concentrations.

Psychotic symptoms in patients with medical disorders

Psychotic symptoms frequently occur in patients with comorbid medical disorders and present a diagnostic and treatment challenge. They may be a part of an independent psychiatric illness associated with the underlying medical condition or induced by substance use or medications. The presence of psychotic symptoms can contribute to misdiagnosis or complicate the management of the comorbid medical illness. Psychiatrists must be familiar with the assessment and management of psychotic disorders in patients with comorbid medical disorders. Medications that may be used to treat psychosis include antipsychotic agents, benzodiazepines, or possibly certain anticonvulsants. Selecting the appropriate medication requires knowledge of the pharmacokinetics of different agents and their side effect profile. Understanding the neuropsychiatric effects of medications and drug-drug interactions may help in preventing psychotic symptoms.

Special considerations in the treatment of patients with bipolar disorder and medical co-morbidities

BACKGROUND: The pharmacological treatment of bipolar disorder has dramatically improved with multiple classes of agents being used as mood-stabilizers, including lithium, anticonvulsants, and atypical antipsychotics. However, the use of these medications is not without risk, particularly when a patient with bipolar disorder also has comorbid medical illness. As the physician who likely has the most contact with patients with bipolar disorder, psychiatrists must have a high index of suspicion for medical illness, as well as a basic knowledge of the risks associated with the use of medications in this patient population. METHODS: A review of the literature was conducted and papers addressing this topic were selected by the authors. RESULTS AND DISCUSSION: Common medical comorbidities and treatment-emergent illnesses, including obesity, diabetes mellitus, dyslipidemia, cardiac disease, hepatic disease, renal disease, pulmonary disease and cancer are reviewed with respect to concomitant use of mood stabilizers. Guidance to clinicians regarding effective monitoring and treatment is offered. CONCLUSIONS: Mood-stabilizing medications are necessary in treating patients with bipolar disorder and often must be used in the face of medical illness. Their safe use is possible, but requires increased vigilance in monitoring for treatment-emergent illnesses and effects on comorbid medical illness.

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 CYP2D6 genotypes on plasma concentrations of risperidone and enantiomers of 9-hydroxyrisperidone in Japanese patients with schizophrenia

It has been shown that risperidone (+)-9-hydroxylation is enantioselectively catalyzed by the polymorphic CYP2D6 in human liver. This study aimed to examine the effect of CYP2D6 genotype on (+)-9-hydroxylation of risperidone in schizophrenic patients. Subjects were 38 Japanese schizophrenic inpatients receiving 6 mg/day of risperidone. Plasma concentrations of risperidone and (+)- and (-)-9-hydroxyrisperidone at steady state were quantified using LC/MS/MS and HPLC with alpha 1 acid-AGP chiral column, respectively. The CYP2D6*5(*5) and *10 alleles were identified using polymerase chain reaction (PCR) methods. Twenty patients had no mutated allele, 14 had one mutated allele, and 4 had two mutated alleles. There were significant differences in the steady-state plasma concentrations of risperidone (ANOVA; p < 0.0001) among the three genotype groups, while the CYP2D6 genotype did not affect the steady-state plasma concentrations of (+)-9-hydroxyrisperidone (p = 0.314) or (-)-9-hydroxyrisperidone (p = 0.957). The concentration ratio of risperidone to 9-hydroxyrisperidone was strongly dependent on the CYP2D6 genotypes. This study suggests that CYP2D6 activity strongly influences the steady-state plasma concentrations of risperidone and risperidone/9-hydroxyrisperidone concentration ratios but is unlikely to determine enantio-selectivity in the steady-state plasma concentrations of 9-hydroxyrisperidone in the clinical situation.

Risperidone and 9-hydroxyrisperidone concentrations are not dependent on age or creatinine clearance among elderly subjects

Risperidone is extensively metabolized to an active metabolite, 9-hydroxyrisperidone (9-OH), which is dependent on renal clearance. Risperidone and 9-OH clearances are reduced in the elderly when compared to young subjects. The objective of this study was to determine whether among elderly subjects, risperidone and 9-OH clearance would further decline with increasing age and decreasing creatinine clearance (CrCl). Twenty geriatric inpatients were evaluated in a naturalistic setting with regard to total daily risperidone dose and dosing interval. Creatinine clearance was determined using an 8-hour urine collection. Risperidone and 9-OH concentrations were determined by radioimmunoassay. Spearman's correlation coefficients were used to examine the impact of age and CrCl on concentrations of risperidone, 9-OH, their sum, and the quotient of 9-OH/risperidone. Mean age was 76.4 +/- 9 years (range 56-91). Mean CrCl was 55.4 +/- 32.8 mL/min/1.73 m2 (range 17-142 mL/min/1.73 m2). Mean risperidone daily dose was 1.3 +/- 0.7 mg. Steady-state risperidone and 9-OH concentrations were 4.1 +/- 5.3 ng/mL and 9.1 +/- 6.2 ng/mL, respectively. Mean 9-OH/risperidone was 6.2 +/- 6.1. Concentrations of risperidone, 9-OH, their sum, and 9-OH/risperidone were not significantly correlated with age or CrCl. These results were unchanged when concentrations were corrected for total daily risperidone dose. Among elderly subjects, risperidone and 9-OH clearance do not decline with increasing age or declining CrCl.

Would a switch from typical antipsychotics to risperidone be beneficial for elderly schizophrenic patients? A naturalistic, long-term, retrospective, comparative study

Elderly chronic schizophrenia patients are particularly difficult to treat because of aging-related changes, cognitive impairment, and comorbid physical illness. This article describes a naturalistic, retrospective study of typical antipsychotic treatment versus risperidone for elderly psychotic inpatients. Fifty-one patients, mean age 72.7 + 5.9 years, mean disease duration 33.1 + 12.0 years, who met the DSM-IV criteria for schizophrenia or schizoaffective disorder were treated by risperidone (n = 26) or typical antipsychotic treatment (n = 25) during acute exacerbation and followed up for 18 months. Patients were rated using the clinical global impression (CGI) scale and positive and negative symptom scale (PANSS), and their body weight was recorded at baseline, 6 months, and 18 months. Both treatment groups improved on all rating scales at 18 months. Levels of decrease in PANSS positive and total scores were more prominent in patients treated with risperidone (p < 0.01 and p < 0.05, respectively). The change in CGI scores reached significance only after 18 months and was more pronounced in the risperidone group (p < 0.01). Anti-Parkinsonian medications were used more frequently in the typical antipsychotic group, whereas benzodiazepines were used more frequently in the risperidone group. Body mass index increased minimally after 18 months in the risperidone group (+ 0.3 kg/m2), whereas a larger (+ 1.1 kg/m2), albeit not statistically significant, increase was recorded in the typical antipsychotic group. Emergence of side effects was less frequent in patients treated with risperidone (4/26 vs. 16/25 patients, p < 0.01). The results of this study demonstrate that in elderly chronic schizophrenic patients, switching from typical antipsychotics to risperidone is effective and well tolerated.

Risperidone in the treatment of psychoses in the elderly: a case report series

Risperidone is one of the newer atypical antipsychotic agents, which combines potent serotonin and dopamine receptor antagonism. It shows efficacy against the positive and negative symptoms of schizophrenic psychoses and other psychotic conditions, and has a low propensity to cause extrapyramidal side effects. The aim of these case reports in elderly patients is to provide the benefit of personal experience with risperidone to the body of published literature and to demonstrate the types of patients that may benefit from treatment. These cases were compiled retrospectively from data collected on referral and during routine hospital appointments. This series covers four main areas of concern when treating the elderly: low-maintenance dosing minimising the likelihood of adverse events; successful treatment of patients previously uncontrolled and experiencing side effects with other antipsychotics; the possibility of intermittent rather than continuous treatment; and the benefits to patients, carers and the health services. At low doses, risperidone is an effective and well-tolerated treatment for psychoses in elderly patients that improves the quality of life for both patients and their caregivers.

The efficacy and safety of risperidone for the treatment of geriatric psychosis

Risperidone is an atypical antipsychotic drug which has been suggested to be beneficial for the treatment of elderly patients with psychotic symptoms. In this study, we assessed the short-term efficacy and the safety of risperidone in geropsychiatric inpatients with psychotic symptoms. The sample population included 110 elderly inpatients with psychotic disorders. Assessment for drug efficacy using the Brief Psychiatric Rating Scale, Sandoz Clinical Assessment-Geriatric scale, and Clinical Global Impression scale was conducted at baseline and also at 4 weeks subsequent to risperidone treatment commencement. Subsequent to commencing risperidone treatment, 80 patients completed a 4-week therapeutic evaluation. Seventy (87.5%) of the 80 patients experienced mild to substantial improvement using the Clinical Global Impression scale. Adverse effects were monitored in all 110 patients. The most commonly detected adverse effects were weakness of legs or walking problems (43/110; 39.1%) and dizziness (32/110; 29.1%). Peripheral edema was noted in 18 (16.4%) patients. Risperidone, in low doses, appeared to have been effective in this sample of patients older than 65 years with psychotic symptoms. The mean dose (2.1 +/- SD 1.4 mg/day) applied was lower then that suggested for young patients and was related to the each specific patient diagnosis. Peripheral edema and walking problems were commonly observed adverse effects for these elderly patients, such problems having not been seen to the same extent in previous studies of young patients.

Plasma Concentrations of Risperidone and 9-Hydroxyrisperidone During Combined Treatment With Paroxetine

SUMMARY

The effects of paroxetine on steady-state plasma concentrations of risperidone and its active metabolite 9-hydroxyrisperidone (9-OH-risperidone) were studied in 10 patients with schizophrenia or schizoaffective disorder. Patients stabilized using risperidone therapy (4-8 mg/d) also received paroxetine (20 mg/d) for 4 weeks. During paroxetine administration, mean plasma concentrations of risperidone increased significantly (P < 0.01), whereas levels of 9-OH-risperidone decreased slightly but not significantly. After 4 weeks of paroxetine treatment, the sum of the concentrations of risperidone and 9-OH-risperidone (active moiety) increased significantly by 45% (P < 0.05) over baseline. The mean plasma risperidone/9-OH-risperidone ratio was also significantly modified (P < 0.001) during paroxetine treatment. The drug combination was generally well tolerated with the exception of one patient who developed Parkinsonian symptoms in the second week of adjunctive therapy. In this patient total plasma levels of risperidone and its active metabolite increased by 62% during paroxetine co-administration. The authors' findings indicate that paroxetine, a potent inhibitor of CYP2D6, may impair the elimination of risperidone, primarily by inhibiting CYP2D6-mediated 9-hydroxylation and to a lesser extent by simultaneously affecting the further metabolism of 9-OH-risperidone or other pathways of risperidone biotransformation. Careful clinical observation and possibly monitoring of plasma risperidone levels may be useful whenever paroxetine is co-administered with risperidone.

Long-term treatment of chronic schizophrenia with risperidone: a study with plasma levels

Twenty-four chronic schizophrenic outpatients with a mean age of 37.21 years +/- 9.96 SD were treated with risperidone (RSP) at the dosage of 2-9 mg/die (mean 4.46 mg/die +/- 1.30 SD, mean 0.06 mg/kg +/- 0.01 SD) for a year. Clinical evaluation was assessed with the Brief Psychiatric Rating Scale (BPRS), Positive and Negative Symptoms Scale (PANSS), Extrapyramidal Side Effects Rating Scale (EPSE) and a checklist for Anticholinergic Side Effects (ACS) at T0, then after 1 (T1), 2 (T2), 3 (T3), 6 (T6), 9 (T9) and 12 (T12) months. RSP and 9-hydroxy-risperidone (9OH-RSP) plasma levels were determined at T12 by the HPLC method. BPRS and PANSS mean values showed a significant improvement during the study. No correlation between RSP dosage (mg/kg) and RSP, 9OH-RSP plasma levels or active moiety resulted. A positive correlation between age and active moiety was observed. A positive correlation between RSP and 9OH-RSP plasma levels was observed. A curvilinear relationship between active moiety and PANSS improvement (%) was observed. Patients with the higher PANSS amelioration showed RSP + 9OH-RSP plasma levels ranging from 15 to 30 ng/mL. RSP seems to be quite an effective drug. It seems, however, difficult to devise appropriate dose schedules and plasma level determination seems to be necessary in some cases.

Determination of risperidone and its major metabolite 9-hydroxyrisperidone in human plasma by reversed-phase liquid chromatography with ultraviolet detection

A simple and sensitive high-performance liquid chromatographic (HPLC) method with UV absorbance detection is described for the quantitation of risperidone and its major metabolite 9-hydroxyrisperidone in human plasma, using clozapine as internal standard. After sample alkalinization with 1 ml of NaOH (2 M) the test compounds were extracted from plasma using diisopropyl ether-isoamylalcohol (99:1, v/v). The organic phase was back-extracted with 150 microl potassium phosphate (0.1 M, pH 2.2) and 60 microl of the acid solution was injected into a C18 BDS Hypersil analytical column (3 microm, 100x4.6 mm I.D.). The mobile phase consisted of phosphate buffer (0.05 M, pH 3.7 with 25% H3PO4)-acetonitrile (70:30, v/v), and was delivered at a flow-rate of 1.0 ml/min. The peaks were detected using a UV detector set at 278 nm and the total time for a chromatographic separation was about 4 min. The method was validated for the concentration range 5-100 ng/ml. Mean recoveries were 98.0% for risperidone and 83.5% for 9-hydroxyrisperidone. Intra- and inter-day relative standard deviations were less than 11% for both compounds, while accuracy, expressed as percent error, ranged from 1.6 to 25%. The limit of quantitation was 2 ng/ml for both analytes. The method shows good specificity with respect to commonly prescribed psychotropic drugs, and it has successfully been applied for pharmacokinetic studies and therapeutic drug monitoring.

Plasma concentrations of risperidone and 9-hydroxyrisperidone: effect of comedication with carbamazepine or valproate

To evaluate the pharmacokinetic interaction between risperidone and the mood-stabilizing agents carbamazepine and valproic acid, steady state plasma concentrations of risperidone and 9-hydroxyrisperidone (9-OH-risperidone) were compared in patients treated with risperidone alone (controls, n = 23) and in patients comedicated with carbamazepine (n = 11) or sodium valproate (n = 10). The three groups were matched for sex, age, body weight, and antipsychotic dosage. Plasma concentrations of risperidone and 9-OH-risperidone did not differ between valproate-comedicated patients and controls. By contrast, the concentrations of both compounds were lower in patients taking carbamazepine, although the difference reached statistical significance only for the metabolite (p < 0.001). The sum of the concentrations of risperidone and 9-OH-risperidone in patients receiving carbamazepine (median 44 nmol/L) was also significantly lower than in patients receiving valproate (168 nmol/L) and in controls (150 nmol/L). In five patients assessed with and without carbamazepine comedication, dose-normalized plasma risperidone and 9-OH-risperidone concentrations were significantly lower when the patients received combination therapy than when they received risperidone alone. In three patients assessed with and without valproate, no major changes in the levels of risperidone and its metabolite were observed. These findings demonstrate that carbamazepine markedly decreases the plasma concentrations of risperidone and its active 9-OH-metabolite, probably by inducing CYP3A4-mediated metabolism. This interaction is likely to be clinically significant. Conversely, valproic acid does not cause any major change in plasma antipsychotic levels.

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.

Age-related changes in protein binding of drugs: implications for therapy

The plasma protein binding of drugs, particularly those that are highly bound, may have significant clinical implications. Although protein binding is a major determinant of drug action, it is only one of a myriad of factors that influence drug disposition. The extent of protein binding is a function of drug and protein concentrations, the affinity constant for the drug-protein interaction and the number of protein binding sites per class of binding site. Age-related changes in protein binding are usually not clinically important in drug therapy. Albumin levels are generally decreased in the elderly, whereas alpha1-acid glycoprotein levels are not altered by age per se. Alterations in plasma protein binding that occur in the elderly are generally not attributed to age, but rather to physiological and pathophysiological changes or disease states that may occur more frequently in the elderly and most often account for altered protein binding. Age-related physiological changes, such as decreased renal function, decreased hepatic function and decreased cardiac output, generally produce more clinically significant alterations in drug disposition than that seen with alterations in drug plasma protein binding. An understanding of the inter-relationships between drug concentrations, protein binding, the physiology of aging, disease, pharmacokinetics and pharmacodynamics is necessary for effective therapeutic monitoring. Monitoring of unbound drug concentrations simplifies these relationships and provides the fundamental information needed for dosage regimen development and adjustment. Drug therapy in the elderly should be individualised taking into account all of these factors.

The pharmacokinetics of ziprasidone in subjects with normal and impaired renal function

AIMS

To assess whether renal impairment influences the pharmacokinetics of ziprasidone, and to determine whether ziprasidone is cleared via haemodialysis.

METHODS

Thirty-nine subjects with varying degrees of renal impairment were enrolled into an open-label, multicentre, multiple-dose study and assigned to four groups according to their renal function: normal (group 1, creatinine clearance > 70 ml min(-1); mildly impaired (group 2, creatinine clearance 30-60 ml min(-1); moderately impaired (group 3, creatinine clearance 10-29 ml min(-1), and severely impaired (group 4, requiring haemodialysis three times-a-week). Subjects received ziprasidone 40 mg day(-1), given orally with food, as two divided daily doses for 7 days and a single 20 mg dose on the morning of day 8. Pharmacokinetic variables were determined from multiple venous blood samples collected on days 1 and 8 (haemodialysis day for subjects with severe renal impairment). Additional samples were collected from subjects with severe renal impairment on day 7 (nonhaemodialysis day).

RESULTS

On day 1 there were no statistically significant differences in the pharmacokinetics (AUC(0, 12 h), Cmax, tmax) of ziprasidone among subjects with normal renal function and those with mild, moderate and severe renal impairment. The AUC(0,12 h) and Cmax in subjects with mildly impaired renal function were statistically significantly greater than in those with moderately impaired renal function (P = 0.0163-0.0385). The mean AUC(0,12 h) was 272, 370, 250 and 297 ng ml(-1) h in groups 1, 2, 3 and 4, respectively. Corresponding mean Cmax values were 47, 61, 41 and 50 ng ml(-1) and corresponding mean tmax values were 5, 6, 5 and 5 h. On day 8 there were no statistically significant differences in the pharmacokinetics (AUC(0,12 h), Cmax, tmax, lambda(z), Fb) of ziprasidone among subjects with normal renal function and those with moderate or severe renal impairment. The AUC(0,12 h) in subjects with mild renal impairment was statistically significantly greater than those in the other three groups (P = 0.0025-0.0221), but this was not considered clinically significant. The mean AUC(0,12 h) were 446, 650, 389 and 427 ng ml(-1) h in groups 1, 2, 3 and 4, respectively. Corresponding mean Cmax values were 68, 93, 54 and 70 ng ml(-1), corresponding mean tmax values were 4, 5, 4 and 5 h and corresponding mean lambda(z) were 0.14, 0.11, 0.14 and 0.17 h(-1). The mean percentage Fb was 99.84-99.88% across all groups and the mean t(1/2),z ranged from 4.2 to 6.4 h. Comparison of the mean AUC(0,12 h) and Cmax values in subjects with severe renal impairment on day 7 with those on day 8 suggested that haemodialysis does not have a clinically significant effect on the pharmacokinetics of ziprasidone.

CONCLUSIONS

The findings of this study indicate that mild-to-moderate impairment of renal function does not result in clinically significant alteration of ziprasidone pharmacokinetics and therefore does not necessitate dose adjustment.

The pharmacokinetics of ziprasidone in subjects with normal and impaired hepatic function

AIMS

To assess whether hepatic impairment influences the pharmacokinetics of ziprasidone.

METHODS

Thirty subjects with normal hepatic function or a primary diagnosis of clinically significant cirrhosis (Child-Pugh A or B) were enrolled into an open-label, multicentre, multiple-dose study. The subjects with chronic, stable hepatic impairment and the matched control subjects received ziprasidone 40 mg day(-1), given orally with food, as two divided daily doses for 4 days and a single 20 mg dose on the morning of day 5. Pharmacokinetic variables were determined from multiple venous blood samples collected on days 1 and 5. Liver function was evaluated quantitatively using antipyrine.

RESULTS

On day 1 there were no statistically significant differences in the pharmacokinetics (AUC(0,12 h), Cmax, tmax) of ziprasidone between the two groups. On day 5 there were no statistically significant differences in the Cmax or tmax for ziprasidone between the two groups. The mean AUC(0,12 h) for ziprasidone was statistically significantly greater in the hepatically impaired subjects compared with the normal subjects (590 ng ml(-1) h vs. 467 ng ml(-1) h, P = 0. 042). However, the AUC(0,12 h) increased by only 26% in the cirrhotic group compared with the matched control group. The ziprasidone lambda(z) in the subjects with normal hepatic function was statistically significantly greater than that in the hepatically impaired subjects (P<0.001). There was no correlation between antipyrine lambda(z) and ziprasidone lambda(z) in the subjects with normal hepatic function or in those with hepatic impairment.

CONCLUSIONS

The findings of this study indicate that mild to moderate hepatic impairment does not result in clinically significant alteration of ziprasidone pharmacokinetics.

Single- and multiple-dose pharmacokinetics of ziprasidone in healthy young and elderly volunteers

AIMS

To compare the pharmacokinetics of ziprasidone in healthy young (18-45 years) men and women, and healthy elderly (> or = 65 years) men and women.

METHODS

Eight young men, 11 young women, 8 elderly men and 8 elderly women were given oral ziprasidone 40 mg day(-1), in two evenly divided daily doses, for 7 days, followed by a single 20 mg dose on day 8. Serum samples were collected immediately before the morning dose on days 1-8, for up to 12 h after dosing on day 1 and for up to 96 h after dosing on day 8. The resulting data were used to derive pharmacokinetic parameters of ziprasidone in each age and gender group.

RESULTS

Steady-state serum concentrations of ziprasidone were achieved within 2-3 days. The steady-state pharmacokinetics of ziprasidone, determined 8 days after the initiation of treatment, were similar in the young men, elderly men and young women. Assessment of gender effects by analysis of variance revealed statistically significant differences in Cmax (85 vs. 69 ng ml(-1) and tmax (3.19 vs. 4.81 h) but no differences in AUC(0,12 h) or lambda(z). Assessment of age effects by analysis of variance revealed statistically significant differences in AUC(0,12 h) (560 vs. 465 ng ml(-1) h), Cmax (85 vs. 69 ng ml(-1) and lambda(z) (0.126 vs. 0.197 l h(-1) but no difference in tmax. Assessment of age and gender effects by analysis of covariance, with body weight as the covariate, did not reveal any significant differences. The mean t(1/2), z in the young men, young women, elderly men and elderly women were 3.1, 4.1, 5.7 and 5.3 h, respectively. Standard deviations of the means for the pharmacokinetic parameters for the elderly women tended to be large.

CONCLUSIONS

The influence of age and gender on the pharmacokinetics of ziprasidone is not clinically significant.

Therapeutic drug monitoring of risperidone using a new, rapid HPLC method: reappraisal of interindividual variability factors

Because of the enormous gap between premarketing studies in physically healthy subjects and clinical practice in patients, the present study reconsidered interindividual variability factors affecting risperidone concentrations under routine therapeutic drug monitoring conditions. The study included 92 patients, 27% of whom were 70 years or older. The patients received risperidone orally (dose range, 0.5-11 mg per day) and had concentrations of risperidone and the active metabolite 9-hydroxyrisperidone measured at steady state by a new, rapid, and sensitive method of high-performance liquid chromatography (HPLC). After normalization to a dose of 4 mg/day, median concentrations were 2.9 ng/ml (80% range, 0.9-27.9 ng/ml) for the parent compound and 24.1 ng/ml (80% range, 12.0-57.6 ng/ml) for the metabolite. When considering linear regression models, age was identified as a major source of interindividual variability, with expected increases of 340% and 220% for concentrations of parent compound and metabolite, with age increasing from 20 to 80 years. Body weight provided an additional significant contribution to the variability of 9-hydroxyrisperidone concentration, a 20-kg higher body weight associated with a concentration decrease of 23%. Serotonin-specific reuptake inhibitor (SSRI) comedication (fluoxetine, two patients; citalopram, two patients; paroxetine, one patient; fluvoxamine, one patient) was significantly associated with 4.6-fold higher concentrations of parent compound, in keeping with an inhibitory action on CYP2D6 enzyme. Significantly higher concentrations of 9-hydroxy-risperidone (+ 29%) were also observed in the 17 patients with biperiden comedication. Therapeutic drug monitoring data, collected in patients representative of the population for which the drug was intended, allowed us to quantify the dose reduction needed in elderly patients and thus provided valuable information in addition to the one collected during premarketing studies performed with strict inclusion and exclusion criteria.

Serum concentrations and side effects in psychiatric patients during risperidone therapy

Steady state serum concentrations of risperidone and 9-hydroxyrisperidone (9-OH-risperidone), the active moiety, were measured in 42 patients. The concentration-to-dose ratios (C/D) varied by a factor of 20, from 1.8 to 36.8 (nmol/l)/(mg/24 hours), and 90% of the active moiety was constituted of 9-OH-risperidone. No correlation between the serum concentration of the active moiety and the side effects evaluated by the UKU Side Effect Scale was found. The absence of CYP2D6 (poor metabolizers) or the coadministration of drugs other than benzodiazepines increased the ratio between parent compound and metabolite but did not significantly influence the C/D of the total active moiety. A therapeutic range for serum risperidone has not been established, but 6 mg/day is considered the optimum dose for most patients. The authors found that in 90% of 22 patients administered 6 mg/day risperidone, the serum levels were within 50 to 150 nmol/l.

Simplified high-performance liquid chromatographic method for determination of risperidone and 9-hydroxyrisperidone in serum from patients comedicated with other psychotropic drugs

A HPLC method was developed for determination of risperidone and its therapeutically active main metabolite 9-hydroxyrisperidone in serum. After a single-step liquid-liquid extraction the analytes were separated on a C18 column and measured by UV detection at 280 nm. Inter-day coefficient of variation was <7% for both compounds at serum levels occurring in patients treated with ordinary doses. Studies of analytical interference showed that the most commonly coadministered antidepressants and benzodiazepines did not interfere. Some conventional low dose neuroleptics and clozapine did interfere, but this is of minor importance, because risperidone is intended as an alternative to these drugs.