Population pharmacokinetic analysis for risperidone using highly sparse sampling measurements from the CATIE study.

AIMS: To characterize pharmacokinetic (PK) variability of risperidone and 9-OH risperidone using sparse sampling and to evaluate the effect of covariates on PK parameters. METHODS: PK analysis used plasma samples collected from the Clinical Antipsychotic Trials of Intervention Effectiveness. A nonlinear mixed-effects model was developed using NONMEM to describe simultaneously the risperidone and 9-OH risperidone concentration-time profile. Covariate effects on risperidone and 9-OH risperidone PK parameters were assessed, including age, weight, sex, smoking status, race and concomitant medications. RESULTS: PK samples comprised 1236 risperidone and 1236 9-OH risperidone concentrations from 490 subjects that were available for analysis. Ages ranged from 18 to 93 years. Population PK submodels for both risperidone and 9-OH risperidone with first-order absorption were selected to describe the concentration-time profile of risperidone and 9-OH risperidone. A mixture model was incorporated with risperidone clearance (CL) separately estimated for three subpopulations [poor metabolizer (PM), extensive metabolizer (EM) and intermediate metabolizer (IM)]. Age significantly affected 9-OH risperidone clearance. Population parameter estimates for CL in PM, IM and EM were 12.9, 36 and 65.4 l h(-1) and parameter estimates for risperidone half-life in PM, IM and EM were 25, 8.5 and 4.7 h, respectively. CONCLUSIONS: A one-compartment mixture model with first-order absorption adequately described the risperidone and 9-OH risperidone concentrations. Age was identified as a significant covariate on 9-OH risperidone clearance in this study.

Sex, race, and smoking impact olanzapine exposure.

Response to antipsychotics is highly variable, which may be due in part to differences in drug exposure. The goal of this study was to evaluate the magnitude and variability of concentration exposure of olanzapine. Patients with Alzheimer's disease (n = 117) and schizophrenia (n = 406) were treated with olanzapine as part of the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE). Combined, these patients (n = 523) provided 1527 plasma samples for determination of olanzapine concentrations. Nonlinear mixed-effects modeling was used to determine the population pharmacokinetics of olanzapine, and patient-specific covariates were evaluated as potential contributors to variability in drug exposure. The population mean olanzapine clearance and volume of distribution were 16.1 L/h and 2150 L, respectively. Elimination of olanzapine varied nearly 10-fold (range, 6.66-67.96 L/h). Smoking status, sex, and race accounted for 26%, 12%, and 7% of the variability, respectively (P < .0001). Smokers cleared olanzapine 55% faster than non/past smokers (P < .0001). Men cleared olanzapine 38% faster than women (P < .0001). Patients who identified themselves as black or African American cleared olanzapine 26% faster than other races (P < .0001). Differences in olanzapine exposure due to sex, race, and smoking may account for some of the variability in response to olanzapine.

Determination of ziprasidone in human plasma by liquid chromatography-electrospray tandem mass spectrometry and its application to plasma level determination in schizophrenia patients.

An accurate, rapid and simple liquid chromatography-tandem mass spectrometry (LC-MS-MS) assay method was developed for the determination of ziprasidone (ZIP) in the plasma of schizophrenia patients. A simple one step liquid-liquid extraction with 20% methylene dichloride in pentane was used to isolate ZIP and the internal standard from the plasma matrix. The compounds were separated on a C-18 column by an isocratic elution and the eluted compounds were analyzed by a triple quadrupole mass spectrometer with a TurboIon spray interface using the positive ion atmospheric pressure electrospray ionization method and detected using multiple reaction monitoring mode. The ZIP standard calibration curve was linear over the range of 0.25-500ng/ml when 0.5ml of plasma was used for the analysis (r(2)>0.998). The intra-assay (within-day) and inter-assay (between-day) variations were less than 12% for the spiked standard curve and quality control samples. The absolute extraction efficiency was 82% for ZIP and 68% for INS-RSP. The analysis time for each sample was less than 3min and useful for high turnaround plasma level determinations. This LC-MS-MS assay method for ZIP is highly specific, sensitive, accurate and rapid and is currently being used for the plasma level determination of ZIP in schizophrenia patients treated with various daily oral doses of ZIP. The data showed large inter-individual variations.

Adverse extrapyramidal effects in four horse given fluphenazine decanoate.

CASE DESCRIPTION: 4 racehorses were examined because of markedly abnormal behavior following administration of fluphenazine decanoate. CLINICAL FINDINGS: Clinical signs included restlessness, agitation, profuse sweating, hypermetria, aimless circling, intense pawing and striking with the thoracic limbs, and rhythmic swinging of the head and neck alternating with episodes of severe stupor. Fluphenazine was detected in serum or plasma from all 4 horses. The dose of fluphenazine decanoate administered to 3 of the 4 horses was within the range (25 to 50 mg) routinely administered to adult humans. TREATMENT AND OUTCOME: In 2 horses, there was no response to IV administration of diphenhydramine hydrochloride, but the abnormal behavior in these 2 horses appeared to resolve following administration of benztropine mesylate, and both horses returned to racing. The other 2 horses responded to diphenhydramine administration. One returned to racing. The other was euthanized because of severe neurologic signs, respiratory failure, and acute renal failure. CLINICAL RELEVANCE: Findings indicate that adverse extrapyramidal effects may occur in horses given fluphenazine decanoate. These effects appear to be unpredictable and may be severe and life threatening. Use of fluphenazine decanoate as an anxiolytic in performance horses is not permitted in many racing and horse show jurisdictions, and analytic procedures are now available to detect the presence of fluphenazine in serum or plasma.

Low-dose fluvoxamine as an adjunct to reduce olanzapine therapeutic dose requirements: a prospective dose-adjusted drug interaction strategy.

Despite the advances in antipsychotic pharmacotherapy over the past decade, many atypical antipsychotic agents are not readily accessible by patients with major psychosis or in developing countries where the acquisition costs may be prohibitive. Olanzapine is an efficacious and widely prescribed atypical antipsychotic agent. In theory, olanzapine therapeutic dose requirement may be reduced during concurrent treatment with inhibitors of drug metabolism. In vitro studies suggest that smoking-inducible cytochrome P450 (CYP) 1A2 contributes to formation of the metabolite 4'-N-desmethylolanzapine. The present prospective study tested the hypothesis that olanzapine steady-state doses can be significantly decreased by coadministration of a low subclinical dose of fluvoxamine, a potent inhibitor of cytochrome P450 1A2. The study design followed a targeted "at-risk" population approach with a focus on smokers who were likely to exhibit increased cytochrome P450 1A2 expression. Patients with stable psychotic illness (N = 10 men, all smokers) and receiving chronic olanzapine treatment were evaluated for steady-state plasma concentrations of olanzapine and 4'-N-desmethylolanzapine. Subsequently, olanzapine dose was reduced from 17.5 +/- 4.2 mg/d (mean +/- SD) to 13.0 +/- 3.3 mg/d, and a nontherapeutic dose of fluvoxamine (25 mg/d, PO) was added to regimen. Patients were reevaluated at 2, 4, and 6 weeks during olanzapine-fluvoxamine cotreatment. There was no significant change in olanzapine plasma concentration, antipsychotic response, or metabolic indices (eg, serum glucose and lipids) after dose reduction in the presence of fluvoxamine (P > 0.05). 4'-N-desmethylolanzapine/olanzapine metabolic ratio decreased from 0.45 +/- 0.20 at baseline to 0.25 +/- 0.11 at week 6, suggesting inhibition of the cytochrome P450 1A2-mediated olanzapine 4'-N-demethylation by fluvoxamine (P < 0.05). In conclusion, this prospective pilot study suggests that a 26% reduction in olanzapine therapeutic dose requirement may be achieved by coadministration of a nontherapeutic oral dose of fluvoxamine.

Intra- and interindividual variations in steady-state plasma concentrations of risperidone and 9-hydroxyrisperidone in schizophrenic patients treated chronically with various doses of risperidone.

The intra- and interindividual variability in apparent steady-state plasma levels of risperidone (RSP) and its metabolite 9-hydroxyrisperidone (9-OHRSP) in schizophrenic patients was investigated. Patients (n = 46, age 26.4 +/- 5.3 years) with diagnosed schizophrenia were treated with a fixed daily oral dose of RSP (1-12 mg/d). The steady-state plasma samples from these patients were collected over a period of 5 years and a total of 549 visits. Plasma concentrations of RSP and 9-OHRSP were determined using a highly sensitive and specific LC-MS-MS method with a detection limit of 0.1 ng/mL. All plasma samples had measurable amounts of 9-OHRSP; however, RSP was nondetectable (<0.1 ng/mL) in 18% of the plasma samples. 9-OHRSP levels were, on average, approximately 22 times higher than those of RSP. The plasma levels of RSP and 9-OHRSP varied widely among patients receiving similar doses of RSP, and the intra- and interindividual variations of RSP and 9-OHRSP plasma levels were found to be large. The data indicated that there was no significant change in the steady-state levels of either RSP or 9-OHRSP during the treatment period. Similarly, the dose-normalized concentration did not vary significantly during the treatment period or with the administered dose. The absence of RSP in many plasma samples (<0.1 ng/mL) and presence of 9-OHRSP at severalfold higher concentrations than RSP indicate that measuring plasma levels of RSP alone may lead to erroneous interpretation in plasma level monitoring studies. The current data support the fact that it is important to measure steady-state levels of total active moiety by analyzing both RSP and 9-OHRSP for plasma drug monitoring.

Brain, plasma and tissue pharmacokinetics of risperidone and 9-hydroxyrisperidone after separate oral administration to rats.

RATIONALE: Following an oral dose of risperidone (RSP), concentrations of its major metabolite 9-hydroxyrisperidone (9-OHRSP) were high in plasma and tissues but disproportionately lower in the brain compared to RSP, indicating that 9-OHRSP may have different pharmacokinetic properties. OBJECTIVES: To investigate non-compartmental pharmacokinetics of RSP and 9-OHRSP in plasma, brain and other tissues after separate administration of a single oral dose of 6 mg/kg RSP and 9-OHRSP to rats. METHODS: Plasma, brain, liver, lung, kidney and spleen tissues were collected at pre-dose and at 0.5, 1, 2, 5, 6, 12, 24, 36 and 48 h post-dose, homogenized in saline and assayed for RSP and 9-OHRSP using a sensitive and specific liquid chromatography tandem mass spectrometry method. RESULTS: The concentration-time curve of RSP and 9-OHRSP showed that they were readily absorbed and followed a multiphase elimination pattern. The terminal elimination half-life (t(1/2) ) of RSP after the RSP dose was longest in the liver (17.6 h) and shortest in the spleen (1.2 h). The t(1/2)of 9-OHRSP after the RSP dose was shorter in plasma (3.4 h) and other tissues (approximately 8-11 h) than that for RSP but it was longer in the spleen. However, the t(1/2) of 9-OHRSP after the 9-OHRSP dose was shorter in most tissues as compared to the t(1/2) of 9-OHRSP after the RSP dose. The area under the concentration-time curve (AUC) of RSP and 9-OHRSP was 6-67 times higher in the plasma and tissues than in the brain. AUCs of 9-OHRSP in tissues after the RSP dose were 2-5 times higher than those for RSP, except in the brain, where AUCs of RSP and 9-OHRSP were similar. CONCLUSION: Pharmacokinetics of 9-OHRSP in many tissues were different after RSP and 9-OHRSP doses. The reason for disproportionate brain levels of 9-OHRSP is not clear. The overall exposure to active drug in the brain as represented by AUC was similar after the RSP and 9-OHRSP doses and the 9-OHRSP is probably an equal contributor to the pharmacological actions of RSP.