SSRI-antipsychotic combination in psychotic depression: sertraline pharmacokinetics in the presence of olanzapine, a brief report from the STOP-PD study.

OBJECTIVE: We recently reported an unexpected interaction between olanzapine and sertraline in a population being treated for psychotic depression. Contrary to knowledge of cytochrome p450 interactions sertraline increased apparent clearance of olanzapine by 30%. Here we examined the pharmacokinetics of sertraline in the same population. Existing studies suggest that sertraline apparent clearance is significantly increased in male subjects and suggested an age/sex interaction. METHODS: We studied subjects undergoing combination of sertraline/olanzapine treatment for psychotic depression in the Study of the Pharmacotherapy of Psychotic Depression. Nonlinear mixed effect modelling software was used to examine the sertraline pharmacokinetics, evaluating age, sex, race, and olanzapine exposure as covariates. RESULTS: Eighty-seven subjects (median age 62 years, 28 male subjects, 11 African-Americans) provided 138 samples for sertraline concentration. Olanzapine exposure had a 14.8-fold range. A one compartment model with combined residual error described the sertraline concentration data adequately. Half-life and sex effect on sertraline apparent clearance (males averaging 50% higher (p < 0.005); 96.6 l/h vs 64.8 in female subjects) were similar to previous reports. No other covariate (age, race or olanzapine exposure) had a significant impact on apparent clearance, and no age/sex interaction emerged. CONCLUSION: Sertraline pharmacokinetics were similar to historical descriptions in populations not taking antipsychotics. Unlike our unexpected finding that sertraline increases olanzapine apparent clearance, olanzapine exposure had no impact on sertraline pharmacokinetics. Copyright © 2016 John Wiley & Sons, Ltd.

The Impact of Sertraline Co-Administration on the Pharmacokinetics of Olanzapine: A Population Pharmacokinetic Analysis of the STOP-PD.

BACKGROUND AND OBJECTIVE: Clinical evidence and expert opinion support using a combination of an antipsychotic and an antidepressant when treating major depression with psychotic features. We characterized the impact of sertraline co-administration on olanzapine clearance in psychotic depression using population pharmacokinetic methods. METHODS: The Study of Pharmacotherapy for Psychotic Depression (STOP-PD) randomized 259 participants to olanzapine plus placebo or olanzapine plus sertraline. Olanzapine was started at 2.5-5 mg/day and sertraline at 25-50 mg/day. Doses were increased to a maximum of 20 mg/day for olanzapine and 200 mg/day for sertraline. Up to four olanzapine concentration samples were collected during the 12-week trial and 12-week continuation phase. We used NONMEM (Version VII) for population pharmacokinetic analysis, assessing effects of the covariates sex, African American origin, smoking, age, and sertraline co-administration. RESULTS: Population pharmacokinetic analysis comprised 336 samples from 175 individuals. The structural model published by Bigos et al. was sufficient to describe the olanzapine data adequately: a one-compartment model with first-order absorption and elimination, using an additive residual error structure with the absorption rate constant fixed to 0.5. Sertraline co-administration significantly increased olanzapine apparent clearance (p < 0.005) by 25-35 % depending on the patient characteristics included. Male sex was associated with a significantly increased clearance. Age and race did not have a significant impact on clearance. CONCLUSIONS: Contrary to expectations from the knowledge of cytochrome P450 interactions, sertraline increased olanzapine apparent clearance. Plausible explanations include patients treated with sertraline having poorer adherence to olanzapine, or the impact of sertraline inhibition of transporters resulting in increased intracellular concentrations and thus access to metabolizing enzymes.

Predictors of abdominal pain in depressed pediatric inflammatory bowel disease patients.

BACKGROUND: Pediatric patients with inflammatory bowel disease (IBD) have high rates of abdominal pain. The study aims were to (1) evaluate biological and psychological correlates of abdominal pain in depressed youth with IBD and (2) determine predictors of abdominal pain in Crohn's disease (CD) and ulcerative colitis (UC). METHODS: Seven hundred sixty-five patients aged 9 to 17 years with IBD seen over 3 years at 2 sites were screened for depression. Depressed youth completed comprehensive assessments for abdominal pain, psychological (depression and anxiety), and biological (IBD-related, through disease activity indices and laboratory values) realms. RESULTS: Two hundred seventeen patients with IBD (161 CD, 56 UC) were depressed. One hundred sixty-three (120 CD, 43 UC) patients had complete abdominal pain index scores. In CD, abdominal pain was associated with depression (r = 0.33; P < 0.001), diarrhea (r = 0.34; P = 0.001), erythrocyte sedimentation rate (r = 0.22; P = 0.02), low albumin (r = 0.24; P = 0.01), weight loss (r = 0.33; P = 0.001), and abdominal tenderness (r = 0.38, P = 0.002). A multivariate model with these significant correlates represented 32% of the variance in pain. Only depression (P = 0.03), weight loss (P = 0.04), and abdominal tenderness (P = 0.01) predicted pain for patients with CD. In UC, pain was associated with depression (r = 0.46; P = 0.002) and nocturnal stools (r = 0.32; P = 0.046). In the multivariate model with these significant correlates, 23% of the variance was explained and only depression (P = 0.02) predicted pain. CONCLUSIONS: The psychological state of pediatric patients with IBD may increase the sensitivity to abdominal pain. Thus, screening for and treating comorbid depression may prevent excessive medical testing and unnecessary escalation of IBD medications.

Randomized efficacy trial of two psychotherapies for depression in youth with inflammatory bowel disease.

OBJECTIVE: Pediatric inflammatory bowel disease (IBD) is associated with high rates of depression. This study compared the efficacy of cognitive behavioral therapy (CBT) to supportive nondirective therapy (SNDT) in treating youth with comorbid IBD and depression. METHOD: Youth (51% female and 49% male; age 9-17 years, mean age 14.3 years) with depression and Crohn's disease (n = 161) or ulcerative colitis (n = 56) were randomly assigned to a 3-month course of CBT or SNDT. The primary outcome was comparative reduction in depressive symptom severity; secondary outcomes were depression remission, increase in depression response, and improved health-related adjustment and IBD activity. RESULTS: A total of 178 participants (82%) completed the 3-month intervention. Both psychotherapies resulted in significant reductions in total Children's Depression Rating Scale Revised score (37.3% for CBT and 31.9% for SNDT), but the difference between the 2 treatments was not significant (p = .16). There were large pre-post effect sizes for each treatment (d = 1.31 for CBT and d = 1.30 for SNDT). More than 65% of youth had a complete remission of depression at 3 months, with no difference between CBT and SNDT (67.8% and 63.2%, respectively). Compared to SNDT, CBT was associated with a greater reduction in IBD activity (p = .04) but no greater improvement on the Clinical Global Assessment Scale (p = .06) and health-related quality of life (IMPACT-III scale) (p = .07). CONCLUSION: This is the first randomized controlled study to suggest improvements in depression severity, global functioning, quality of life, and disease activity in a physically ill pediatric cohort treated with psychotherapy. Clinical trial registration information-Reducing Depressive Symptoms in Physically Ill Youth; http://clinical trials.gov; NCT00534911.

Predictors of depression in youth with Crohn disease.

OBJECTIVE: The aim of the study was to determine whether infliximab use and other potential predictors are associated with decreased prevalence and severity of depression in pediatric patients with Crohn disease (CD). METHODS: A total of 550 (n = 550) youth ages 9 to 17 years with biopsy-confirmed CD were consecutively recruited as part of a multicenter randomized controlled trial. Out of the 550, 499 patients met study criteria and were included in the analysis. At recruitment, each subject and a parent completed the Children's Depression Inventory (CDI). A child or parent CDI score ≥  12 was used to denote clinically significant depressive symptoms (CSDS). Child and parent CDI scores were summed to form total CDI (CDIT). Infliximab use, demographic information, steroid use, laboratory values, and Pediatric Crohn's Disease Activity Index (PCDAI) were collected as the potential predictors of depression. Univariate regression models were constructed to determine the relations among predictors, CSDS, and CDIT. Stepwise multivariate regression models were constructed to predict the relation between infliximab use and depression while controlling for other predictors of depression. RESULTS: Infliximab use was not associated with a decreased proportion of CSDS and CDIT after adjusting for multiple comparisons. CSDS and CDIT were positively associated with PCDAI, erythrocyte sedimentation rate, and steroid dose (P < 0.01) and negatively associated with socioeconomic status (SES) (P < 0.001). In multivariate models, PCDAI and SES were the strongest predictors of depression. CONCLUSIONS: Disease activity and SES are significant predictors of depression in youth with Crohn disease.

Depression subtypes in pediatric inflammatory bowel disease.

OBJECTIVE: The association between inflammatory bowel disease (IBD) and depression provides a unique opportunity to understand the relation between systemic inflammation and depressive symptom profiles. METHODS: Youth (n = 226) ages 9 to 17 years with comorbid IBD and depression underwent psychiatric assessment and evaluation of IBD activity. Latent profile analysis (LPA) identified depressive subgroups based on similar responses to the Children's Depression Rating Scale-Revised. Demographic factors, depression severity, anxiety, IBD activity, inflammatory markers, IBD-related medications, and illness perception were evaluated as predictors of profile membership. RESULTS: Mean age was 14.3 years; 75% had Crohn disease; 31% were taking systemic corticosteroids. Mean depressive severity was moderate, whereas IBD activity, which reflects inflammation, was mild. LPA identified 3 subgroups: Profile-1 (mild, 75%) had diverse low-grade depressive symptoms and highest quality of life; Profile-2 (somatic, 19%) had severe fatigue, appetite change, anhedonia, decreased motor activity, and depressed mood with concurrent high-dose steroid therapy and the highest IBD activity; and Profile-3 (cognitive, 6%) had the highest rates of self-reported depressive symptoms, ostomy placements, and anxiety with IBD symptoms in the relative absence of inflammation. CONCLUSIONS: Evidence was found for 3 depression profiles in youth with IBD and depression. Our analyses determined that patients with predominantly somatic or cognitive symptoms of depression comprised 25% of our cohort. These findings may be used to design subgroup-specific interventions for depression in adolescents with IBD and other physical illnesses associated with systemic inflammation.

Effect of age, weight, and CYP2C19 genotype on escitalopram exposure.

The purpose of this study was to characterize escitalopram population pharmacokinetics (PK) in patients treated for major depression in a cross-national, US-Italian clinical trial. Data from the 2 sites participating in this trial, conducted at Pittsburgh (United States) and Pisa (Italy), were used. Patients received 5, 10, 15, or 20 mg of escitalopram daily for a minimum of 32 weeks. Nonlinear mixed effects modeling was used to model the PK characteristics of escitalopram. One- and 2-compartment models with various random effect implementations were evaluated during model development. Objective function values and goodness-of-fit plots were used as model selection criteria. CYP2C19 genotype, age, weight, body mass index, sex, race, and clinical site were evaluated as possible covariates. In total, 320 plasma concentrations from 105 Pittsburgh patients and 153 plasma concentrations from 67 Pisa patients were available for the PK model development. A 1-compartmental model with linear elimination and proportional error best described the data. Apparent clearance (CL/F) and volume of distribution (V/F) for escitalopram without including any covariates in the patient population were 23.5 L/h and 884 L, respectively. CYP2C19 genotype, weight, and age had a significant effect on CL/F, and patient body mass index affected estimated V/F. Patients from Pisa, Italy, had significantly lower clearances than patients from Pittsburgh that disappeared after controlling for patient CYP2C19 genotype, age, and weight. Postprocessed individual empirical Bayes estimates on clearance for the 172 patients show that patients without allele CYP2C19(*)2 or (*)3 (n = 82) cleared escitalopram 33.7% faster than patients with heterogeneous or homogeneous (*)2 or (*)3 ((*)17/(*)2, (*)17/(*)3, (*)1/(*)2, (*)1/(*)3, (*)2/(*)2, (*)2/(*)3, and (*)3/(*)3, n = 46). CL/F significantly decreased with increasing patient age. Patients younger than 30 years (n = 45) cleared escitalopram 20.7% and 42.7% faster than patients aged 30 to 50 years (n = 84) and older than 50 years of age (n = 43), respectively. CYP2C19 genotype, age, and weight strongly influenced the CL/F of escitalopram. These variables may affect patient tolerance of this antidepressant and may provide important information in the effort to tailor treatments to patients' individual needs.

Population pharmacokinetics of perphenazine in schizophrenia patients from CATIE: impact of race and smoking.

The goal of the study was to characterize population pharmacokinetics (PPK) for perphenazine in patients with schizophrenia from the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE). Patients (n = 156) received 8 to 32 mg of perphenazine daily for 14 to 600 days for a total of 421 plasma concentrations measurements. Nonlinear mixed-effects modeling was used to determine PPK characteristics of perphenazine. One- and 2-compartment models with various random effect implementations and mixture distributions were evaluated. Objective function values and goodness-of-fit plots were used as model selection criteria. Age, weight, sex, race, smoking, and concomitant medications were evaluated as covariates. A 1-compartment linear model with proportional error best described the data. The population mean clearance and volume of distribution for perphenazine were 483 L/h and 18 200 L, respectively. Race and smoking status had significant impacts on perphenazine clearance estimates. In addition, the estimated population mean clearance was 48% higher in nonsmoking African Americans than in nonsmoking other races (512 L/h vs 346 L/h). Active smokers eliminated perphenazine 159 L/h faster than nonsmokers in each race. Clearances for smoking African Americans versus smokers in other races were 671 L/h versus 505 L/h, respectively.

The cognitive cost of anticholinergic burden: decreased response to cognitive training in schizophrenia.

OBJECTIVE: Schizophrenia is treated with medications that raise serum anticholinergic activity and are known to adversely affect cognition. The authors examined the relationship between serum anticholinergic activity and baseline cognitive performance and response to computerized cognitive training in outpatients with schizophrenia. METHOD: Fifty-five patients were randomly assigned to either computerized cognitive training or a computer games control condition. A neurocognitive battery based on the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative was performed at baseline and after the intervention. Serum anticholinergic activity, measured at study entry by radioreceptor assay, was available for 49 patients. RESULTS: Serum anticholinergic activity showed a significant negative correlation with baseline performance in verbal working memory and verbal learning and memory, accounting for 7% of the variance in these measures, independent of age, IQ, or symptom severity. Patients in the cognitive training condition (N=25) showed a significant gain in global cognition compared to those in the control condition, but this improvement was negatively correlated with anticholinergic burden. Serum anticholinergic activity uniquely accounted for 20% of the variance in global cognition change, independent of age, IQ, or symptom severity. CONCLUSIONS: Serum anticholinergic activity in schizophrenia patients shows a significant association with impaired performance in MATRICS-based measures of verbal working memory and verbal learning and memory and is significantly associated with a lowered response to an intensive course of computerized cognitive training. These findings underscore the cognitive cost of medications that carry a high anticholinergic burden. The findings also have implications for the design and evaluation of cognitive treatments for schizophrenia.

The effect of reporting methods for dosing times on the estimation of pharmacokinetic parameters of escitalopram.

The objective of this study was to compare population pharmacokinetic models of escitalopram developed from dosage times recorded by a medication event monitoring system (MEMS) versus the reported times from patients with diagnosed depression. Seventy-three patients were prescribed doses of 10, 15, or 20 mg escitalopram daily. Sparse blood samples were collected at weeks 4, 12, 24, and 36 with 185 blood samples obtained from the 73 patients. NONMEM was used to develop a population pharmacokinetic model based on dosing records obtained from MEMS prior to each blood sample time. A separate population pharmacokinetic analysis using NONMEM was performed for the same population using the patient-reported last dosing time and assuming a steady-state condition as the model input. Objective function values and goodness-of-fit plots were used as model selection criteria. The absolute mean difference in the last dosing time between MEMS and patient-reported times was 4.48 +/- 10.12 hours. A 1-compartment model with first-order absorption and elimination was sufficient for describing the data. Estimated oral clearance (CL/F) to escitalopram was statistically insensitive to reported dosing methods (MEMS vs patient reported: 25.5 [7.0%] vs 26.9 [6.6%] L/h). However, different dosing report methods resulted in significantly different estimates on the volume of distribution (V/F; MEMS vs patient reported: 1000 [17.3%] vs 767 [17.5%] L) and the absorption rate constant K(a) (MEMS vs patient reported: 0.74 [45.7%] vs 0.51 [35.4%] h(-1)) for escitalopram. Furthermore, the parameters estimated from the MEMS method were similar to literature reported values for V/F ( approximately 1100 L) and K(a) ( approximately 0.8-0.9 h(-1)) arising from traditional pharmacokinetic approaches.

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.

Anticholinergic activity of 107 medications commonly used by older adults.

The objective of this study was to measure the anticholinergic activity (AA) of medications commonly used by older adults. A radioreceptor assay was used to investigate the AA of 107 medications. Six clinically relevant concentrations were assessed for each medication. Rodent forebrain and striatum homogenate was used with tritiated quinuclidinyl benzilate. Drug-free serum was added to medication and atropine standard-curve samples. For medications that showed detectable AA, average steady-state peak plasma and serum concentrations (C(max)) in older adults were used to estimate relationships between in vitro dose and AA. All results are reported in pmol/mL of atropine equivalents. At typical doses administered to older adults, amitriptyline, atropine, clozapine, dicyclomine, doxepin, L-hyoscyamine, thioridazine, and tolterodine demonstrated AA exceeding 15 pmol/mL. Chlorpromazine, diphenhydramine, nortriptyline, olanzapine, oxybutynin, and paroxetine had AA values of 5 to 15 pmol/mL. Citalopram, escitalopram, fluoxetine, lithium, mirtazapine, quetiapine, ranitidine, and temazepam had values less than 5 pmol/mL. Amoxicillin, celecoxib, cephalexin, diazepam, digoxin, diphenoxylate, donepezil, duloxetine, fentanyl, furosemide, hydrocodone, lansoprazole, levofloxacin, metformin, phenytoin, propoxyphene, and topiramate demonstrated AA only at the highest concentrations tested (patients with above-average C(max) values, who receive higher doses, or are frail may show AA). The remainder of the medications investigated did not demonstrate any AA at the concentrations examined. Psychotropic medications were particularly likely to demonstrate AA. Each of the drug classifications investigated (e.g., antipsychotic, cardiovascular) had at least one medication that demonstrated AA at therapeutic doses. Clinicians can use this information when choosing between equally efficacious medications, as well as in assessing overall anticholinergic burden.

Serotonin transporter genotype interacts with paroxetine plasma levels to influence depression treatment response in geriatric patients.

OBJECTIVE: To investigate whether variable antidepressant response may be influenced by an interaction between the serotonin transporter promoter polymorphism (5-HTTLPR) and antidepressant concentration. METHODS: Elderly subjects with depression treated with paroxetine (n = 110) were genotyped and assessed with the Hamilton Rating Scale for Depression (HAMD). A mixed-effect analysis of repeated measures was used. RESULTS: There was an interaction between early paroxetine concentration and 5-HTTLPR genotype on symptomatic improvement over 12 weeks (F(18,59.5) = 1.8, p < 0.05), as well as main effects of both paroxetine concentration (F(68,55.3) = 2.4, p < 0.005) and genotype (F(2,74.2) = 5.7, p < 0.005). Paroxetine concentrations were correlated with change in HAMD scores after 2 weeks of treatment in subjects with the short (s) allele (r = 0.31, p < 0.05) but not in subjects homozygous for the long (l) allele. CONCLUSION: The results demonstrate a concentration-response relation for paroxetine in late-life depression and support the hypothesis for both a direct main effect and a moderating influence of 5-HTTLPR alleles on this concentration-response relation.

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.

Serum anticholinergic activity and motor performance in elderly persons.

BACKGROUND: Medications prescribed to elderly persons often have an anticholinergic effect, as do many commonly used over-the-counter drugs. Anticholinergic medications are known to produce psychomotor slowing, especially in older persons. METHODS: The present study examined whether the cumulative anticholinergic load present in the serum of community volunteers was associated with decrements on tests of psychomotor performance (gait speed and simple manual response time) known to predict falls in elderly persons. RESULTS: Serum anticholinergic activity (SAA) was relatively low in this group; however, an elevated SAA was associated with a significant slowing in both gait speed and simple response time. CONCLUSION: Cumulative anticholinergic burden may be one of the factors contributing to an increased risk of falls in the older population.

A model of anticholinergic activity of atypical antipsychotic medications.

BACKGROUND: Atypical antipsychotics clozapine, olanzapine, and quetiapine have significant affinity for the muscarinic receptors in vitro, while aripiprazole, risperidone, and ziprasidone do not. Dissimilarity in binding profiles may contribute to the reported differences in the anticholinergic effects of these antipsychotics. However, it is difficult with the available data to predict the likelihood of anticholinergic effects occurring with various doses of an atypical antipsychotic. METHODS: We developed a model to assess the potential anticholinergic activity (AA) of atypical antipsychotics at therapeutic doses. A radioreceptor assay was used to measure in vitro AA at 6 clinically relevant concentrations of aripiprazole, clozapine, olanzapine, quetiapine, risperidone, and ziprasidone. Using published pharmacokinetic data, in combination with the measured in vitro AA, dose-AA curves were generated. RESULTS: Clozapine, and to a lesser extent olanzapine and quetiapine showed dose-dependent increases in AA. At therapeutic doses, the AA (in pmol/mL of atropine equivalents) was estimated to range from 27-250, 1-15, and 0-5.4 pmol/mL for clozapine, olanzapine, and quetiapine, respectively. Aripiprazole, risperidone, and ziprasidone did not demonstrate AA at any of the concentrations studied. CONCLUSIONS: Therapeutic doses of clozapine, olanzapine, and, to a lesser extent, quetiapine are associated with clinically relevant AA.

Population pharmacokinetics as a method to detect variable risperidone exposure in patients suffering from dementia with behavioral disturbances.

OBJECTIVE: This study was intended to compare the consistency of risperidone exposure in patients who have dementia and behavioral disturbances treated in a psychiatric hospital versus a community care setting. METHODS: Population pharmacokinetic modeling was used to assess the consistency of risperidone exposure in Alzheimer's disease patients with agitation. The ratio of predicted to observed drug concentrations (Cpred/Cobs) derived from this model was used to compare exposure in the inpatient versus long-term/home care settings using both the mean and the variance of this term across groups. RESULTS: The modeled Cpred/Cobs ratios had a much higher within-subject variance in the inpatients than in the community care patients (117.03% vs 72.35%; P < 0.001). The central tendencies of the Cpred/Cobs ratios across the 2 groups were not significantly different. CONCLUSIONS: Exposure to risperidone was more variable in a psychiatric hospital than in a community care setting. Future research may help to identify the specific contributors to the increased variance observed in this pilot study.

Utility of sparse concentration sampling for citalopram in elderly clinical trial subjects.

The objective of this study was to evaluate whether the disposition of the selective serotonin reuptake inhibitor, citalopram, could be robustly captured using 1 to 2 concentration samples per subject in 106 patients participating in 2 clinical trials. Nonlinear mixed-effects modeling was used to evaluate the pharmacokinetic parameters describing citalopram's disposition. Both a prior established 2-compartment model and a de novo 1-compartment pharmacokinetic model were used. Covariates assessed were concomitant medications, race, sex, age (22-93 years), and weight. Covariates affecting disposition were assessed separately and then combined in a stepwise manner. Pharmacokinetic characteristics of citalopram were well captured using this sparse sampling design. Two covariates (age and weight) had a significant effect on the clearance and volume of distribution in both the 1- and 2-compartment pharmacokinetic models. Clearance decreased 0.23 L/h for every year of age and increased 0.14 L/h per kilogram body weight. It was concluded that hyper-sparse sampling designs are adequate to support population pharmacokinetic analysis in clinically treated populations. This is particularly valuable for populations such as the elderly, who are not typically available for pharmacokinetic studies.