Pragmatic physiologically-based pharmacokinetic modeling to support clinical implementation of optimized gentamicin dosing in term neonates and infants: proof-of-concept.

Introduction: Modeling and simulation can support dosing recommendations for clinical practice, but a simple framework is missing. In this proof-of-concept study, we aimed to develop neonatal and infant gentamicin dosing guidelines, supported by a pragmatic physiologically-based pharmacokinetic (PBPK) modeling approach and a decision framework for implementation. Methods: An already existing PBPK model was verified with data of 87 adults, 485 children and 912 neonates, based on visual predictive checks and predicted-to-observed pharmacokinetic (PK) parameter ratios. After acceptance of the model, dosages now recommended by the Dutch Pediatric Formulary (DPF) were simulated, along with several alternative dosing scenarios, aiming for recommended peak (i.e., 8-12 mg/L for neonates and 15-20 mg/L for infants) and trough (i.e., <1 mg/L) levels. We then used a decision framework to weigh benefits and risks for implementation. Results: The PBPK model adequately described gentamicin PK. Simulations of current DPF dosages showed that the dosing interval for term neonates up to 6 weeks of age should be extended to 36-48 h to reach trough levels <1 mg/L. For infants, a 7.5 mg/kg/24 h dose will reach adequate peak levels. The benefits of these dose adaptations outweigh remaining uncertainties which can be minimized by routine drug monitoring. Conclusion: We used a PBPK model to show that current DPF dosages for gentamicin in term neonates and infants needed to be optimized. In the context of potential uncertainties, the risk-benefit analysis proved positive; the model-informed dose is ready for clinical implementation.

Physiologically-Based Pharmacokinetic Modeling for Drug Dosing in Pediatric Patients: A Tutorial for a Pragmatic Approach in Clinical Care.

It is well-accepted that off-label drug dosing recommendations for pediatric patients should be based on the best available evidence. However, the available traditional evidence is often low. To bridge this gap, physiologically-based pharmacokinetic (PBPK) modeling is a scientifically well-founded tool that can be used to enable model-informed dosing (MID) recommendations in children in clinical practice. In this tutorial, we provide a pragmatic, PBPK-based pediatric modeling workflow. For this approach to be successfully implemented in pediatric clinical practice, a thorough understanding of the model assumptions and limitations is required. More importantly, careful evaluation of an MID approach within the context of overall benefits and the potential risks is crucial. The tutorial is aimed to help modelers, researchers, and clinicians, to effectively use PBPK simulations to support pediatric drug dosing.

Paleoenvironments shaped the exchange of terrestrial vertebrates across Wallace's Line.

Faunal turnover in Indo-Australia across Wallace's Line is one of the most recognizable patterns in biogeography and has catalyzed debate about the role of evolutionary and geoclimatic history in biotic interchanges. Here, analysis of more than 20,000 vertebrate species with a model of geoclimate and biological diversification shows that broad precipitation tolerance and dispersal ability were key for exchange across the deep-time precipitation gradient spanning the region. Sundanian (Southeast Asian) lineages evolved in a climate similar to the humid "stepping stones" of Wallacea, facilitating colonization of the Sahulian (Australian) continental shelf. By contrast, Sahulian lineages predominantly evolved in drier conditions, hampering establishment in Sunda and shaping faunal distinctiveness. We demonstrate how the history of adaptation to past environmental conditions shapes asymmetrical colonization and global biogeographic structure.

Lamivudine and Emtricitabine Dosing Proposal for Children with HIV and Chronic Kidney Disease, Supported by Physiologically Based Pharmacokinetic Modelling.

Dose recommendations for lamivudine or emtricitabine in children with HIV and chronic kidney disease (CKD) are absent or not supported by clinical data. Physiologically based pharmacokinetic (PBPK) models have the potential to facilitate dose selection for these drugs in this population. Existing lamivudine and emtricitabine compound models in Simcyp® (v21) were verified in adult populations with and without CKD and in non-CKD paediatric populations. We developed paediatric CKD population models reflecting subjects with a reduced glomerular filtration and tubular secretion, based on extrapolation from adult CKD population models. These models were verified using ganciclovir as a surrogate compound. Then, lamivudine and emtricitabine dosing strategies were simulated in virtual paediatric CKD populations. The compound and paediatric CKD population models were verified successfully (prediction error within 0.5- to 2-fold). The mean AUC ratios in children (GFR-adjusted dose in CKD population/standard dose in population with normal kidney function) were 1.15 and 1.23 for lamivudine, and 1.20 and 1.30 for emtricitabine, with grade-3- and -4-stage CKD, respectively. With the developed paediatric CKD population PBPK models, GFR-adjusted lamivudine and emtricitabine dosages in children with CKD resulted in adequate drug exposure, supporting paediatric GFR-adjusted dosing. Clinical studies are needed to confirm these findings.

Physiologically Based Pharmacokinetic (PBPK) Model-Informed Dosing Guidelines for Pediatric Clinical Care: A Pragmatic Approach for a Special Population.

Physiologically based pharmacokinetic (PBPK) modeling can be an attractive tool to increase the evidence base of pediatric drug dosing recommendations by making optimal use of existing pharmacokinetic (PK) data. A pragmatic approach of combining available compound models with a virtual pediatric physiology model can be a rational solution to predict PK and hence support dosing guidelines for children in real-life clinical care, when it can also be employed by individuals with little experience in PBPK modeling. This comes within reach as user-friendly PBPK modeling platforms exist and, for many drugs and populations, models are ready for use. We have identified a list of drugs that can serve as a starting point for pragmatic PBPK modeling to address current clinical dosing needs.

Feasibility of a Pragmatic PBPK Modeling Approach: Towards Model-Informed Dosing in Pediatric Clinical Care.

BACKGROUND AND OBJECTIVE: More than half of all drugs are still prescribed off-label to children. Pharmacokinetic (PK) data are needed to support off-label dosing, however for many drugs such data are either sparse or not representative. Physiologically-based pharmacokinetic (PBPK) models are increasingly used to study PK and guide dosing decisions. Building compound models to study PK requires expertise and is time-consuming. Therefore, in this paper, we studied the feasibility of predicting pediatric exposure by pragmatically combining existing compound models, developed e.g. for studies in adults, with a pediatric and preterm physiology model. METHODS: Seven drugs, with various PK characteristics, were selected (meropenem, ceftazidime, azithromycin, propofol, midazolam, lorazepam, and caffeine) as a proof of concept. Simcyp® v20 was used to predict exposure in adults, children, and (pre)term neonates, by combining an existing compound model with relevant virtual physiology models. Predictive performance was evaluated by calculating the ratios of predicted-to-observed PK parameter values (0.5- to 2-fold acceptance range) and by visual predictive checks with prediction error values. RESULTS: Overall, model predicted PK in infants, children and adolescents capture clinical data. Confidence in PBPK model performance was therefore considered high. Predictive performance tends to decrease when predicting PK in the (pre)term neonatal population. CONCLUSION: Pragmatic PBPK modeling in pediatrics, based on compound models verified with adult data, is feasible. A thorough understanding of the model assumptions and limitations is required, before model-informed doses can be recommended for clinical use.

Poisoning in older adults: characterization of exposures reported to the Dutch Poisons Information Center.

Introduction: The annual number of patients > 65 years old about whom the Dutch Poisons Information Center (DPIC) was consulted has more than doubled in the last decade. We aimed to gain insight in the type and circumstances of exposures reported to the DPIC involving older patients, in order to help prevent future poisonings. Methods: Enquiries to the DPIC involving patients > 65 years old were prospectively included from January 2019 to June 2019. Data were collected on patient characteristics (e.g., age, gender, and living situation) and exposure characteristics (e.g., type and exposure scenario). Results: In the first half of 2019, the DPIC was consulted about 1051 patients > 65 years old. The median age of the patients was 77 years old (range: 66-104 years) and women were over-represented (61%). A total of 1650 different substances were reported, 1213 pharmaceutical exposures (74%) and 437 non-pharmaceutical exposures (26%), mostly household products (n = 162). Most pharmaceutical exposures involved cardiovascular agents (n = 367, 30%), central and peripheral nervous system agents (n = 354, 29%), and analgesics (n = 152, 13%). In 71% of the patients exposed to pharmaceuticals, the drugs were taken unintentionally (n = 471), frequently caused by medication errors made by the patients themselves (n = 357, 76%). Most common scenarios included inadvertently taken/given a double (n = 140, 30%) or more than double (n = 94, 20%) dose or the wrong medication (n = 124, 26%). The most common scenario for unintentional exposure to non-pharmaceuticals was "mistook product for food/drink" (n = 122, 37%). Conclusions: The majority of intoxications in older adults are accidental and often involve medication errors. Unintentional poisoning is often preventable. If patients are cognitively impaired, potentially harmful substances should be kept out of their reach and medication should only be administered under direct supervision. Clear labelling, simplified drug regimens and the use of automatic medication dispensers could reduce the risk of medication errors in older patients.

Off-Label, but on-Evidence? A Review of the Level of Evidence for Pediatric Pharmacotherapy.

Many drugs are still prescribed off-label to the pediatric population. Although off-label drug use not supported by high level of evidence is potentially harmful, a comprehensive overview of the quality of the evidence pertaining off-label drug use in children is lacking. The Dutch Pediatric Formulary (DPF) provides best evidence-based dosing guidelines for drugs used in children. For each drug-indication-age group combination-together compiling one record-we scored the highest available level of evidence: labeled use, systematic review or meta-analysis, randomized controlled trial (RCT), comparative research, noncomparative research, or consensus-based expert opinions. For records based on selected guidelines, the original sources were not reviewed. These records were scored as guideline. A total of 774 drugs were analyzed comprising a total of 6,426 records. Of all off-label records (n = 2,718), 14% were supported by high quality evidence (4% meta-analysis or systematic reviews, 10% RCTs of high quality), 20% by comparative research, 14% by noncomparative research, 37% by consensus-based expert opinions, and 15% by selected guidelines. Fifty-eight percent of all records were authorized, increasing with age from 30% in preterm neonates (n = 110) up to 64% in adolescents (n = 1,630). Many have advocated that off-label use is only justified when supported by a high level of evidence. We show that this prerequisite would seriously limit available drug treatment for children as the underlying evidence is low across ages and drug classes. Our data identify the drugs and therapeutic areas for which evidence is clearly missing and could drive the global research agenda.

The Impact of Interdisciplinary Care on Cost Reduction in a Geriatric Trauma Population.

The current growth of the geriatric population and increased burden on trauma services throughout the United States (US) has created a need for systems that can improve patient care and reduce hospital costs. We hypothesize that the multidisciplinary services provided through the Geriatric Injury Institute (GII) can reduce hospital costs, improve patient triage throughput, and decrease hospital length of stay (LOS). METHODS AND MATERIAL: We performed a single-center, retrospective chart review of our Level II trauma center registry and electronic medical records of patients ages 65 and older who satisfied trauma activation/code criteria between July 1, 2014, to June 30, 2016 (N = 663). Patients presenting from July 1, 2014, to June 30, 2015, were grouped as Pre-GII, while those presenting from July 1, 2015, to June 30, 2016, were grouped as Post-GII. Primary outcomes were emergency department (ED) triage time, overall LOS, and hospital costs. Secondary outcomes included patient disposition, mortality, and health assessments. Statistical comparisons were made using a one-way analysis of variance and Mann-Whitney U test. RESULTS: Pre-GII vs. Post-GII average ages and the Injury Severity Score (ISS) were not statistically different (p>0.05). The average LOS was similar between the Pre-GII and Post-GII groups (4.64 ± 4.42 days vs. 4.26 ± 5.58 days, p = 0.48). More patients were discharged earlier (≤ 4 days; 64% vs. 73%) as well as discharged to home (37% vs. 45%) in the Post-GII group. The total cost savings were $53,000 with a median savings of $1061 per patient ($8808 vs. $7747, p = 0.04). Savings were highest during the first two days of admission (p = 0.03). The reduction in ED triage time was not significant (310.7 minutes vs 219. 8 minutes, p > 0.05). CONCLUSION: With the increase in geriatric trauma, innovative models of care are needed. Our study suggests that the GII multidisciplinary approach to trauma services can lower overall hospital costs.

In-vivo stretch of term human fetal membranes.

INTRODUCTION: Fetal membranes (FM) usually fail prior to delivery during term labor, but occasionally fail at preterm gestation, precipitating preterm birth. To understand the FM biomechanical properties underlying these events, study of the baseline in-vivo stretch experienced by the FM is required. This study's objective was to utilize high resolution MRI imaging to determine in-vivo FM stretch. METHODS: Eight pregnant women (38.4 ± 0.4wks) underwent abdominal-pelvic MRI prior to (2.88 ± 0.83d) caesarean delivery. Software was utilized to determine the total FM in-vivo surface area (SA) and that of its components: placental disc and reflected FM. At delivery, the SA of the disc and FM in the relaxed state were measured. In-vivo (stretched) to delivered SA ratios were calculated. FM fragments were then biaxially stretched to determine the force required to re-stretch the FM back to in-vivo SA. RESULTS: Total FM SA, in-vivo vs delivered, was 2135.51 ± 108.47 cm(2) vs 842.59 ± 35.86 cm(2); reflected FM was 1778.42 ± 107.39 cm(2) vs 545.41 ± 22.90 cm(2), and disc was 357.10 ± 28.08 cm(2) vs 297.18 ± 22.14 cm(2). The ratio (in-vivo to in-vitro SA) of reflected FM was 3.26 ± 0.11 and disc was 1.22 ± 0.10. Reflected FM re-stretched to in-vivo SA generated a tension of 72.26 N/m, corresponding to approximate pressure of 15.4 mmHg. FM rupture occurred at 295.08 ± 31.73 N/m corresponding to approximate pressure of 34 mmHg. Physiological SA was 70% of that at rupture. DISCUSSION: FM are significantly distended in-vivo. FM collagen fibers were rapidly recruited once loaded and functioned near the failure state during in-vitro testing, suggesting that, in-vivo, minimal additional (beyond physiological) stretch may facilitate rapid, catastrophic failure.

A longitudinal study of cortical changes and their cognitive correlates in patients followed up after first-episode psychosis.

BACKGROUND: Loss of cortical volume in frontotemporal regions occurs in patients with first-episode psychosis (FEP) and longitudinal studies have reported progressive brain volume changes at different stages of the disease, even if cognitive deficits remain stable over time. We investigated cortical changes in patients over the 2 years following their FEP and their associations with clinical and cognitive measures. METHOD: Twenty-seven patients after their FEP (20 with schizophrenia, seven with schizo-affective disorder) and 25 healthy controls matched for age and gender participated in this study. Magnetic resonance imaging (MRI) was performed on a 1.5-T scanner both at baseline and after 2 years. Area and thickness of the cortex were measured using surface-based morphometry (SBM). Patients also underwent neuropsychological testing at these two time points. RESULTS: Progressive cortical thinning in the superior and inferior frontal and, to a lesser extent, superior temporal cortex was observed in patients. Cortical area remained constant. Cortical thinning was associated with duration of treatment at a trend level and was predicted by baseline measures of IQ and working memory. Cortical thinning occurred in the absence of clinical or cognitive deterioration. CONCLUSIONS: The clinical implications of these cortical changes remain uncertain, but patients with less cognitive reserve may be more vulnerable to developing cortical abnormalities when exposed to medication or other disease-related biological factors.

Renin-angiotensin system phenotyping as a guidance toward personalized medicine for ACE inhibitors: can the response to ACE inhibition be predicted on the basis of plasma renin or ACE?

PURPOSE & METHODS: Not all hypertensive patients respond well to ACE inhibition. Here we determined whether renin-angiotensin system (RAS) phenotyping, i.e., the measurement of renin or ACE, can predict the individual response to RAS blockade, either chronically (enalapril vs. enalapril + candesartan) or acutely (enalapril ± hydrochlorothiazide, HCT). RESULTS: Chronic enalapril + candesartan induced larger renin rises, but did not lower blood pressure (BP) more than enalapril. Similar observations were made for enalapril + HCT vs. enalapril when given acutely. Baseline renin predicted the peak changes in BP chronically, but not acutely. Baseline ACE levels had no predictive value. Yet, after acute drug intake, the degree of ACE inhibition, like Δrenin, did correlate with ΔBP. Only the relationship with Δrenin remained significant after chronic RAS blockade. Thus, a high degree of ACE inhibition and a steep renin rise associate with larger acute responses to enalapril. However, variation was large, ranging >50 mm Hg for a given degree of ACE inhibition or Δrenin. The same was true for the relationships between Δrenin and ΔBP, and between baseline renin and the maximum reduction in BP in the chronic study. CONCLUSIONS: Our data do not support that RAS phenotyping will help to predict the individual BP response to RAS blockade. Notably, these conclusions were reached in a carefully characterized, homogenous population, and when taking into account the known fluctuations in renin that relate to gender, age, ethnicity, salt intake and diuretic treatment, it seems unlikely that a cut-off renin level can be defined that has predictive value.

Reflection impulsivity and response inhibition in first-episode psychosis: relationship to cannabis use.

BACKGROUND: People with psychosis demonstrate impaired response inhibition on the Stop Signal Task (SST). It is less clear if this impairment extends to reflection impulsivity, a form of impulsivity that has been linked to substance use in non-psychotic samples. METHOD: We compared 49 patients with first-episode psychosis (FEP) and 30 healthy control participants on two forms of impulsivity measured using the Information Sampling Test (IST) and the SST, along with clinical and IQ assessments. We also compared those patients who used cannabis with those who had either given up or never used. RESULTS: Patients with FEP had significantly greater impairment in response inhibition but not in reflection impulsivity compared with healthy controls. By contrast, patients who reported current cannabis use demonstrated greater reflection impulsivity than those that had either given up or never used, whereas there were no differences in response inhibition. CONCLUSIONS: These data suggest that abnormal reflection impulsivity is associated with substance use in psychosis but not psychosis itself ; the opposite relationship may hold for response inhibition.

Inpatient treatment of functional motor symptoms: a long-term follow-up study.

Functional neurological disorders are common, disabling and often difficult to treat. There is little consensus on the best approach to management. Multidisciplinary inpatient approaches are employed in some centres for patients with severe refractory symptoms, but their efficacy and, in particular, long-term outcomes are uncertain. We conducted a study using questionnaires completed retrospectively by patients treated at a specialised multidisciplinary inpatient programme at the National Hospital for Neurology and Neurosurgery. Consecutive patients with functional motor symptoms admitted to this centre between 2006 and 2008 were invited to participate. Questionnaires were sent at least 2 years after discharge. We contacted 32 patients, and 26 responded. The majority had symptoms for at least 3 years prior to admission; 58 % of patients reported benefit from the programme on discharge. This self-reported benefit to symptoms and function was after a 2-year follow-up period in the majority of patients, but return to work or cessation of health-related financial benefits was uncommon even in those who improved. Seventy-four percent of those questioned stated they would recommend the programme to others with similar symptoms. Attribution of symptoms to stress or emotional state was correlated with favourable outcome. Our data suggest that multidisciplinary inpatient treatment for patients with refractory functional motor symptoms provides self-reported benefit in the long-term. Prospective analysis of such interventions and the determinants of benefit need assessment in order to improve the service and target treatment to patients most likely to benefit.

Abnormal negative feedback processing in first episode schizophrenia: evidence from an oculomotor rule switching task.

BACKGROUND: Previous studies have shown that patients with schizophrenia are impaired on executive tasks, where positive and negative feedbacks are used to update task rules or switch attention. However, research to date using saccadic tasks has not revealed clear deficits in task switching in these patients. The present study used an oculomotor 'rule switching' task to investigate the use of negative feedback when switching between task rules in people with schizophrenia. METHOD: A total of 50 patients with first episode schizophrenia and 25 healthy controls performed a task in which the association between a centrally presented visual cue and the direction of a saccade could change from trial to trial. Rule changes were heralded by an unexpected negative feedback, indicating that the cue-response mapping had reversed. RESULTS: Schizophrenia patients were found to make increased errors following a rule switch, but these were almost entirely the result of executing saccades away from the location at which the negative feedback had been presented on the preceding trial. This impairment in negative feedback processing was independent of IQ. CONCLUSIONS: The results not only confirm the existence of a basic deficit in stimulus-response rule switching in schizophrenia, but also suggest that this arises from aberrant processing of response outcomes, resulting in a failure to appropriately update rules. The findings are discussed in the context of neurological and pharmacological abnormalities in the conditions that may disrupt prediction error signalling in schizophrenia.

Dissociation of long-term verbal memory and fronto-executive impairment in first-episode psychosis.

BACKGROUND: Verbal memory is frequently and severely affected in schizophrenia and has been implicated as a mediator of poor clinical outcome. Whereas encoding deficits are well demonstrated, it is unclear whether retention is impaired. This distinction is important because accelerated forgetting implies impaired consolidation attributable to medial temporal lobe (MTL) dysfunction whereas impaired encoding and retrieval implicates involvement of prefrontal cortex. METHOD: We assessed a group of healthy volunteers (n=97) and pre-morbid IQ- and sex-matched first-episode psychosis patients (n=97), the majority of whom developed schizophrenia. We compared performance of verbal learning and recall with measures of visuospatial working memory, planning and attentional set-shifting, and also current IQ. RESULTS: All measures of performance, including verbal memory retention, a memory savings score that accounted for learning impairments, were significantly impaired in the schizophrenia group. The difference between groups for delayed recall remained even after the influence of learning and recall was accounted for. Factor analyses showed that, in patients, all variables except verbal memory retention loaded on a single factor, whereas in controls verbal memory and fronto-executive measures were separable. CONCLUSIONS: The results suggest that IQ, executive function and verbal learning deficits in schizophrenia may reflect a common abnormality of information processing in prefrontal cortex rather than specific impairments in different cognitive domains. Verbal memory retention impairments, however, may have a different aetiology.

Benefits of increasing the dose of influenza vaccine in residents of long-term care facilities: a randomized placebo-controlled trial.

Increased vaccine doses and mid-season boosting may increase the proportion of residents with protective immunity from influenza in long-term care facilities. In a multi-center study (1997-1998), 815 residents from 14 long-term care facilities were assigned at random to receive 15 or 30 microg of inactivated influenza vaccine, followed by a 15 microg booster vaccine or a placebo vaccine at Day 84. Seroresponses were re-analyzed by hemagglutination-inhibition (> or =4-fold titer increases, protective titer > or =40, geometric mean titers. Forty percent of the participants had pre-vaccination titers > or =40. At Day 25 after vaccination, this increased to 66.3% after a 15 microg dose versus 73.3% after a dose of 30 microg (P = 0.049). Participants receiving a 30 microg dose followed by a 15 microg booster showed more > or =4-fold titer increases at Day 109 (43.6% vs. 35.4%, P = 0.003) and protective titers > or =40 (74.2% vs. 64.6%, P = 0.041), compared to those receiving only a 15 microg dose. Differences were most apparent in participants with low pre-vaccination titers. Booster vaccination after an initial 15 microg dose of the vaccine did not increase the protective rate (61.9% vs. 63.9% after placebo). The number of participants needed to vaccinate to protect one additional resident by a dose of 15 microg was 4, by a dose of 30 microg 3, and 15 when using a 30 microg dose instead of 15 microg. Doubling the dose of influenza vaccine increased protection-related responses among residents of long-term care facilities, especially in those with low pre-vaccination titers.

Altered structural and mechanical properties in decellularized rabbit carotid arteries.

Recently, major achievements in creating decellularized whole tissue scaffolds have drawn considerable attention to decellularization as a promising approach for tissue engineering. Decellularized tissues are expected to have mechanical strength and structure similar to the native tissues from which they are derived. However, numerous studies have shown that mechanical properties change after decellularization. Often, tissue structure is observed by histology and electron microscopy, but the structural alterations that may have occurred are not always evident. Here, a variety of techniques were used to investigate changes in tissue structure and relate them to altered mechanical behavior in decellularized rabbit carotid arteries. Histology and scanning electron microscopy revealed that major extracellular matrix components were preserved and fibers appeared intact, although collagen appeared looser and less crimped after decellularization. Transmission electron microscopy confirmed the presence of proteoglycans (PG), but there was decreased PG density and increased spacing between collagen fibrils. Mechanical testing and opening angle measurements showed that decellularized arteries had significantly increased stiffness, decreased extensibility and decreased residual stress compared with native arteries. Small-angle light scattering revealed that fibers had increased mobility and that structural integrity was compromised in decellularized arteries. Taken together, these studies revealed structural alterations that could be related to changes in mechanical properties. Further studies are warranted to determine the specific effects of different decellularization methods on the structure and performance of decellularized arteries used as vascular grafts.

Impaired conscious and preserved unconscious inhibitory processing in recent onset schizophrenia.

BACKGROUND: Impairments in inhibitory function have been found in studies of cognition in schizophrenia. These have been linked to a failure to adequately maintain the task demands in working memory. As response inhibition is known to occur in both voluntary and involuntary processes, an important question is whether both aspects of response inhibition are specifically impaired in people with schizophrenia. METHOD: The subjects were 33 patients presenting with a first episode of psychosis (27 with schizophrenia and six with schizo-affective disorder) and 24 healthy controls. We administered two motor response tasks: voluntary response inhibition was indexed by the stop-signal task and involuntary response inhibition by the masked priming task. We also administered neuropsychological measures of IQ and executive function to explore their associations with response inhibition. RESULTS: Patients with schizophrenia compared to healthy controls showed significantly increased duration of the voluntary response inhibition process, as indexed by the stop-signal reaction time (SSRT). By contrast, there were no group differences on the pattern of priming on the masked priming task, indicative of intact involuntary response inhibition. Neuropsychological measures revealed that voluntary response inhibition is not necessarily dependent on working memory. CONCLUSIONS: These data provide evidence for a specific impairment of voluntary response inhibition in schizophrenia.