Fabrication of a molecularly imprinted polymer-based electrochemical sensor for the selective assay of antipsychotic drug clozapine and performance comparison with LC-MS/MS.

Clozapine (CLO) is an atypical antipsychotic drug indicated for the treatment of schizophrenia. The treatment effectiveness of CLO is better than that of other atypical antipsychotics, and it has the advantage of being able to determine its effectiveness by measuring its concentration in the patient's blood. Thus, sensitive, selective, and accurate determination of CLO in blood is highly significant for treatment monitoring. This study describes the design and fabrication of a molecularly imprinted polymer (MIP)-based electrochemical sensor for CLO determination. This is the first MIP-based electrochemical application in the literature for CLO determination. Employing the thermal polymerization approach, the MIP was formed on the glassy carbon electrode (GCE) using CLO as the template, trans-3-(3-Pyridyl)acrylic acid (3,3-TA) as the functional monomer, and the support of zinc oxide nanoparticles (ZnO NPs). Elaborate characterizations in terms of surface morphology and electrochemistry were performed via scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods. An indirect approach was employed to determine CLO in standard solution, real human biological samples, and tablet formulation, using 5 × 10-3 M [Fe(CN)6]3-/4- solution as the redox probe. The limit of detection (LOD) values for the standard solution and serum sample were calculated as 2.9 × 10-11 M and 6.01 × 10-12 M, respectively. These values and recovery studies confirmed the sensor's sensitivity and feasibility. The measurements in the presence of similarly structured compounds (olanzapine and quetiapine fumarate) verified the sensor's superior selectivity. Moreover, the developed sensor's performance was compared and verified using an LC-MS/MS method using the student's t-test and F-test.

Long-term stability of five atypical antipsychotics (risperidone, olanzapine, paliperidone, clozapine, quetiapine) and the antidepressant mirtazapine in human serum assessed by a validated SPE LC-MS/MS method.

Long-term sample stability of five atypical antipsychoticdrugs risperidone, paliperidone, clozapine, quetiapine and olanzapine and the antidepressant drug mirtazapine in serum was studied by use of a newly developed and validated analytical method based on solid-phase extraction and liquid chromatography-tandem mass spectrometry. Ascorbic acid was used as an antioxidative agent to stabilize olanzapine during storage and sample preparation. We assessed analyte stability on long-term storage in serum samples at 25°C, 5°C, -20°C and -80°C, and during five freeze-thaw cycles. Analytes were stable for 23 days at room temperature except for olanzapine and mirtazapine (17 days). All analytes were stable for at least 30 days at 5°C. All analytes were stable for 270 days at -20°C, except for paliperidone and mirtazapine with 60 days and 180 days, respectively. All analytes were stable for 270 days at -80°C. Furthermore, all analytes were stable for five freeze-thaw cycles. We recommend storage at -80°C when samples drawn for analysis of antipsychotic drugs are stored for more than 60 days, whereas a temperature of -20°C is sufficient for storage less than 60 days.

Plasma Clozapine and N -Desmethylclozapine (Norclozapine) Concentrations and the Clozapine/Norclozapine Ratio : Effect of Dose, Sex, and Cigarette Smoking.

BACKGROUND: Smoking enhances plasma clozapine clearance, but the magnitude of the effect across the dose and age ranges is unclear. METHODS: We audited clozapine dose and predose plasma clozapine and N -desmethylclozapine (norclozapine) concentrations by sex and smoking habit in samples submitted for clozapine TDM, 1996-2017. RESULTS: There were 105,316/60,792 and 34,288/31,309 samples from male/female smokers/nonsmokers, respectively. There were distinct dose-median plasma concentration trajectories for male/female smokers/nonsmokers across the range <50 to >850 mg d -1 . For both sexes, the percentage difference in median plasma clozapine in nonsmokers versus smokers averaged 50% but was greatest for men (76%) and women (59%) in the 151 to 250 mg d -1 dose band. In men, the percentage difference declined steadily to 34% at doses of ≥850 mg d -1 . In women, the difference after falling initially remained relatively constant at 40% to 54%. The pattern in median plasma clozapine/norclozapine ratio by plasma clozapine concentration and dose groups was independent of sex and smoking habit, but increased with plasma clozapine concentration (higher ratio at higher concentrations) and also changed with dose. Median plasma clozapine concentration and median clozapine dose by sex and smoking habit were similar up to age 60 years. Proportional weight gain was similar over time in smokers and nonsmokers of either sex. IMPLICATIONS: These data explain the variations in the effect size of starting or stopping smoking on plasma clozapine concentration at constant dose reported in different studies. Changes in smoking habit in patients prescribed clozapine require prompt dose adjustment.

Clozapine levels and outcomes in Serbian patients with treatment-resistant psychotic disorders previously treated without measuring clozapine levels (CLOSER).

Clozapine remains the only pharmacological treatment option for treatment-resistant schizophrenia. Therapeutic drug monitoring (TDM) of clozapine is recommended, although evidence for the therapeutic range of 350-600 ng/ml is limited. In various countries including Serbia, TDM of clozapine is not routinely performed. This study evaluated the distribution of clozapine levels and their relationship with clinical outcomes in Serbian patients who had not undergone prior TDM. 140 Patients with treatment-resistant schizophrenia and schizo-affective disorder were enrolled. Clozapine levels were measured by dried blood spot (DBS) analysis. Side effects were evaluated by GASS-c, severity of symptoms and functional impairment with WHODAS, CGI-S and GAF. Of the patients, 51.2% had subtherapeutic levels, 24.8% were in the therapeutic window, and 24% had supratherapeutic levels. Clozapine levels showed no association with side effects and a weak positive association with symptom severity and functional impairment. No serious side effects were observed in patients with clozapine levels surpassing 1000 ng/ml (n = 8). Based on these findings, we propose that the upper limit of the therapeutic range should not be regarded as an absolute barrier, and guidelines should allow for a personalized approach when prescribing clozapine.

Detecting the therapeutic drugs in blood samples through PDMS-printed paper spray mass spectrometry.

In this paper, paper microfluidic channel fabricated by directly screen-printing of polydimethylsiloxane (PDMS) is proposed for paper spray mass spectrometry analysis of therapeutic drugs in the blood samples. Compared with traditional paper spray, PDMS-printed paper spray (PP-PS) allows fluid to flow to the tip of paper with less sample loss which significantly improved the signal intensity of target compounds in blood samples. As paper can reduce the matrix effect, PP-PS also has a greater advantage than electro-spray Ionization (ESI) when directly analyzing complex biological sample in terms of the detection efficiency. Linearity and limits of detection (LOD) were evaluated for five psychotropic drugs: olanzapine, quetiapine, 9-hydroxyrisperidone, clozapine, risperidone. As a result, PP-PS improved the signal intensity of the psychotropic drugs at a concentration of 250 ng/ml in blood samples by a factor of 2-5 times and lowered the relative standard deviation (RSD) by a factor of 2-5.6 times compared with traditional paper spray. And PP-PS also improved signal intensity by a factor of 9-33 times compared with ESI. Quantitative experiments of PP-PS mass spectrometry indicated that the linear range was 5-500 ng/ml and the LOD were improved by a factor of 5-71 times for all these drugs compared with traditional paper spray. In addition, PP-PS was applied to the home-made miniaturized mass spectrometer and the precursor ions of all five psychotropic drugs (250 ng/ml) in the mass spectrometry results were obtained as well. These could prove that PP-PS has the potential to analyze complex biological samples in application on the miniaturized mass spectrometer which can be used outside the laboratory.

Semi-physiological Pharmacokinetic Model of Clozapine and Norclozapine in Healthy, Non-smoking Volunteers: The Impact of Race and Genetics.

BACKGROUND AND OBJECTIVES: Clozapine is the medication of choice for treatment-resistant schizophrenia. However, it has a complex metabolism and unexplained interindividual variability. The current work aims to develop a pharmacokinetic model of clozapine and norclozapine in non-smokers and assess the impact of demographic and genetic predictors. METHODS: Healthy volunteers were recruited in a population pharmacokinetic study. Blood samples were collected at 30 min and 1, 2, 3, 5 and 8 h following a single flat dose of clozapine (12.5 mg). The clozapine and norclozapine concentrations were measured via high-performance liquid chromatography-ultraviolet method. A semi-physiological pharmacokinetic model of clozapine and norclozapine was developed using nonlinear mixed-effects modeling. Clinical and genetic predictors were evaluated, including CYP1A2 (rs762551) and ABCB1 (rs2032582), using restriction fragment length polymorphism. RESULTS: A total of 270 samples were collected from 33 participants. The data were best described using a two-compartment model for clozapine and a two-compartment model for norclozapine with first-order absorption and elimination and pre-systemic metabolism. The estimated (relative standard error) clearance of clozapine and norclozapine were 27 L h-1 (31.5 %) and 19.6 L h-1 (30%), respectively. Clozapine clearance was lower in sub-Saharan Africans (n = 4) and higher in Caucasians (n = 9) than Asians (n = 20). Participants with CYP1A2 (rs762551) (n = 18) and ABCB1 (rs2032582) (n = 12) mutant alleles had lower clozapine clearance in the univariate analysis. CONCLUSIONS: This is the first study to develop a semi-physiological pharmacokinetic model of clozapine and norclozapine accounting for the pre-systemic metabolism. Asians required lower doses of clozapine as compared with Caucasians, while clozapine pharmacokinetics in sub-Saharan Africans should be further investigated in larger trials.

Time for a change to clozapine haematological monitoring.

OBJECTIVES: This paper critiques the haematological monitoring guidelines for clozapine. It describes the history of clozapine, as well as the pathophysiology and epidemiology of clozapine-induced neutropenia (CIN) and agranulocytosis (CIA). The paper appraises the extant literature on mandatory clozapine haematological monitoring. CONCLUSION: Contemporary Australian protocols for clozapine haematological monitoring are not consistent with the current evidence base. CIN and CIA are rare occurrences, and the associated risk of death is low. Potential modifications to existing guidelines include changing neutrophil thresholds for patients with benign ethnic neutropenia and reducing the frequency or removing haematological monitoring after two years of clozapine treatment.

Exploring clozapine pharmacokinetics in Tunisian schizophrenic patients: A population-based modelling approach investigating the impact of genetic and non-genetic variables.

Clozapine is characterized by a large within- and between-patient variability in its pharmacokinetics, attributed to non-genetic and genetic factors. A cross-sectional analysis of clozapine trough concentration (Clz C0) issued from Tunisian schizophrenic patients was collected and analysed using a nonparametric modelling approach. We assessed the impact of demographic covariates (age, weight and sex), patient's habits (smoking status, alcohol and caffeine intake) and the genetic factors (CYP1A2*1C, CYP1A2*1F and CYP2C19*2 polymorphisms) on each pharmacokinetic parameter. An external validation of this pharmacokinetic model using an independent data set was performed. Fit goodness between observed- and individual-predicted data was evaluated using the mean prediction error (% MPE), the mean absolute prediction error (% MAPE) as a measure of bias, and the root mean squared error (% RMSE) as a measure of precision. Sixty-three CLz C0 values issued from 51 schizophrenic patients were assessed in this study and divided into building and validation groups. CYP1A2*1F polymorphism and smoking status were the only covariates significantly associated with clozapine clearance. Precision parameters were as follows: 1.02%, 0.95% and 22.4%, respectively, for % MPE, % MAPE and % RMSE. We developed and validated an accurate pharmacokinetic model able to predict Clz C0 in Tunisian schizophrenic patients using the two parameters CYP1A2*1F polymorphism and smoking.

Clozapine and COVID-19 Vaccination: Effects on blood levels and leukocytes. An observational cohort study.

OBJECTIVE: To investigate the safety of COVID-19 vaccination in patients on clozapine as regards plasma clozapine concentration and haematological parameters. METHODS: We conducted a multicentre observational cohort study from 22 February 2021 to 2 September 2021. Primary outcomes were clinically relevant increase in clozapine blood levels (>100 µg/L increase compared to baseline) and clozapine alert levels (>1000 µg/L). Secondary outcomes were granulocytopenia, leukocytopenia and lymphocytopenia. Outcomes were measured approximately 5 days after the first and (where applicable) second dose of COVID-19 vaccine. RESULTS: This study included 139 patients. Compared to baseline, clozapine blood levels increased significantly (ES = 0.28, p = 0.003) after the second vaccination. Clinically relevant increases in clozapine blood levels occurred in 20/92 patients (22%) and in 16/56 patients (29%) during the first and second phases, respectively. Clozapine alert levels developed in one patient (1%) following the first dose and in three patients (5%) after the second dose. In both phases, changes in white blood cells (WBC) were limited to mild granulocytopenia (3% and 5%), moderate granulocytopenia (1% and 0%) and leukocytopenia (2% and 3%) without cause for extra monitoring according to the guideline. CONCLUSION: In general, as regards WBC counts COVID-19 vaccination seems to be safe in patients with SMI. Changes in WBC had no clinical implications. Psychoeducation on the symptoms of clozapine intoxication is recommended, especially in patients with clozapine blood levels approaching the upper limit of the therapeutic range. Increase in the C-reactive protein (CRP) level can signal inflammation rapidly and help to prevent clozapine intoxication following vaccination.

Effect of Valproic Acid on the Metabolic Spectrum of Clozapine in Patients With Schizophrenia.

BACKGROUND: Valproic acid (VPA) is frequently used with clozapine (CLZ) as mood stabilizer and/or seizure prophylaxis. Valproic acid is known to reduce N-desmethylclozapine (N-DMC) but not CLZ levels. This leads to the hypothesis that VPA induces the CLZ metabolism via non-N-desmethylation pathways. Therefore, we aimed to investigate the effect of concurrent VPA use on the serum concentrations of a spectrum of CLZ metabolites in patients, adjusting for smoking. METHODS: In total, 288 patients with an overall number of 737 serum concentration measurements of CLZ and metabolites concurrently using VPA (cases, n = 22) or no interacting drugs (controls, n = 266) were included from a routine therapeutic drug monitoring service. Linear mixed model analyses were performed to compare the dose-adjusted concentrations (C/D) of CLZ, N-DMC, CLZ 5N/N+-glucuronides, and metabolite-to-parent ratios in cases versus controls. RESULTS: After adjusting for covariates, the N-DMC (-40%, P < 0.001) and N+-glucuronide C/Ds (-78%, P < 0.001) were reduced in cases versus controls, while the CLZ C/D was unchanged (P > 0.7). In contrast, the 5N-glucuronide C/D (+250%, P < 0.001) and 5N-glucuronide-to-CLZ ratios (+120%, P = 0.01) were increased in cases versus controls. CONCLUSIONS: Our findings show that complex changes in CLZ metabolism underly the pharmacokinetic interaction with VPA. The lower levels of N-DMC seem to be caused by VPA-mediated induction of CLZ 5N-glucuronide formation, subsequently leading to reduced substrate availability for N-desmethylation. Whether the changes in CLZ metabolism caused by VPA affects the clinical outcome warrants further investigation.

Pharmacogenetic excitation of the median raphe region affects social and depressive-like behavior and core body temperature in male mice.

AIMS: Median raphe region (MRR) is an important bottom-up regulatory center for various behaviors as well as vegetative functions, but detailed descriptions and links between the two are still largely unexplored. METHODS: Pharmacogenetics was used to study the role of MRR in social (sociability, social interaction, resident intruder test) and emotional behavior (forced swim test) parallel with some vegetative changes (biotelemetry: core body temperature). Additionally, to validate pharmacogenetics, the effect of clozapine-N-oxide (CNO), the ligand of the artificial receptor, was studied by measuring (i) serum and brainstem concentrations of CNO and clozapine; (ii) MRR stimulation induced neurotransmitter release in hippocampus; (iii) CNO induced changes in body temperature and locomotor activity. KEY FINDINGS: MRR stimulation decreased locomotion, increased friendly social behavior in the resident intruder test and enhanced depressive-like behavior. The latter was accompanied by diminished decrease in core body temperature. Thirty minutes after CNO injection clozapine was predominant in the brainstem. Nonetheless, peripheral CNO injection was able to induce glutamate release in the hippocampus. CNO had no immediate (<30 min) or chronic (repeated injections) effect on the body temperature or locomotion. SIGNIFICANCE: We confirmed the role of MRR in locomotion, social and depressive-like behavior. Most interestingly, only depressive-like behavior was accompanied by changed body temperature regulation, which was also observed in human depressive disorders previously. This indicates clinical relevance of our findings. Despite low penetration, CNO acts centrally, but does not influence the examined basic parameters, being suitable for repeated behavioral testing.

Absolute and Dose-Adjusted Serum Concentrations of Clozapine in Patients Switching vs. Maintaining Treatment: An Observational Study of 1979 Patients.

BACKGROUND: Clozapine is an effective drug for the management of schizophrenia that has not responded to other agents, but some patients experience insufficient or adverse effects and discontinue treatment. OBJECTIVE: We investigated a potential association between clozapine serum concentrations and switching to other antipsychotics in a large real-world patient population from a therapeutic drug monitoring service. METHODS: Absolute and dose-adjusted serum concentrations (concentration-to-dose ratios [C/D ratios]) of clozapine during dosing between 100 and 1000 mg/day were measured in 1979 Norwegian patients during the period 2005-2019. These variables were compared in patients switching to other antipsychotic drugs versus maintaining clozapine treatment using linear mixed models. Smoking habits were known for 49% of the patients. To prevent potential nonadherence affecting clozapine switching, only patients with serum concentrations above 50% of the lower reference range were included. RESULTS: In total, 190 patients (9.6%) switched from clozapine to another antipsychotic drug during the study period, whereas the remaining patients were not detected as switchers and were interpreted as maintaining treatment. Patients switching treatment had 23.5% lower absolute concentrations (954 vs. 1245 nmol/L; p < 0.001) and 15.7% lower daily doses (305 vs. 362 mg/day; p < 0.001) of clozapine than did nonswitchers, making the clozapine C/D ratio 9.7% lower in switchers than in nonswitchers after correcting for smoking habits (2.80 vs. 3.10 nmol/L/mg/day; p = 0.032). CONCLUSIONS: The present study suggests that decreased absolute and dose-adjusted serum concentrations of clozapine were associated with clozapine discontinuation. The significantly reduced clozapine concentrations regardless of prescribed dose in switchers versus nonswitchers may indicate a pharmacokinetic mechanism underlying the risk of clozapine discontinuation.

Infection is associated with elevated serum concentrations of antipsychotic drugs.

We aimed to investigate the effects of infection on serum concentrations of different antipsychotics in inpatients with respiratory tract infections treated with psychiatric drugs, including risperidone, clozapine, quetiapine, and aripiprazole. All patients underwent therapeutic drug monitoring (TDM) and routine blood tests during infection and noninfection periods. The Wilcoxon signed-rank test was used to analyze intra-individual differences in dose-corrected serum concentrations (C/D) levels in infection and noninfection periods. To study the effects of infection intensity on drug concentrations, white blood cells (WBCs) parameters and C/D levels were analyzed by Spearman's correlation analysis using all samples. The median C/D levels of risperidone (risperidone + 9-OH, n = 36) and clozapine (n = 42) were significantly higher (P < 0.001), whereas the median C/D levels of quetiapine (n = 21) and aripiprazole (n = 13) were slightly significantly higher (P < 0.01) in infection than in noninfection period. A significant positive association between C/D levels and WBC parameters was observed for risperidone, clozapine, and quetiapine. These results indicated reduced clearance of all drugs evaluated, especially clozapine and risperidone, due to infection. Therefore, during infection in patients receiving risperidone, clozapine, quetiapine, or aripiprazole, TDM should be performed to minimize the possible adverse effects associated with elevated drug concentrations.

Clinical and genetic influencing factors on clozapine pharmacokinetics in Tunisian schizophrenic patients.

Clozapine (Clz) is an atypical antipsychotic, which its pharmacokinetics can be influenced by several factors. The CYP1A2 and CYP2C19, major enzymes implicated in Clz metabolism, present an interethnic variation on their activity caused by single nucleotide polymorphisms (SNPs). The present study investigated the influence of genetic and nongenetic factors on Clz pharmacokinetics in a southern Mediterranean population. We included adult Tunisian schizophrenic patients having received Clz and undergone a therapeutic drug monitoring (TDM) of Clz by morning C0 monitoring. The genomic DNA was extracted using a salting-out procedure. CYP1A2*1F (rs762551;-163C>A), CYP1A2*1C (rs2069514;-3860 G>A) and CYP 2C19*2 (rs4244285; 681G>A) was analyzed using PCR-RFLP. Fifty-one patients were enrolled in the study. The mutant allele (CYP1A2*1F) was the most frequently detected (58.8%). For CYP1A2*1F, Clz dose-normalized (C0/D ratio) was as high as 1.28 ± 0.37 in CC versus 0.67 ± 0.32 ng mL-1 per mg day-1 in AA group (p < 0.001). The influence of genetic (CYP1A2*1F, CYP1A2*1C and CYP2C19*2) and nongenetic parameters (age, weight, gender, tobacco, coffee, and alcohol consumption) on the variation of the Clz C0/D ratio was investigated. Only the CYP1A2*1 F polymorphism correlates significantly with the Clz C0/D variation and could explain 24% of its variability. Our data support a critical role of the CYP1A2 -163C>A on the variation of Clz exposure in Tunisian schizophrenic patients. Considering its narrow therapeutic range, CYP1A2 genotyping combined with TDM of Clz may improve efficacy and safety of this drug. Further studies are needed to investigate this issue.

Point-of-care measurement of clozapine concentration using a finger-stick blood sample.

BACKGROUND: The use of clozapine demands regular monitoring of clozapine plasma concentrations and of white blood cell parameters. The delay between sending blood samples for analysis and receiving the results hinders clinical care. Point-of-care testing (POCT) can provide drug assay results within a few minutes. AIM: This study aimed to investigate the utility of a novel point-of-care device that can measure clozapine concentrations using capillary blood samples collected via a finger stick. METHOD: During a five-week period starting in June 2019 eligible patients were asked to provide a finger-stick capillary sample in addition to their usual venous blood sample. Samples were analysed by the novel point-of-care device and by the standard laboratory method. Capillary blood samples were tested by the MyCare™ Insite POCT analyser, and a quantitative measurement of clozapine concentration was provided within six minutes. RESULTS: A total of 309 patients agreed to measurements by the two methods. Analysis revealed clozapine concentrations in venous blood as determined by the laboratory method ranged from 20 to 1310 ng/mL and by POCT from 7 to 1425 ng/mL. There was a strong positive correlation (R = 0.89) between the results from the venous and the capillary sample methods. The slope of the association between standard assay and MyCare™ Insite was 1.0 with an intercept of -21 ng/mL, indicating minimal bias. CONCLUSION: Clozapine concentrations can be accurately measured at the point of care using capillary blood samples collected via a finger stick. This approach may be more acceptable than venous sampling to patients and, with almost instant results available, more useful to clinicians.

Development of a simultaneous analytical method for clozapine and its metabolites in human plasma using liquid chromatography/electrospray ionization tandem mass spectrometry with linear range adjusted by in-source collision-induced dissociation.

Clozapine (CLZ) is a key drug in treatment-resistant schizophrenia. Therapeutic drug monitoring (TDM) of CLZ and its metabolites, N-desmethylclozapine and clozapine N-oxide, is required to monitor and manage the risks of side effects. Although quantification methods for TDM have been developed for CLZ and its metabolites, they were not sufficiently accurate for the quantification of CLZ owing to the upper limits of the calibration curves. An analytical method using high-performance liquid chromatography/electrospray ionization tandem mass spectrometry was developed and validated for the simultaneous measurement of CLZ and its metabolites in human plasma. To expand the concentration range of the calibration curves, we used a linear range shift technique using in-source collision-induced dissociation (CID). Using our approach, the linearity and quantitative range were improved compared to those reported by previous studies, and were sufficient for TDM in clinical practice. The intra- and inter-assay accuracy was 84.6%-114.8%, and the intra- and inter-assay precisions were ≤9.1% and ≤9.9%, respectively. Moreover, all samples from patients with treatment-resistant schizophrenia were successfully quantified. Therefore, our novel analytical method using in-source CID had the appropriate performance to measure the plasma concentrations of CLZ and its metabolites for TDM in clinical practice.

High-Dose Fluvoxamine Augmentation to Clozapine in Treatment-Resistant Psychosis.

BACKGROUND: Although clozapine is the gold standard for treatment-resistant schizophrenia, more than 30% of patients remain unresponsive to clozapine monotherapy and may benefit from augmentation strategies. Fluvoxamine augmentation of clozapine may be beneficial in treatment resistance because of pharmacokinetic interactions, allowing for lower clozapine dosages with higher clozapine serum levels and an increased clozapine-to-norclozapine ratio, which can modify adverse effects. An augmentation strategy using higher fluvoxamine doses may also improve persistent negative, anxiety, and obsessive-compulsive symptoms through fluvoxamine's serotonergic activity. METHODS: Through chart review, we identified 4 cases of patients with treatment-resistant psychosis who underwent high-dose fluvoxamine augmentation of clozapine to target residual negative symptoms, refractory psychosis, anxiety, and obsessive-compulsive symptoms. FINDINGS: This augmentation strategy continued in 2 patients after discharge who showed clinical improvement without significant adverse effects. Two patients experienced adverse effects that led to the fluvoxamine discontinuation. Despite the fact that fluvoxamine augmentation led to symptom improvement in only 2 patients, all patients achieved high serum clozapine levels. Hematologic parameters were monitored in all patients, and no abnormalities were observed. No severe adverse effects of clozapine were experienced. CONCLUSIONS: Although high variability of responses and adverse effects were observed during fluvoxamine augmentation to clozapine, this strategy was successful in increasing clozapine serum levels. Through fluvoxamine's serotonergic effects, this strategy may confer benefit to residual negative, obsessive, and anxiety symptoms. Limitations of this case series include the retrospective nature, absence of controls, diversity of diagnoses, multiple interventions in each patient, and lack of masked raters.