Assessing Adherence to Clozapine: Practical Considerations.

BACKGROUND: The clinical assessment of adherence to clozapine may prove difficult. METHOD: We studied the incidence of nonadherence (plasma clozapine <0.01 mg L -1 ) in samples submitted to a clozapine therapeutic drug monitoring (TDM) service, 1993-2017. RESULTS: Clozapine was not detected in 2865 samples from men (2214 patients, 1.1% of all samples from men) and 1068 samples from women (822 patients, 1.0% of all samples from women). Information on the prescribed dose was supplied for 1623 of these samples from men and 492 of these samples from women. Prescribed doses ranged up to 1200 mg d -1 , although most were in the range 100 to 600 mg d -1 . Norclozapine was detected in 260 (9.1%) and 67 (6.3%) of the samples from men and from women, respectively, that did not contain clozapine. While an assay was requested to confirm either a patient history of nonadherence, or to establish that clozapine had been cleared from the circulation after overdosage, for example, in at least 38 instances, in the vast majority of cases the absence of clozapine from the sample was unexpected. IMPLICATIONS: While adherence to clozapine may be good in general, tolerance to its potentially fatal cardiovascular effects is easily lost. Moreover, in treatment-resistant schizophrenia, the risk of self-harm increases if the drug is not taken regularly. In addition to presently available TDM services, the advent of a clozapine immunoassay for laboratory use should make it easy to institute at least monthly clozapine TDM at minimal extra cost.

The Use of Granulocyte Colony-Stimulating Factor in Clozapine Rechallenge: A Systematic Review.

PURPOSE/BACKGROUND: Clozapine is associated with hematological abnormalities, with neutropenia and agranulocytosis of most concern. Granulocyte colony-stimulating factor (G-CSF) has been used to support clozapine rechallenge after neutropenia with the aim of maintaining the neutrophil count. This study aims to explore the practice, use, safety, and efficacy of G-CSF in this context. METHODS/PROCEDURES: We conducted a systematic review to identify all studies investigating or describing G-CSF as a prophylaxis to enable continued clozapine treatment during a rechallenge. FINDINGS/RESULTS: We identified 32 reports of patients who received G-CSF either regularly (n = 23) or as required (n = 9) to support clozapine rechallenge after an episode of neutropenia necessitating discontinuation of clozapine. Seventy-five percent (n = 24) of published cases remained on clozapine with the use of continual prophylactic G-CSF or after single G-CSF administrations (n = 8). Seventy percent (n = 16) of patients in receipt of continual prophylactic G-CSF were successfully maintained on clozapine. However, 1 of the 3 episodes of rechallenge in those with a history of severe agranulocytosis (absolute neutrophil count <0.1 × 10/L) had a recurrence of agranulocytosis at week 9. IMPLICATIONS/CONCLUSIONS: Our findings suggest that G-CSF can sometimes be safely used to support the maintenance of normal neutrophil counts and clozapine use after neutropenia. Publication bias is an important limitation, however. Also, few reports clearly documented the presence or absence of an independent nonclozapine cause of the index neutropenia, which may have increased success rates. Furthermore, adverse events were not systematically recorded. Prospective studies are needed to determine safety because if agranulocytosis occurs on clozapine while supported by G-CSF, there is no obvious alternate rescue therapy to promote granulopoiesis. From the available data, it is not possible to recommend this course of action for someone with a true clozapine agranulocytosis.

Clozapine-Associated Agranulocytosis Treatment With Granulocyte Colony-Stimulating Factor/Granulocyte-Macrophage Colony-Stimulating Factor: A Systematic Review.

PURPOSE/BACKGROUND: Clozapine is associated with hematological abnormalities, notably neutropenia, which may progress to agranulocytosis. Granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) have been used to reduce the frequency and duration of clozapine-associated neutropenia. This review aims to explore the use, efficacy, and tolerability of these cytokines in the treatment of clozapine-associated agranulocytosis. METHODS/PROCEDURES: We conducted a systematic review of published interventional and observational studies, case series, and case reports where G-CSF/GM-CSF was used to treat clozapine-associated agranulocytosis. FINDINGS/RESULTS: We identified 29 reports (40 patients). The median duration of neutrophil recovery time after stopping clozapine and starting cytokine treatment was 7 days (range, 2-13 days) for those with agranulocytosis (absolute neutrophil count < 0.5 × 10 cells/L). Ninety-four percent (n = 29) had no serious adverse reactions, and no deaths occurred. IMPLICATIONS/CONCLUSIONS: Our findings indicate that G-CSF/GM-CSF use is well tolerated and suggest that G-CSF can sometimes be safely used to reduce the duration of neutropenia associated with clozapine use. However, the interpretation of this outcome is difficult, given the likely publication bias for positive outcomes in case reports.

An assessment of the variation in the concentration of acetylcysteine in infusions for the treatment of paracetamol overdose.

BACKGROUND: Intravenous acetylcysteine is the treatment of choice for paracetamol poisoning. A previous UK study in 2001 found that 39% of measured acetylcysteine infusion concentrations differed by >20% from anticipated concentrations. In 2012, the UK Commission on Human Medicines made recommendations for the management of paracetamol overdose, including provision of weight-based acetylcysteine dosing tables. The aim of this study was to assess variation in acetylcysteine concentrations in administered infusions following the introduction of this guidance. METHODS: A 6-month single-centre prospective study was undertaken at a UK teaching hospital. After preparation, 5-ml samples were taken from the first, second and third/any subsequent acetylcysteine infusions. Acetylcysteine was measured in diluted (1:50) samples by high-performance liquid chromatography. Comparisons between measured and expected concentrations based on prescribed weight-based dose and volume were made for each infusion. RESULTS: Ninety samples were collected. There was a variation of ≤10% in measured compared to expected concentration for 45 (50%) infusions, of 10-20% for 27 (30%) infusions, 20.1-50% for 14 (16%) infusions and >50% for four (4%) infusions. There was a median (interquartile range) variation in measured compared to expected concentration of -3.6 mg ml-1 (-6.7 to -2.3) for the first infusion, +0.2 mg ml-1 (-0.9 to +0.4) for the second infusion and -0.3 mg ml-1 (-0.6 to +0.2) for third and fourth infusions. CONCLUSION: There has been a moderate improvement in the variation in acetylcysteine dose administered by infusion. Further work is required to understand the continuing variation and consideration should be given to simplification of acetylcysteine regimes to decrease the risk of administration errors.

Measurement of Clozapine, Norclozapine, and Amisulpride in Plasma and in Oral Fluid Obtained Using 2 Different Sampling Systems.

BACKGROUND: There is a poor correlation between total concentrations of proton-accepting compounds (most basic drugs) in unstimulated oral fluid and in plasma. The aim of this study was to compare clozapine, norclozapine, and amisulpride concentrations in plasma and in oral fluid collected using commercially available collection devices [Thermo Fisher Scientific Oral-Eze and Greiner Bio-One (GBO)]. METHODS: Oral-Eze and GBO samples and plasma were collected in that order from patients prescribed clozapine. Analyte concentrations were measured by liquid chromatography-tandem mass spectrometry. RESULTS: There were 112 participants [96 men, aged (median, range) 47 (21-65) years and 16 women, aged 44 (21-65) years]: 74 participants provided 2 sets of samples and 7 provided 3 sets (overall 2 GBO samples not collected). Twenty-three patients were co-prescribed amisulpride, of whom 17 provided 2 sets of samples and 1 provided 3 sets. The median (range) oral fluid within the GBO samples was 52 (13%-86%). Nonadherence to clozapine was identified in all 3 samples in one instance. After correction for oral fluid content, analyte concentrations in the GBO and Oral-Eze samples were poorly correlated with plasma clozapine and norclozapine (R = 0.57-0.63) and plasma amisulpride (R = 0.65-0.72). Analyte concentrations in the 2 sets of oral fluid samples were likewise poorly correlated (R = 0.68-0.84). Mean (SD) plasma clozapine and norclozapine were 0.60 (0.46) and 0.25 (0.21) mg/L, respectively. Mean clozapine and norclozapine concentrations in the 2 sets of oral fluid samples were similar to those in plasma (0.9-1.8 times higher), that is, approximately 2- to 3-fold higher than those in unstimulated oral fluid. The mean (±SD) amisulpride concentrations (microgram per liter) in plasma (446 ± 297) and in the Oral-Eze samples (501 ± 461) were comparable and much higher than those in the GBO samples (233 ± 318). CONCLUSIONS: Oral fluid collected using either the GBO system or the Oral-Eze system cannot be used for quantitative clozapine and/or amisulpride therapeutic drug monitoring.

Women Administered Standard Dose Imatinib for Chronic Myeloid Leukemia Have Higher Dose-Adjusted Plasma Imatinib and Norimatinib Concentrations Than Men.

BACKGROUND: The standard dose of imatinib for the treatment of chronic-phase chronic myeloid leukemia (CML) is 400 mg·d. A predose plasma imatinib concentration of >1 mg·L is associated with improved clinical response. This study aimed to assess the plasma imatinib and norimatinib concentrations attained in patients with chronic myeloid leukemia administered standard doses of imatinib adjusted for dose, age, sex, body weight, and response. METHODS: We evaluated data from a cohort of patients treated between 2008 and 2014 with respect to dose, age, sex, body weight, and response. RESULTS: The study comprised 438 samples from 93 patients (54 male, 39 female). The median imatinib dose was 400 mg·d in men and in women. The plasma imatinib concentration ranged 0.1-5.0 mg·L and was below 1 mg·L in 20% and 16% of samples from men and women, respectively. The mean dose normalized plasma imatinib and norimatinib concentrations were significantly higher in women in comparison with men. This was partially related to body weight. Mixed effects ordinal logistic regression showed no evidence of an association between sex and plasma imatinib (P = 0.13). However, there was evidence of an association between sex and plasma norimatinib, with higher norimatinib concentrations more likely in women than in men (P = 0.02). CONCLUSIONS: Imatinib therapeutic drug monitoring only provides information on dosage adequacy and on short-term adherence; longer-term adherence cannot be assessed. However, this analysis revealed that approximately 1 in 5 samples had a plasma imatinib concentration <1 mg·L, which was suggestive of inadequate dosage and/or poor adherence and posed a risk of treatment failure. Higher imatinib exposure in women may be a factor in the increased rate of long-term, stable, deep molecular response (undetectable breakpoint cluster-Abelson (BCR-ABL) transcript levels with a PCR sensitivity of 4.5 log, MR4.5) reported in women.

Triazole antifungals used for prophylaxis and treatment of invasive fungal disease in adult haematology patients: Trough serum concentrations in relation to outcome.

Triazole antifungal drugs are widely used for the prophylaxis and treatment of invasive fungal disease (IFD). Efficacy may depend on attaining minimum effective plasma concentrations. The aim of this study was to ascertain the proportion of samples in which the recommended concentrations were achieved in patients given these drugs in relation to outcome. In-patients prescribed standard doses of fluconazole, itraconazole solution, posaconazole suspension, or oral voriconazole for at least one week were studied. Pre-dose serum triazole concentrations were measured using validated methods. There were 359 samples from 90 patients. The median (range) number of samples per patient was 3 (1-13), and the median (range) fluconazole, itraconazole, posaconazole (prophylaxis), posaconazole (treatment), and voriconazole serum concentrations were 5.64 (0.11-18), 0.57 (0-5.3), 0.31 (0.02-2.5), 0.65 (0.02-2.5), and 0.95 (0.10-5.4) mg/l, respectively. The number of samples in which the recommended pre-dose concentrations were achieved was 98 (54%), 9 (20%), 2 (18%), and 29 (49%) for itraconazole, posaconazole (>0.7 mg/l prophylaxis), posaconazole (treatment), and voriconazole, respectively. No significant differences were detected in the median triazole trough concentrations between patients with proven/probable IFD compared to those with no evidence of IFD. However, itraconazole was not detected in 10 samples (7 patients). The small number of patients who achieved the recommended trough posaconazole concentrations may explain the high rate of break-through IFD observed in patients prescribed this drug. Except for fluconazole, the number of patients prescribed standard doses of triazoles who achieved recommended trough triazole concentrations was low. The prospective use of serum triazole measurements assay may have improved outcomes with itraconazole, posaconazole, and with voriconazole.

Automated Analysis of Clozapine and Norclozapine in Human Plasma Using Novel Extraction Plate Technology and Flow-Injection Tandem Mass Spectrometry.

BACKGROUND: Analysis of plasma clozapine and N-desmethylclozapine (norclozapine) for therapeutic drug monitoring purposes is well established. To minimize analysis times and facilitate rapid reporting of results, we have fully automated sample preparation using novel AC Extraction Plates and a Tecan Freedom EVO 100 liquid handling platform, and minimized extract analysis times using flow-injection tandem mass spectrometry (FIA-MS/MS). METHODS: Analytes and deuterium-labeled internal standards were extracted from plasma (100 µL) at pH 10.6 and extracts analyzed directly using tandem mass spectrometry [20 µL injection, 0.7 mL/min methanol carrier flow, analysis time (injection-to-injection) approximately 60 seconds]. RESULTS: Validation data showed excellent intraplate and interplate accuracy (95%-104% nominal concentrations). Interbatch precision (% RSD) at the limit of quantitation (0.01 mg/L) was 3.5% and 5.5% for clozapine and norclozapine, respectively. Matrix effects were observed for both clozapine and norclozapine, but were compensated for by the internal standards. Overall process efficiency was 56%-70% and 66%-77% for clozapine and norclozapine, respectively. Mean relative process efficiency was 98% and 99% for clozapine and norclozapine, respectively. Comparison of results from patient samples (n = 81) analyzed using (1) manual liquid-liquid extraction with liquid chromatography-tandem mass spectrometry (LC-MS/MS) and (2) automated extraction with FIA-MS/MS gave y = 1.01x - 0.002, R(2) = 0.9943 and y = 1.01x + 0.009, R(2) = 0.9957 for clozapine and norclozapine, respectively. Bland-Altman plots revealed a [mean (95% limits of agreement) bias of 0.0074 (-0.04 to 0.06) mg/L and of 0.015 (-0.02 to 0.05) mg/L for clozapine and norclozapine, respectively]. CONCLUSIONS: FIA-MS/MS used with automated extraction offers a rapid, simple, cost-effective alternative to manual liquid-liquid extraction and conventional LC analysis for clozapine therapeutic drug monitoring.

Prevalence and Predictors of Clozapine-Associated Constipation: A Systematic Review and Meta-Analysis.

Constipation is a frequently overlooked side effect of clozapine treatment that can prove fatal. We conducted a systematic review and meta-analysis to estimate the prevalence and risk factors for clozapine-associated constipation. Two authors performed a systematic search of major electronic databases from January 1990 to March 2016 for articles reporting the prevalence of constipation in adults treated with clozapine. A random effects meta-analysis was conducted. A total of 32 studies were meta-analyzed, establishing a pooled prevalence of clozapine-associated constipation of 31.2% (95% CI: 25.6-37.4) (n = 2013). People taking clozapine were significantly more likely to be constipated versus other antipsychotics (OR 3.02 (CI: 1.91-4.77), p < 0.001, n = 11 studies). Meta-regression identified two significant study-level factors associated with constipation prevalence: significantly higher (p = 0.02) rates of constipation were observed for those treated in inpatient versus outpatient or mixed settings and for those studies in which constipation was a primary or secondary outcome measure (36.9%) compared to studies in which constipation was not a specified outcome measure (24.8%, p = 0.048). Clozapine-associated constipation is common and approximately three times more likely than with other antipsychotics. Screening and preventative strategies should be established and appropriate symptomatic treatment applied when required.

Tyrosine kinase inhibitors impair B-cell immune responses in CML through off-target inhibition of kinases important for cell signaling.

Tyrosine kinase inhibitors (TKIs) have significant off-target multikinase inhibitory effects. We aimed to study the impact of TKIs on the in vivo B-cell response to vaccination. Cellular and humoral responses to influenza and pneumococcal vaccines were evaluated in 51 chronic phase chronic myeloid leukemia (CML) patients on imatinib, or second-line dasatinib and nilotinib, and 24 controls. Following vaccination, CML patients on TKI had significant impairment of IgM humoral response to pneumococcus compared with controls (IgM titer 79.0 vs 200 U/mL, P = .0006), associated with significantly lower frequencies of peripheral blood IgM memory B cells. To elucidate whether CML itself or treatment with TKI was responsible for the impaired humoral response, we assessed memory B-cell subsets in paired samples collected before and after imatinib therapy. Treatment with imatinib was associated with significant reductions in IgM memory B cells. In vitro coincubation of B cells with plasma from CML patients on TKI or with imatinib, dasatinib, or nilotinib induced significant and dose-dependent inhibition of Bruton's tyrosine kinase and indirectly its downstream substrate, phospholipase-C-γ2, both important in B-cell signaling and survival. These data indicate that TKIs, through off-target inhibition of kinases important in B-cell signaling, reduce memory B-cell frequencies and induce significant impairment of B-cell responses in CML.

Sex differences in plasma clozapine and norclozapine concentrations in clinical practice and in relation to body mass index and plasma glucose concentrations: a retrospective survey.

BACKGROUND: Clozapine is widely prescribed and, although effective, can cause weight gain and dysglycemia. The dysmetabolic effects of clozapine are thought to be more prevalent in women with this gender on average attaining 17 % higher plasma clozapine concentrations than men. METHODS: We investigated the relationship between dose, body mass index (BMI), plasma glucose concentration, and plasma clozapine and N-desmethylclozapine (norclozapine) concentrations in 100 individuals with a severe enduring mental illness. RESULTS: Mean (10th/90th percentile) plasma clozapine concentrations were higher for women [0.49 (0.27-0.79) mg/L] compared with men [0.44 (0.26-0.70) mg/L] (F = 2.2; p = 0.035). There was no significant gender difference in the prescribed clozapine dose. BMI was significantly higher in women [mean (95 % CI) = 34.5 (26.0-45.3)] for females compared with 32.5 (25.2-41.0) for males. Overall, BMI increased by 0.7 kg/m(2) over a mean follow-up period of 210 days. A lower proportion, 41 % of women had a fasting blood glucose ≤6.0 mmol/L (<6.0 mmol/L is defined by the International Diabetes Federation as normal glucose handling), compared with 88 % of men (χ (2) = 18.6, p < 0.0001). CONCLUSIONS: We have shown that mean BMI and blood glucose concentrations are higher in women prescribed clozapine than in men. Women also tended to attain higher plasma clozapine concentrations than men. The higher BMI and blood glucose in women may relate to higher tissue exposure to clozapine, as a consequence of sex differences in drug metabolism.

Measurement of the direct oral anticoagulants apixaban, dabigatran, edoxaban, and rivaroxaban in human plasma using turbulent flow liquid chromatography with high-resolution mass spectrometry.

BACKGROUND: Direct oral anticoagulants (DOACs) are prescribed for systemic anticoagulation. Fixed doses are recommended, but dose individualization may be warranted. Functional coagulation assays may be available, but their use requires knowledge of the drug taken. To provide alternative methodology for guiding dosage, we have developed and validated a liquid chromatography-mass spectrometric assay for apixaban, dabigatran, edoxaban, and rivaroxaban at the concentrations attained during therapy. METHODS: Samples, calibrators, and internal quality controls (100 µL) were mixed with internal standard solution (50 µg/L both dabigatran-13C6 and rivaroxaban-13C6 in acetonitrile) and, after centrifugation (16,400g, 4 minutes), supernatant (100 µL) was injected onto a Cyclone-C18-P-XL TurboFlow column. Analytes were focused onto an Accucore PhenylHexyl (2.1 × 100 mm, 2.6 µm) analytical column and eluted using a methanol + acetonitrile (1 + 1):aqueous ammonium acetate (10 mmol/L) gradient. Data were acquired using high-resolution mass spectrometry in full-scan mode (100-2000 m/z) with data-dependent fragmentation to confirm peak identity. Calibration was linear (1-500 µg/L all analytes). RESULTS: Total analysis time was 6 minutes. Intra-assay imprecision (% RSD) at 1 µg/L was 2.6%, 4.2%, 17.3%, and 9.5% for apixaban, dabigatran, edoxaban, and rivaroxaban, respectively. Mean recovery was 96%-101%. No signal suppression or enhancement was observed. Apixaban, dabigatran, and rivaroxaban were stable over 3 freeze-thaw cycles, after storage at room temperature, and at 2-8°C for up to 2 weeks. Edoxaban was stable over 3 freeze-thaw cycles but showed a mean deterioration of 16% if stored at 2-8°C (2 weeks) and of 18% and 70% (1 day and 2 weeks, respectively) at room temperature. CONCLUSIONS: The method is suitable for high-throughput therapeutic drug monitoring of DOACs. The acquisition of full scan data allows for the retrospective identification of metabolites. The method can be used to identify a particular DOAC if information on the drug taken is lacking.

Clinical pharmacokinetics of tyrosine kinase inhibitors: implications for therapeutic drug monitoring.

The treatment of many malignancies has been improved in recent years by the introduction of molecular targeted therapies. These drugs interact preferentially with specific targets that are mutated and/or overexpressed in malignant cells. A group of such targets are the tyrosine kinases, against which a number of inhibitors (tyrosine kinase inhibitors, TKIs) have been developed. Imatinib, a TKI with targets that include the breakpoint cluster region-Abelson (bcr-abl) fusion protein kinase and mast/stem cell growth factor receptor kinase (c-Kit), was the first clinically successful drug of this type and revolutionized the treatment and prognosis of chronic myeloid leukemia and gastrointestinal stromal tumors. This success paved the way for the development of other TKIs for the treatment of a range of hematological malignancies and solid tumors. To date, 14 TKIs have been approved for clinical use and many more are under investigation. All these agents are given orally and are substrates of a range of drug transporters and metabolizing enzymes. In addition, some TKIs are capable of inhibiting their own transporters and metabolizing enzymes, making their disposition and metabolism at steady-state unpredictable. A given dose can therefore give rise to markedly different plasma concentrations in different patients, favoring the selection of resistant clones in the case of subtherapeutic exposure, and increasing the risk of toxicity if dosage is excessive. The aim of this review was to summarize current knowledge of the clinical pharmacokinetics and known adverse effects of the TKIs that are available for clinical use and to provide practical guidance on the implications of these data in patient management, in particular with respect to therapeutic drug monitoring.

Plasma, oral fluid, and whole-blood distribution of antipsychotics and metabolites in clinical samples.

BACKGROUND: Oral fluid provides a noninvasive method of sample collection. The aim of this study was to obtain oral fluid, plasma, and whole blood from patients prescribed amisulpride, aripiprazole, clozapine, quetiapine, risperidone, or sulpiride and to measure plasma:whole blood and plasma:oral fluid analyte distribution. METHODS: Matched oral fluid, plasma and whole-blood samples were analyzed by liquid chromatography-tandem mass spectrometry. RESULTS: There were 101 sets of samples from 90 (56 male, 34 female) patients (nine prescribed 2 antipsychotics, and one 3). There were ≤ 5 samples for aripiprazole, amisulpride, and sulpiride. There was a good relationship between the plasma and hemolyzed whole-blood concentrations (R > 0.95), with plasma:whole-blood ratios varying between 0.7 (amisulpride) and 1.8 (aripiprazole). Amisulpride plasma and oral fluid concentrations were similar, whereas aripiprazole and dehydroaripiprazole oral fluid concentrations were approximately 8% of those in the plasma, reflecting the weak and strong plasma protein binding of these compounds, respectively. For the other analytes, plasma concentrations were 2-4 times higher than oral fluid concentrations. In general, there was a poor relationship (R = 0.3-0.7) between the plasma and oral fluid concentrations, possibly due to intrapatient saliva pH variation during sample collection. CONCLUSIONS: This work shows that hemolyzed whole-blood samples can be used for therapeutic drug monitoring purposes for the analytes of interest, provided that the plasma:whole-blood ratio is taken into account when interpreting results. For aripiprazole and dehydroaripiprazole, measurements in oral fluid will probably not be feasible. However, the relationship between plasma and oral fluid concentration for amisulpride, clozapine (and norclozapine), quetiapine (and possibly quetiapine metabolites), and risperidone/9-hydroxyrisperidone shows potential for oral fluid analysis.

A novel approach to quantitative LC-MS/MS: therapeutic drug monitoring of clozapine and norclozapine using isotopic internal calibration.

Therapeutic drug monitoring (TDM) requires timely results in order to be clinically helpful. Such assays, when carried out using mass spectrometry-based methods, typically involve a batched sample approach with multipoint calibration. Isotopic internal calibration offers the possibility of open-access mass spectrometric analysis with consequent shortening of turnaround times. We measured plasma clozapine and N-desmethylclozapine (norclozapine) concentrations in (1) external quality assessment (EQA) samples (N = 22) and (2) patient samples (N = 100) using liquid chromatography-tandem mass spectrometry with isotopic internal calibration (ICAL-LC-MS/MS). Analyte concentrations were calculated from graphs of the response of three internal calibrators (clozapine-D4, norclozapine-D8, and clozapine-D8) against concentration. Precision (% RSD) and accuracy (% nominal concentrations) for the ICAL-LC-MS/MS method were <5 % and 104-112 %, respectively for both analytes. There was excellent agreement with consensus mean and with 'spiked' values on analysis of the EQA samples (R (2) = 0.98 and 0.97, respectively, inclusive of clozapine and norclozapine results). In the patient samples, comparison against traditionally calibrated HPLC-UV and LC-MS/MS methods showed excellent agreement (R (2) = 0.97 or better) with small albeit significant mean differences (<0.041 and <0.042 mg/L for clozapine and norclozapine, respectively). These differences probably reflect discrepancies in the in-house preparation of calibrators and/or interference in the UV method. Internal calibration offers a novel and attractive alternative to traditionally calibrated batch analysis in analytical toxicology. The method described has been validated for use in the high-throughput TDM of clozapine and norclozapine, and allows for (1) same-day reporting of results and (2) significant cost savings.

Risperidone and total 9-hydroxyrisperidone in relation to prescribed dose and other factors: data from a therapeutic drug monitoring service, 2002-2010.

BACKGROUND: Information on the plasma risperidone and total 9-hydroxyrisperidone concentrations ('total risperidone') attained in clinical practice is scant. The aim of this work was to gather such information to better inform the interpretation of results. METHOD: This involved the audit of plasma total risperidone data from a risperidone therapeutic drug monitoring service 2002-2010. RESULTS: There were 586 samples from 411 patients [289 (70%) males aged at the time of the first sample (median, range) 37 (7-83) years and 121 females aged 42 (10-91) years]. In patients aged 18 years and over, the mode of risperidone administration was oral: 242 samples (163 patients), risperidone long-acting injection (RLAI): 42 samples (39 patients), both oral and RLAI: 18 samples (12 patients), no information: 266 samples (211 patients). No risperidone/9-hydroxyrisperidone was detected in 10% of the samples, including 5 samples from patients prescribed RLAI. In the remainder, the mean (SD) total plasma total risperidone was all samples 35 (36), oral only 33 (29), RLAI only 23 (16), oral and RLAI 50 (21) µg/L. Overall, only 45% of the samples had plasma total risperidone within the range 20-59 mcg/L. Multiple linear regression analysis (95 samples) revealed that sex, smoking habit, and dose explained 21% of the variation in plasma total risperidone after oral dosage (dose alone only explained 11% of the variation). There was no discernable influence of age, body weight, and the plasma risperidone:total 9-hydroxyrisperidone ratio on plasma total risperidone. CONCLUSIONS: Risperidone therapeutic drug monitoring can help assess adherence and guide dosage even after RLAI.

Plasma concentrations of quetiapine, N-desalkylquetiapine, o-desalkylquetiapine, 7-hydroxyquetiapine, and quetiapine sulfoxide in relation to quetiapine dose, formulation, and other factors.

BACKGROUND: N-Desalkylquetiapine may be a pharmacologically active quetiapine metabolite. However, information on plasma concentrations of N-desalkylquetiapine and other quetiapine metabolites attained during quetiapine therapy is scant. The aim of this study was to investigate plasma concentrations of quetiapine, N-desalkylquetiapine, O-desalkylquetiapine, 7-hydroxyquetiapine, and quetiapine sulfoxide attained during therapy and analyze the data with respect to prescribed dose and other variables. METHOD: Quetiapine and its metabolites were measured in plasma samples submitted for quetiapine therapeutic drug monitoring (2009-2011). Concentration, metabolic ratio, and concentration corrected for dose (C/D) were investigated against quetiapine dose, age, sex, and formulation. Sample results were excluded if nonadherence with therapy was queried. RESULTS: There were 99 samples from 59 patients. N-Desalkylquetiapine plasma concentrations showed the strongest correlation with dose of all analytes, but O-desalkylquetiapine and quetiapine sulfoxide were strongly correlated to plasma quetiapine concentrations. There was no significant difference in C/D for any analyte between males and females and no correlation to age. Quetiapine and quetiapine sulfoxide C/D were significantly different (P < 0.01) between patients prescribed immediate- and extended-release formulations. Quetiapine, 7-hydroxyquetiapine and quetiapine sulfoxide C/D showed significant variation (P < 0.02) between those samples taken 10-14 hours postdose as compared with that of 16-24 hours postdose, but there was no significant effect as regards N-desalkylquetiapine. CONCLUSIONS: Plasma quetiapine, O-desalkylquetiapine, 7-hydroxyquetiapine, and quetiapine sulfoxide concentrations were significantly affected by formulation and/or time since last dose. Plasma N-desalkylquetiapine concentrations were not affected by either factor therefore may be a better marker for quetiapine exposure than plasma quetiapine concentrations.

Plasma amisulpride in relation to prescribed dose, clozapine augmentation, and other factors: data from a therapeutic drug monitoring service, 2002-2010.

OBJECTIVE: This study aimed to investigate the effect of dose and other factors on plasma amisulpride concentrations in clinical practice. METHOD: Amisulpride therapeutic drug monitoring data 2002-2010 have been studied. RESULTS: There were 296 samples (196 adult patients). Amisulpride was not detected in 10% of samples. In the remainder, the mean plasma amisulpride in relation to the prescribed dose (mg/day) was as follows: 100-200 (111 µg/L), 201-400 (254 µg/L), 400-800 (421 µg/L), and 800-1200 (494 µg/L). For prescribed doses up to 800 mg/day, only 51% of results were within 100-319 µg/L. There were no significant sex differences in mean plasma amisulpride or mean dose. The mean plasma amisulpride, but not the dose, was significantly higher in smokers. Linear regression analysis showed that dose explained only 42% of the variation in plasma amisulpride after log(10) transformation of both variables. There was no significant difference in the mean dose or mean plasma amisulpride in patients co-prescribed clozapine as compared with the remaining samples. CONCLUSION: In practice, dose is a poor predictor of plasma amisulpride concentration. Therapeutic drug monitoring may not only help assess adherence, but also guide dosage.

Measurement of quetiapine and four quetiapine metabolites in human plasma by LC-MS/MS.

There is interest in monitoring plasma concentrations of N-desalkylquetiapine in relation to antidepressant effect. A simple LC-MS/MS method for quetiapine and four metabolites in human plasma (50 µL) has been developed to measure concentrations of these compounds attained during therapy. Analytes and internal standard (quetiapine-d8) were extracted into butyl acetate-butanol (10:1, v/v) and a portion of the extract analysed by LC-MS/MS (100 × 2.1 mm i.d. Waters Spherisorb S5SCX; eluent: 50 mmol/L methanolic ammonium acetate, pH* 6.0; flow-rate 0.5 mL/min; positive ion APCI-SRM, two transitions per analyte). Assay calibration (human plasma calibrators) was linear across the ranges studied (quetiapine and N-desalkylquetiapine 5-800, quetiapine sulfoxide 100-15,000, others 2-100 µg/L). Assay validation was as per FDA guidelines. Quetiapine sulfone was found to be unstable and to degrade to quetiapine sulfoxide. In 47 plasma samples from patients prescribed quetiapine (prescribed dose 200-950 mg/day), the (median, range) concentrations found (µg/L) were: quetiapine 83 (7-748), N-desalkylquetiapine, 127 (7-329), O-desalkylquetiapine 12 (2-37), 7-hydroxyquetiapine 3 (<1-48), and quetiapine sulfoxide 3,379 (343-21,704). The analyte concentrations found were comparable to those reported by others except that the concentrations of the sulfoxide were markedly higher. The reason for this discrepancy in unclear.