Plasma clozapine, norclozapine, and the clozapine:norclozapine ratio in relation to prescribed dose and other factors: data from a therapeutic drug monitoring service, 1993-2007

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.

Reintroduction of Clozapine After Perforation of the Large Intestine—A Case Report and Review of the Literature

OBJECTIVE

To report on a patient who was successfully rechallenged with clozapine after perforation of the large intestine and pulmonary embolism postoperatively, and provide a literature review on clozapine rechallenge.

CASE SUMMARY

A 46-year-old Japanese man with treatment-resistant schizophrenia developed constipation and slight abdominal discomfort while taking clozapine 275 mg/day. He developed appendicitis, leading to perforation of the large intestine. During the postsurgery period, a partial embolism of the pulmonary artery was revealed. The patient's constipation was relieved when clozapine was discontinued, but other antipsychotics failed to control his delusions well. After thorough discussion, it was decided to rechallenge with clozapine. The low dose of clozapine 200 mg/day was tolerable for his delusion, and his constipation was managed with laxatives and exercises until 8 months after the accident.

DISCUSSION

Clozapine is a gold standard medication in treatment-resistant schizophrenia but is associated with various adverse effects, some of which are life-threatening. Reintroduction of clozapine after severe adverse drug effects when other medications are not effective almost always poses a clinical dilemma for mental health professionals. A PubMed search (to January 25, 2013) using the key words clozapine and rechallenge found 50 articles. There were only sporadic positive case reports regarding the rechallenge after clozapine-related serious gastrointestinal problems.

CONCLUSIONS

From the currently available evidence, most psychiatrists appear to avoid reintroduction of clozapine. However, the evidence is too weak to draw a definitive conclusion about reintroduction of this drug. Reintroduction of clozapine after initial adverse effects in patients with treatment-resistant schizophrenia may warrant case-by-case judgment, but needs to be further investigated.

Plasma clozapine and norclozapine in relation to prescribed dose and other factors in patients aged <18 years: data from a therapeutic drug monitoring service, 1994-2010

AIM

Clozapine is used in children and adolescents to treat early onset schizophrenia, but data on efficacy and on the plasma clozapine concentrations attained are limited.

METHODS

We studied data from a clozapine therapeutic drug monitoring (TDM) service, patients in the UK and Eire aged <18 years, 1994-2010. Multiple linear regression analysis was performed to investigate the relationship between plasma clozapine concentration and dose, age, sex, body weight, plasma clozapine:norclozapine ratio (clozapine metabolic ratio (MR)) and smoking habit.

RESULTS

There were 1408 samples from 454 patients, 267 (59%) males aged at time of first sample (median = 17; range = 8-17 years) and 187 (41%) females aged 16 (10-17) years. The plasma clozapine concentration was <0.35 mg L(-1) in 36%, and ≥0.60 mg L(-1) in 31% of samples (6.4% samples ≥1.0 mg L(-1) ). Although plasma clozapine was broadly related to prescribed dose, there was much variation: 10% of samples had plasma clozapine >0.60 mg L(-1) at prescribed clozapine doses of 50-150 mg d(-1) (66% <0.35 mg L(-1) ), while 12% of samples had plasma clozapine <0.35 mg L(-1) at doses ≥650 mg d(-1) (62% >0.6 mg L(-1) ). The covariates studied in the 16-17-year-olds had proportionately similar influences to those observed in adults. Together they explained 48% of the variance observed in plasma clozapine, with dose, smoking habit, MR and sex being major influences. In the younger patients, there were very few smokers, and the influence of sex did not reach statistical significance.

CONCLUSIONS

As in adults, clozapine TDM may help in assessing adherence and in dose adjustment, for example if smoking habit changes.

Clozapine and therapeutic drug monitoring: is there sufficient evidence for an upper threshold?

RATIONALE

Clozapine levels are advocated in the monitoring of patients on this drug and have now been used for a number of years. A safety-related threshold has also been proposed, as well as therapeutic lower and upper thresholds. While there has been reasonable consensus regarding a lower therapeutic threshold, this is not the case for the upper thresholds.

OBJECTIVES

Our aim was to review available evidence related to upper thresholds.

METHODS

We carried out an electronic search of different databases and a manual search of articles between 1960 and 2011, cross-referencing the following terms with clozapine-interactions, monitoring, pharmacokinetics, plasma levels, serum levels, and toxicity.

RESULTS

Sixty-nine articles met our search criteria and these could be divided into reviews (11), studies (24), and case reports (35). Study quality was evaluated, and none met criteria for a prospective, randomized controlled trial specifically addressing higher plasma levels, e.g., >500 ng/ml. Case reports emphasize in particular the impact of interactions, e.g., antidepressants and smoking. There is clear evidence indicating a dose-related increased risk of seizures, at least to 500-600 mg/day, but a lack of data to suggest such a relationship between plasma levels, dose, and side effects linked to safety, e.g., seizures, myocarditis, and agranulocytosis. The very limited evidence addressing an upper threshold related to clinical response suggests a "ceiling effect" in the range of 600-838 ng/ml.

CONCLUSIONS

It appears that the current safety-related threshold is not supported by evidence. There may be an upper threshold for clinical response, beyond which chance of response falls off, although further studies are warranted.

Clinical pharmacology of dopamine-modulating agents in Tourette's syndrome

Forty years of research and clinical practice have proved dopamine (DA) receptor antagonists to be effective agents in the treatment of Tourette's syndrome (TS), allowing a significant tic reduction of about 70%. Their main effect seems to be mediated by the blockade of the striatal DA-D2 receptors. Various typical and atypical agents are available and there is still discord between experts about which of them should be considered as first choice. In addition, there are suggestions to use DA receptor agonists such as pergolide or non-DA-modulating agents. The present chapter is focusing on the clinical pharmacology of DA-modulating agents in the treatment of TS. The introduction outlines their clinical relevance and touches on the hypotheses of the role of DA in the pathophysiology of TS. Subsequently, general information about the mechanisms of action and adverse effects are provided. The central part of the chapter forms a systematic review of all DA-modulating agents used in the treatment of TS, including an overview of studies on their effectiveness, and a critical discussion of their specific adverse effects. The present chapter closes with a summary of the body of evidence and a description of the resulting recommendations for the pharmacological treatment of TS.

Glucuronidation of the second-generation antipsychotic clozapine and its active metabolite N-desmethylclozapine. Potential importance of the UGT1A1 A(TA)₇TAA and UGT1A4 L48V polymorphisms

INTRODUCTION

Clozapine (CLZ) is an FDA approved second-generation antipsychotic for refractory schizophrenia, and glucuronidation is an important pathway in its metabolism. The aim of this study was to fully characterize the CLZ glucuronidation pathway and examine whether polymorphisms in active glucuronidating enzymes could contribute to variability in CLZ metabolism.

METHODS

Cell lines overexpressing wild-type or variant uridine diphosphate-glucuronosyltransferase (UGT) enzymes were used to determine which UGTs show activity against CLZ and its major active metabolite N-desmethylclozapine (dmCLZ). Human liver microsomes (HLM) were used to compare hepatic glucuronidation activity against the UGT genotype.

RESULTS

Several UGTs including 1A1 and 1A4 were active against CLZ; only UGT1A4 showed activity against dmCLZ. UGT1A1 showed a 2.1-fold (P <0.0001) higher V(max)/K(M) for formation of the CLZ-N⁺-glucuronide than UGT1A4; UGT1A4 was the only UGT for which CLZ-5-N-glucuronide kinetics could be determined. The UGT1A4(24Pro/48Val) variant showed a 5.2-, 2.0-, and 3.4-fold (P < 0.0001 for all) higher V(max)/K(M) for the formation of CLZ-5-N-glucuronide, CLZ-N⁺-glucuronide, and dmCLZ-5-N-glucuronide, respectively, as compared with that of wild-type UGT1A4(24Pro/48Leu). There was a 37% (P< 0.05) decrease in the rate of CLZ-N⁺-glucuronide formation in HLM with the UGT1A1 (*28/*28)/UGT1A4 (*1/*1) genotype, and a 2.2- and 1.8-fold (P < 0.05 for both) increase in the formation of CLZ-5-N-glucuronide and CLZ-N⁺-glucuronide in UGT1A1 (*1/*1)/UGT1A4 (*3/*3) HLM compared with UGT1A1 (*1/*1)/UGT1A4 (*1/*1) HLM. The UGT1A1*28 allele was a significant (P = 0.045) predictor of CLZ-N⁺-glucuronide formation; the UGT1A4*3 allele was a significant (P < 0.0001) predictor of CLZ-5-N-glucuronide and dmCLZ-glucuronide formation.

CONCLUSION

These data suggest that the UGT1A1*28 and UGT1A4*3 alleles contribute significantly to the interindividual variability in CLZ and dmCLZ metabolism.

Clinician hesitation prior to clozapine initiation: is it justifiable?

Clozapine has been endorsed by national clinical guidelines for 10 years and yet underutilisation and delay to initiation remain rife. Although there will be good clinical reasons for clozapine not being initiated for some patients, it is hypothesised here that for others, clinicians' attitudes and preferences are the most likely predictive factors.

Therapeutic drug monitoring of common antipsychotics

The aim of this review is to provide information for interpreting outcome results from monitoring of antipsychotics in biological samples. A brief overview of the working mechanisms, pharmacological effects, drug interactions, and analytical methods of classical and atypical antipsychotics is given. Nineteen antipsychotics were selected based on their importance in the worldwide market as follows: amisulpride, aripiprazole, asenapine, bromperidol, clozapine, flupenthixol, haloperidol, iloperidone, lurasidone, olanzapine, paliperidone, perphenazine, pimozide, pipamperone, quetiapine, risperidone, sertindole, sulpiride, and zuclopenthixol. A straightforward relationship between administered dose, plasma or serum concentration, clinical outcome, or adverse effects is often lacking. Nowadays, focus lies on therapeutic drug monitoring and individualized therapy to find adequate treatment, to explain treatment failure or nonresponse, and to check patient compliance. However, extensive research in this field is still mandatory.

Rapid clozapine dose titration and concomitant sodium valproate increase the risk of myocarditis with clozapine: a case-control study

BACKGROUND

Despite the implementation of cardiac monitoring guidelines, clozapine-induced myocarditis continues to cause deaths in Australia, and the risk is a barrier to prescription of this effective drug for the treatment of schizophrenia. This study was designed to identify clinical and phenotypic risk factors for clozapine-induced myocarditis.

METHOD

Possible cases of clozapine related myocarditis occurring between June 1993 and November 2009 and a comparative group of controls taking clozapine for at least 45days without cardiac disease were documented from the patients' medical records.

RESULTS

105 cases, with time to onset of 10-33days, and 296 controls were included in the study. In multivariate analysis, the risk of myocarditis increased by 26% for each additional 250mg of clozapine administered in the first nine days of clozapine titration (odds ratio 1.26; 95% confidence interval 1.02-1.55; p=0.03) and concomitant sodium valproate more than doubled the risk (2.59; 1.51-4.42; 0.001). Further, each successive decade in age was associated with a 31% increase in risk (1.31; 1.07-1.60; 0.009). Nevertheless, 33 cases received less than 920mg of clozapine during the first nine days of dose titration, did not take sodium valproate and were aged less than 40years; and nine control patients received sodium valproate and more than 920mg of clozapine in the first nine days without developing myocarditis.

CONCLUSIONS

Clozapine should be initiated by slow dose titration and sodium valproate is best avoided, if clinically feasible, during this period. All patients commencing clozapine should be monitored for myocarditis up to Day 28.

Population pharmacokinetics of clozapine and its primary metabolite norclozapine in Chinese patients with schizophrenia

AIM

To develop a combined population pharmacokinetic model (PPK) to assess the magnitude and variability of exposure to both clozapine and its primary metabolite norclozapine in Chinese patients with refractory schizophrenia via sparse sampling with a focus on the effects of covariates on the pharmacokinetic parameters.

METHODS

Relevant patient concentration data (eg, demographic data, medication history, dosage regimen, time of last dose, sampling time, concentrations of clozapine and norclozapine, etc) were collected using a standardized data collection form. The demographic characteristics of the patients, including sex, age, weight, body surface area, smoking status, and information on concomitant medications as well as biochemical and hematological test results were recorded. Persons who had smoked 5 or more cigarettes per day within the last week were defined as smokers. The concentrations of clozapine and norclozapine were measured using a HPLC system equipped with a UV detector. PPK analysis was performed using NONMEM. Age, weight, sex, and smoking status were evaluated as main covariates. The model was internally validated using normalized prediction distribution errors.

RESULTS

A total of 809 clozapine concentration data sets and 808 norclozapine concentration data sets from 162 inpatients (74 males, 88 females) at multiple mental health sites in China were included. The one-compartment pharmacokinetic model with mixture error could best describe the concentration-time profiles of clozapine and norclozapine. The population-predicted clearance of clozapine and norclozapine in female nonsmokers were 21.9 and 32.7 L/h, respectively. The population-predicted volumes of distribution for clozapine and norclozapine were 526 and 624 L, respectively. Smoking was significantly associated with increases in the clearance (clozapine by 45%; norclozapine by 54.3%). The clearance was significantly greater in males than in females (clozapine by 20.8%; norclozapine by 24.2%). The clearance of clozapine and norclozapine did not differ significantly between Chinese patients and American patients.

CONCLUSION

Smoking and male were significantly associated with a lower exposure to clozapine and norclozapine due to higher clearance. This model can be used in individualized drug dosing and therapeutic drug monitoring.

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.

A review of the use of clozapine levels to guide treatment and determine cause of death

OBJECTIVE

To review the literature to examine the use of clozapine levels to (i) guide therapy and prevent toxicity in clinical care and (ii) determine cause of death in post-mortem examination of patients who were treated with clozapine.

METHODS

MEDLINE was searched in December 2010 using the following keywords: 'clozapine levels', 'clozapine and toxicity', 'clozapine and death', 'clozapine and mortality' and 'post-mortem redistribution'. Data was also collected from the 2010 MIMS Annual.

RESULTS

The literature reported significant variation in clozapine levels attained with any given dose, and considerable variability in the clinical response achieved at any given clozapine level. The lowest effective clozapine levels ranged from 250 to 550 µg/L, while the recommended upper limit to prevent toxicity varied from 600 to 2000 µg/L. There was minimal correlation between clozapine levels and side effects, with the exception of sedation, hypotension and seizure activity. The risk of seizures increased with plasma clozapine levels greater than 600 µg/L or rapid upward titration. In addition to prescribed dose, there are many factors that influence plasma clozapine levels. After death, the process of post-mortem drug redistribution resulted in 3.00 to 4.89 times increases in clozapine levels in central blood vessels and 1.5 fold increases in peripheral vessels compared to ante-mortem levels.

CONCLUSIONS

The exact range of clozapine levels that corresponds to toxicity remains unclear. However, levels between 350 µg/L and 1000 µg/L achieved with gradual upward titration are more likely to be effective and less likely to cause toxicity. Ongoing clozapine level monitoring is indicated, especially when (i) prescribing higher doses (> 600 mg/day) of clozapine, (ii) there has been a change in a patient's concomitant pharmacotherapy or cigarette use and (iii) there has been a suboptimal response to treatment. The use of post-mortem clozapine levels to determine clozapine toxicity as a cause of death is unreliable.

Microdialysis evaluation of clozapine and N-desmethylclozapine pharmacokinetics in rat brain

A significant barrier to realization of the full potential of clozapine as a therapeutic agent in the treatment of schizophrenia is the substantial interpatient variability that exists along the therapeutic continuum of no response-efficacious response-adverse response. Genetic polymorphisms that manifest as highly variable pharmacodynamic and pharmacokinetic measures are its expected causes. To support investigations that seek to understand these causes, the plasma and central nervous system pharmacokinetics of clozapine were determined in rats, the latter using microdialysis sampling. Results obtained with clozapine and N-desmethylclozapine, a pharmacologically active human metabolite that was administered to a separate group of animals, support a conclusion of net carrier-mediated efflux of both compounds across the blood-brain barrier. These results are supported by the replication of published findings regarding the passive transport and net efflux transport of two model compounds, escitalopram and risperidone, respectively. The results obtained with clozapine and N-desmethylclozapine are considered a first step in the development of preclinical pharmacokinetic-pharmacodynamic models that will support deeper mechanistic studies of clozapine in in vivo pharmacology, as well as the development of translational models that augment pharmacogenetic investigations that seek to improve the safety and efficacy of clozapine therapeutic intervention in the treatment of schizophrenia.

Plasma clozapine and norclozapine in relation to prescribed dose and other factors in patients aged 65 years and over: data from a therapeutic drug monitoring service, 1996-2010

OBJECTIVE

To investigate the effect of dose and other factors on plasma clozapine concentrations in patients aged 65 years and over.

METHOD

Audit of clozapine therapeutic drug monitoring data, 1996-2010.

RESULTS

There were 1930 samples [778 patients, 363 men aged (median, range) 67 (65-100) years and 415 women aged 68 (65-90) years]. There was no significant difference in the mean plasma clozapine concentration between men (0.56 mg/l) and women (0.58 mg/l), although the mean dose was higher in men (323 mg/d) than women (264 mg/d). The higher proportion of men (46%) compared with women (37%) smokers could explain this finding. Overall, 32% of samples had plasma clozapine below, and 37% above, a target range of 0.35-0.60 mg/l. Overall, the median dose decreased from 300 (65-70 years) to 200 mg/d (age 85 years and over). However, prescription of >350 mg/d was associated with a 50% likelihood that the plasma clozapine would exceed 0.60 mg/l. For a subgroup of 196 patients (114 men, 82 women), mean plasma clozapine was significantly higher after age 65 despite significantly lower dosage.

CONCLUSION

Clozapine dosage in elderly patients should be reviewed regularly to minimise the risk of adverse effects.

Age and sex impact clozapine plasma concentrations in inpatients and outpatients with schizophrenia

BACKGROUND

Although clozapine is primarily used in a younger to mid-life population of patients with psychosis, there are limited data on the clinical pharmacology of clozapine later in life. The objective of this study was to assess the magnitude and variability of plasma concentrations of clozapine and norclozapine across the lifespan in a real-world clinical setting.

DESIGN

A population pharmacokinetic study using nonlinear mixed effect modeling (NONMEM). Age, sex, height, weight, and dosage formulation were covariates.

SETTING

Inpatients and outpatients at the Centre for Addiction and Mental Health, Toronto, from 2001 to 2007.

PARTICIPANTS

Patients ranging in ages from 11 to 79 with schizophrenia spectrum disorders and prescribed clozapine (Clozaril).

MEASUREMENTS

A total of 1142 plasma clozapine and norclozapine concentrations (2,284 concentration measurements) from 391 patients with schizophrenia spectrum disorder.

RESULTS

A one-compartment model with first-order absorption and elimination best described the data. The population predicted clearance of clozapine for females was 27.1 L/h (SE 11.1%) and 36.7 L/h (SE 9.7%) for males. For norclozapine, clearance in females was 48.6 L/h (SE 10.8%) and 63.1 L/h (SE 9.3%) in males. The only covariates with a significant effect on clearance were age and sex: clearance for both parent and metabolite decreased exponentially with age at least 39 years.

CONCLUSIONS

Decreased clearance of clozapine and norclozapine with age results in increased blood concentrations and, hence, the potential for adverse drug reactions. These findings have particular clinical relevance for the dosing and safety monitoring of clozapine in older adults, highlighting a need for increased vigilance.

Clozapine--a dangerous drug in a clozapine-naïve subject

Clozapine is a uniquely effective antipsychotic, but is very toxic in clozapine-naïve subjects. A 34-year-old male patient in a mental health facility, who was not prescribed clozapine, took 350 mg clozapine obtained from another patient at night. He was found dead the next morning. The presence of cardiomegaly related to obesity may have increased the risk of suffering an acute cardiac event after ingestion of clozapine. The medication prescribed to the patient was not thought to have contributed to the fatal outcome. Post mortem femoral blood clozapine and norclozapine concentrations were 0.48 and 0.20mg/L, respectively. By way of comparison, audit of 104,127 plasma samples (26,796 patients) assayed for therapeutic drug monitoring purposes 1993-2007, showed plasma clozapine 0.35 mg/L or more in 57.5% samples (8.4% 1mg/L or more). Those involved in the investigation of clozapine-associated deaths need to be aware that that death in an adult may occur after a single 'therapeutic' dose. A diagnosis of fatal clozapine poisoning cannot be made solely on the basis of a post mortem blood clozapine measurement.

The clozapine metabolite N-desmethylclozapine displays variable activity in diverse functional assays at human dopamine D₂ and serotonin 5-HT₁A receptors

N-desmethylclozapine (NDMC or norclozapine) is the major active metabolite of the antipsychotic clozapine in humans. The activity of NDMC differs from clozapine at a number of neurotransmitter receptors, probably influencing the pharmacological effects of clozapine treatment. Here, we tested the properties of NDMC in comparison with clozapine at recombinant human dopamine D(2) and serotonin 5-HT(1A) receptors, using a panel of functional assays implicating diverse signalling pathways. At dopamine D(2) receptors, NDMC as well as clozapine did not display agonist activity in measures of G protein activation by [(35)S]GTPγS binding and in the sensitive Extracellular Signal-Regulated Kinase 1/2 (ERK1/2) phosphorylation assay. In contrast, there were weak partial agonist actions of NDMC (but not of clozapine) for dopamine D(2)-dependent activation of Ca(2+) liberation via coexpressed chimeric Gα(q/o) proteins and for G protein-coupled inward rectifier potassium channel (GIRK) current induction in Xenopus oocytes. Intriguingly, GIRK currents induced by NDMC via dopamine D(2) receptors showed a rapid and transient time course, strikingly different from currents recorded with other receptor agonists. At serotonin 5-HT(1A) receptors, NDMC was a more efficacious partial agonist than clozapine for [(35)S]GTPγS binding, ERK1/2 phosphorylation and GIRK activation. Respective low and moderate partial agonist properties of NDMC at dopamine D(2) and serotonin 5-HT(1A) receptors thus differentiate the metabolite from its parent drug and may contribute to the overall effects of clozapine pharmacotherapy.

Gastrointestinal hypomotility: an under-recognised life-threatening adverse effect of clozapine

AIM

To highlight some problems that may occur when investigating clozapine-associated deaths including (i) that death may be related to gastrointestinal hypomotility and (ii) that post-mortem blood clozapine and norclozapine concentrations may not reflect ante-mortem concentrations.

CASE REPORTS

A 41-year-old male died 40 min after admission to hospital as a result of aspiration complicating severe, clozapine-induced constipation. At post-mortem the small bowel was dilated and contained bloodstained mucus, particularly within the jejunum. The large bowel was considerably dilated and contained large quantities of foul-smelling, bloodstained fluid and a small amount of stool. Its lining was focally congested, but there was no other obvious abnormality. Analysis of serum obtained on admission revealed clozapine and norclozapine concentrations of 0.56 and 0.43 mg/L, respectively, whereas post-mortem femoral whole blood obtained <34 h after death showed clozapine and norclozapine concentrations of 3.73 and 1.75 mg/L, respectively. In 6 out of a further 12 clozapine-associated deaths investigated 2002-9 there were reports of gastrointestinal tract problems of varying severity.

CONCLUSIONS

Severe constipation or paralytic ileus in clozapine-treated patients may lead to intestinal necrosis and/or perforation, or pulmonary aspiration. In some such cases the immediate cause of death may be obvious, but in others only careful assessment of the clinical course of the terminal illness may reveal gastrointestinal hypomotility as a likely underlying cause of death.