Prolonged sedation and slowly decreasing clozapine serum concentrations after an overdose

Second to none: rationale, timing, and clinical management of clozapine use in schizophrenia

Despite its enduring relevance as the single most effective and important evidence-based treatment for schizophrenia, underutilization of clozapine remains considerable. To a substantial degree, this is attributable to a reluctance of psychiatrists to offer clozapine due to its relatively large side-effect burden and the complexity of its use. This underscores the necessity for continued education regarding both the vital nature and the intricacies of clozapine treatment. This narrative review summarizes all clinically relevant areas of evidence, which support clozapine's wide-ranging superior efficacy - for treatment-resistant schizophrenia (TRS) and beyond - and make its safe use eminently feasible. Converging evidence indicates that TRS constitutes a distinct albeit heterogeneous subgroup of schizophrenias primarily responsive to clozapine. Most importantly, the predominantly early onset of treatment resistance and the considerable decline in response rates associated with its delayed initiation make clozapine an essential treatment option throughout the course of illness, beginning with the first psychotic episode. To maximize patients' benefits, systematic early recognition efforts based on stringent use of TRS criteria, a timely offer of clozapine, thorough side-effect screening and management as well as consistent use of therapeutic drug monitoring and established augmentation strategies for suboptimal responders are crucial. To minimize permanent all-cause discontinuation, re-challenges after neutropenia or myocarditis should be considered. Owing to clozapine's unique efficacy, comorbid conditions including substance use and most somatic disorders should not dissuade but rather encourage clinicians to consider clozapine. Moreover, treatment decisions need to be informed by the late onset of clozapine's full effects, which for reduced suicidality and mortality rates may not even be readily apparent. Overall, the singular extent of its efficacy combined with the high level of patient satisfaction continues to distinguish clozapine from all other available antipsychotics.

Successful Treatment of an Acute High-Dose Clozapine Poisoning without Detoxication

Patient: Male, 28-year-old

Final Diagnosis: Clozapine poisoning

Symptoms: Drowsiness • hyperventilation • impaired consciousness • respiratory insufficiency • tachycadia

Medication: —

Clinical Procedure: —

Specialty: Critical Care Medicine • Psychiatry

Abnormal olanzapine toxicokinetic profiles--population pharmacokinetic analysis

CONTEXT

Olanzapine is widely used in the treatment of schizophrenia and it is becoming more frequently responsible for overdoses. Standard pharmacokinetic models do not fit to the toxic concentration data.

OBJECTIVE

The aim of present study is to investigate the reasons for an abnormal olanzapine plasma concentration time curve in the range of toxic concentrations. Two hypotheses were verified: entering the enterohepatic cycle, and drug deposition and its desorption from activated charcoal used for gastrointestinal decontamination.

MATERIALS AND METHODS

One-hundred thirty-five plasma concentration data from 21 patients hospitalized for acute olanzapine poisoning were analyzed with the use of the population pharmacokinetic approach. A non-linear mixed-effects modeling approach with Monolix 4.3.1 was employed.

RESULTS

A model assuming gallbladder emptying at irregular intervals was developed. Also, a model that describes desorption of olanzapine from the charcoal surface, in which the dose is divided into two absorbed fractions, was constructed. The analysis has found gastrointestinal decontamination and previous olanzapine treatment, as the significant covariates for toxicokinetic parameters of olanzapine.

CONCLUSION

Our study provides interesting models for investigation of toxic concentration of olanzapine, which may also be used as the basis for further model development for other drugs as well. The investigated population was not large enough to reliably confirm any of the proposed models. It would be well worth continuing this study with more substantial data. Also, any additional information about olanzapine metabolite concentration could be vital.

Teaching Application of Clinical Pharmacology Skills Using Unusual Observations from Clozapine Overdoses

Massive drug overdoses provide a unique opportunity to observe human pharmacokinetic data not otherwise ethically available. They can also provide practical examples for teaching thoughtful application of the principles of clinical pharmacology. Following a case of clozapine overdose in which onset of toxicity was delayed by 72 hours, a probable explanation was found in an exploration of three cases with unusual concentration-time profiles and revealed unexpected implications for the management of clozapine overdoses. The authors systematically addressed the possible mechanisms proposed in the literature for an unusual plateau in concentrations observed in three clozapine overdoses. The effects that the most commonly suggested explanations (i.e., delayed absorption and saturated or impaired metabolism) would have on both clozapine and norclozapine concentrations were then modeled using the data available from those three cases to provide an objective illustration for comparison. This exercise was then used as a teaching seminar, leading students through the steps required to reach a logical explanation for the observed delayed toxicity and to consider the implications for therapy. Delayed absorption best predicted the sustained serum clozapine and norclozapine concentrations observed in three cases, and modeling suggests that much of the drug remains in the gut, available for absorption for days following an overdose. As a seminar, the exercise provides students with a practical example of the value of systematically ruling out possible explanations by considering what effects various pharmacokinetic alterations would have on observed data. Absorption following massive clozapine overdose appears fundamentally different from that with conventional dosing. This suggests a potential for delayed or prolonged toxicity, extending well beyond the time frame predicted by its half-life, unless aggressive and sustained efforts are applied to remove clozapine from the gut. Data from drug overdoses provide opportunities to explore unusual aspects of pharmacokinetics, better understand future overdoses of the same agent, and present excellent material for teaching. A seminar illustrating the role that thoughtful application of pharmacologic principles had in addressing this case is now used to introduce the clinical aspects of pharmacology to students at our institutions.

Increased clozapine plasma concentrations and side effects induced by smoking cessation in 2 CYP1A2 genotyped patients

Clozapine, an atypical antipsychotic, depends mainly on cytochrome P4501A2 (CYP1A2) for its metabolic clearance. CYP1A2 is inducible by smoking, and lower plasma concentrations of clozapine are measured in smokers than in nonsmokers. Case reports have been published on the effects of discontinuing smoking in patients receiving clozapine, which might lead to elevated plasma concentrations and severe side effects. We present 2 cases on the consequences of smoking cessation in patients receiving this drug. In the first patient, smoking cessation resulted, within 2 weeks, in severe sedation and fatigue, with an approximately 3-fold increase of plasma clozapine concentrations. In the second patient, a very high plasma concentration of clozapine (3004 ng/mL) was measured 6 days following a 16-day stay in a general hospital, during which smoking was prohibited. In the latter patient, the replacement of omeprazole, a strong CYP1A2 inducer, by pantoprazole, a weaker CYP1A2 inducer, could have contributed, in addition to smoking cessation, to the observed strong increase of plasma clozapine concentrations. Genotyping of the 2 patients revealed that they were carriers of the AA genotype for the -164C>A polymorphism (CYP1A2*1F) in intron 1 of CYP1A2 gene, which has previously been shown to confer a high inducibility of CYP1A2 by smoking. Thus, at the initiation of clozapine treatment, smoking patients should be informed that, if they decide to stop smoking, they are encouraged to do so but must inform their prescriber beforehand. Also, because of the increased use of no-smoking policies in many hospitals, studies examining the consequences of such policies on the pharmacokinetics/pharmacodynamics of drugs metabolized by CYP1A2, taking into account different CYP1A2 genotypes, are needed.

Suspected clozapine poisoning in the UK/Eire, 1992–2003

OBJECTIVE

Toxicological analyses are often performed to investigate suspected poisoning, but the interpretation of results may not be straightforward. We studied suspected poisoning cases 1992-2003 where blood clozapine and N-desmethylclozapine (norclozapine) were measured in order to assess the relationship of these parameters to outcome.

METHODS

Samples were referred from clinicians, pathologists/coroners, or via the Clozaril Patient Monitoring Service (CPMS, Novartis). Information was gathered from clinical, post-mortem, or coroners' reports.

RESULTS

There were seven fatal [five male, two female; median (range) age 28 (24-41) year] and five non-fatal [four male, one female; median age 35 (26-41) year] clozapine overdoses. The median post-mortem blood clozapine and norclozapine concentrations were 8.2 (3.7-12) and 1.9 (1.4-2.4)mg/L, respectively [median clozapine:norclozapine ratio 4.4 (2.9-5.1)]. The median plasma clozapine and norclozapine concentrations (first or only sample) were 3.9 (1.7-7.0) and 0.40 (0.30-0.70)mg/L, respectively [median clozapine:norclozapine ratio 7.6 (5.3-18)] in the remainder. These overdoses were in patients who were poorly or non-adherent to clozapine, or who had taken tablets prescribed for someone else. In 54 further people who died whilst receiving clozapine [38 male, 16 female; median age 41 (22-70) year], the median post-mortem blood clozapine and norclozapine concentrations were 1.9 (0-7.7, n = 43) and 1.4 (0-6.0, n = 39)mg/L, respectively [median clozapine:norclozapine ratio 1.5 (0.4-7.6, n = 38)]. The median post-mortem increase in blood clozapine and norclozapine as compared to the most recent ante-mortem measurement was 489 (98-5,350)% and 371 (139-831)%, respectively [median sample time before death 14 (0-30, n = 21) days].

CONCLUSION

Clozapine poisoning cannot be diagnosed on the basis of blood clozapine and norclozapine concentrations alone. The analysis of ante-mortem blood specimens collected originally for white cell count monitoring and the blood clozapine:norclozapine ratio may provide additional interpretative information.

Delayed recovery associated with persistent serum concentrations after clozapine overdose

Experience with managing overdoses of the atypical antipsychotic agent, clozapine, has been limited. A 20-year-old woman, who presented 6 h after ingesting 3500 mg of clozapine, had an unexpectedly prolonged duration of tachycardia and somnolence. Successful recovery followed management with supportive measures for several days in the intensive care unit. However, the duration of symptoms greatly exceeded that predicted by the published 12-h half-life of clozapine and was associated with an unexplained persistence of serum clozapine concentrations. Recovery with normalization of autonomic function occurred only after serum clozapine began to decline again after a 4-day plateau, as revealed by serum monitoring. Similar observations have been reported in two other cases. In overdose, clozapine may not behave as predicted by its published pharmacokinetics. Persistent serum drug concentrations may prolong the period of intensive care, suggesting that aggressive measures to remove clozapine from the gut at the time of overdose may be warranted.

Clozapine intoxication in a dog

Intoxication with clozapine in a dog, suspected from history and clinical signs at presentation, was confirmed by demonstration of decreasing serum levels of this drug. Clozapine is a tricyclic dibenzodiazepine used for treatment of human schizophrenia, and clinical signs of intoxication in humans include tachycardia, seizures, muscle fasciculations, agitation, and sialorrhea. This dog showed ptyalism, hyperthermia, tachycardia, and was easily excited by tactile or auditory stimulation. The calculated peak concentration of clozapine in this dog was approximately 6,000 ng/mL, and the elimination half-life (t(1/2)) was 5 hours. Charcoal administration and supportive care led to a successful outcome in this patient.

The pharmacology and toxicology of atypical antipsychotic agents

Recently, atypical antipsychotic agents have largely replaced traditional agents as first-line drugs for the treatment of schizophrenia. It is likely that atypical agents will soon account for the majority of poisonings from antipsychotic agents that present to health care facilities in the US. This article reviews the pharmacodynamics, pharmacokinetics, and toxicology of atypical antipsychotic drugs, chiefly clozapine, risperidone, olanzapine, and quetiapine. A descriptive summary of the human overdose experience with these agents is provided. Adverse effect and drug interaction data are reviewed. Based on the available pharmacodynamic, pharmacokinetic, and human overdose data, recommendations on management are provided.