High-dose clozapine intoxication

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

Delayed complications after severe clozapine intoxication: a case report. The pharmacokinetic profile of clozapine and it's important role in the course of symptoms

Clozapine intoxications have a varied clinical presentation and may have severe complications. Management and treatment guidelines rarely highlight the risks of delayed clinical presentations. We present the case of a 50-year-old man showing severe complications 15 hours after intoxication with 4200 mg clozapine. Treatment consisted of strict monitoring, including vital support and regular clozapine blood levels. Clinical presentations may be delayed up to 5 days after intoxication, for which strict monitoring of clinical symptoms and vital functions during this period is of major importance. We discuss the clinical course of clozapine intoxication, the value of sampling clozapine blood levels and provide an overview of the current treatment guidelines, which we suggest to update to include the management of delayed complications.

A review of the clinical utility of serum clozapine and norclozapine levels

Treatment refractory schizophrenia is a serious issue affecting at least 30% of all patients with schizophrenia despite the continued emergence of new agents aimed at treating this disease. Clozapine therapy remains the most efficacious treatment for patients with schizophrenia who have failed two prior antipsychotics or those deemed an imminent harm to themselves or others. Because data are lacking on how to proceed if a patient should prove nonresponsive to clozapine therapy, the utmost care should be taken to ensure the optimization of clozapine. Therapeutic drug monitoring (TDM) is used with many other psychoactive agents to ensure the optimal therapeutic efficacy while minimizing adverse effects. The unique pharmacology of clozapine and the inter- and intraindividual variations in its pharmacokinetics make it a difficult agent with which to use TDM. The consensus is that 350 ng/mL is the lower threshold of therapeutic efficacy to define an adequate trial of clozapine. As of this writing, no clearly defined threshold exists for the upper limit of therapeutic efficacy or toxicity. TDM of clozapine can be useful in the following circumstances: when a clozapine-induced central nervous system toxicity is suspected, a medication that can inhibit or induce the metabolism of clozapine is being added or withdrawn, a change in smoking status has occurred, concerns for medication nonadherence are present, or decompensation while on a previously effective clozapine dosage is observed. The psychiatric pharmacist may play a crucial role in the interpretation and effective utilization of serum clozapine and norclozapine levels. This review will examine the current evidence for the clinical utility of monitoring serum levels of clozapine and its metabolites.

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.

Overdose of atypical antipsychotics: clinical presentation, mechanisms of toxicity and management

Historically, treatment for schizophrenia focused on sedation. The advent of the typical antipsychotics resulted in treatment aimed specifically at the underlying disease, but these agents were associated with numerous adverse effects, and were not particularly effective at treatment of the negative symptoms of schizophrenia. As a result, numerous atypical agents have been developed over the past 2 decades, including several agents within the past 5 years. Overdose of antipsychotics remains quite common in Western society. In 2010, poison control centres in the US received nearly 43,000 calls related to atypical antipsychotics alone. Due to underreporting, the true incidence of overdose with atypical antipsychotics is likely much greater. Following overdose of an atypical antipsychotic, the clinical effects observed, such as CNS depression, tachycardia and orthostasis are largely predictable based on the unique receptor binding profile of the agent. This article, which focuses on the atypical antipsychotics commonly used in the treatment of schizophrenia, discusses the features commonly encountered in overdose. Specifically, agents that result in QT prolongation and the corresponding potential for torsades de pointes, as well as unique features encountered with the various medications are discussed. The diagnosis of this overdose is largely based on history. Routine use of drug screens is unlikely to be beneficial. The primary goal of management is aggressive supportive care. Patients with significant CNS depression with associated loss of airway reflexes and respiratory failure need advanced airway management. Hypotension should be treated first with intravenous fluids, with the use of direct acting vasopressors reserved for persistent hypotension. Benzodiazepines should be used for seizures, with barbiturates used for refractory seizures. Intravenous magnesium can be administered for patients with a corrected QT interval exceeding 500 milliseconds.

Development of a method of clozapine dosage by selective electrode to the iodides

Clozapine (Leponex(®)), the main neuroleptic indicated in the treatment of resistant schizophrenia, requires therapeutic monitoring because of its side effects and the individual variability in metabolism. In addition, several cases of intoxication by this drug were described in the literature. In this work, we studied the indirect dosage of clozapine by selective electrode to the iodides for the optimization of an analytical protocol allowing therapeutic monitoring and the diagnosis of intoxication and/or overdose. Our results showed that the developed method is linear between 0.05 and 12.5 µg/mL (r = 0.980), with a limit of detection of 0.645.10(-3) µg/mL. It presents good precision (coefficient of variation less than 4%) and accuracy (coefficient less than 10%) for all the studied concentrations. With a domain of linearity covering a wide margin of concentrations, this method can be applicable to the dosage of clozapine in tablets and in different biological matrices, such as plasma, urines, and postmortem samples.

Optimizing clozapine treatment

OBJECTIVE

Clozapine treatment remains the gold standard for treatment-resistant schizophrenia, but treatment with clozapine is associated with several side-effects that complicate the use of the drug. This clinical overview aims to provide psychiatrists with knowledge about how to optimize clozapine treatment. Relevant strategies for reducing side-effects and increasing the likelihood of response are discussed.

METHOD

Studies of clozapine available in MEDLINE were reviewed.

RESULTS

A slow up-titration of clozapine is recommended in order to reach the optimal dosage of clozapine and diminish the risk of dose-dependent side-effects. Particularly, in case of partial response or non-response, the use of therapeutic drug monitoring of clozapine is recommended. Plasma levels above the therapeutic threshold of 350-420 ng/ml are necessary to determine non-response to clozapine. To ease the burden of dose-dependent side-effects, dose reduction of clozapine should be tried and combination with another antipsychotic drug may facilitate further dose reduction. For most side-effects, counteracting medication exists. Augmentation with lamotrigine, antipsychotics, or electroconvulsive therapy may be beneficial in case of partial response to clozapine.

CONCLUSION

Treatment with clozapine should be optimized in order to increase the rate of response and to minimize side-effects, thus diminishing the risk of discontinuation and psychotic relapse.

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.

Serum clozapine levels: a review of their clinical utility

Therapeutic drug monitoring (TDM) is frequently utilized in the treatment of psychiatric conditions, but its clinical application concerning the use of clozapine is unclear. We present three case reports of patients taking clozapine, review the relevant literature, and propose guidelines to aid the clinical use of TDM of clozapine. Due to its complex metabolism, there are significant inter- and intra-individual variations in clozapine serum levels, for a given dose. However, the range of serum levels that corresponds with toxicity remains unclear. Although central nervous system side-effects may correlate with serum level, many adverse effects of clozapine appear to be unrelated, including haematological and cardiac events. There are numerous clinically significant interactions between clozapine and other substances, including prescribed medications, nicotine and caffeine. TDM of clozapine may be of clinical value in certain situations, such as poor clinical response; signs of toxicity; onset of seizures; changes in concurrent medication, caffeine or nicotine; liver disease; and suspected non-compliance. The current literature does not support the routine testing of serum clozapine levels in everyday clinical practice.