A clozapine overdose with markedly elevated serum levels

Predicting clozapine dose required to achieve a therapeutic plasma concentration - A comparison of a population algorithm and three algorithms based on gene variant models

BACKGROUND

Clozapine is the most effective antipsychotic but requires careful titration to therapeutic blood levels. Methods to predict therapeutic doses are based on population data.

AIMS

We aimed to construct a model based on genetic variants which accurately predicted plasma levels for clozapine.

METHOD

We measured clozapine plasma levels in patients on a stable dose of clozapine who were known to be fully compliant. Measured plasma levels were adjusted for sampling time and dose. Hepatic enzyme variants were analysed and models were constructed to predict the required dose. These predictions were compared with a standard population-based algorithm.

RESULTS

We measured plasma clozapine concentrations in 18 adherent patients on stable doses of clozapine and recorded the exact timing of sampling. For the algorithm-predicted dose, the mean difference was -49.9 mg/day ((SD 155.9), r = 0.36) from the actual dose required to give a plasma concentration of 0.35 ng/ml. The gene variant activity score predicted a dose for which the mean difference was -43.5 mg/day ((SD 140.1), r = 0.55). For the gene variant activity score with omeprazole correction predicted dose, the mean difference was -31.0 mg/day ((SD 140.8), r = 0.54), and with the gene variant CYP1A2 inducibility predicted dose the mean difference was 44.9 mg/day ((SD 160.8), r = 0.32).

CONCLUSION

Our gene variant activity score with omeprazole correction gave the best estimate of the clozapine dose required to achieve a minimum therapeutic plasma concentration. The use of this model will allow safer titration of clozapine and may reduce the need for plasma-level monitoring during titration.

Socio-demographic and clinical correlates of lifetime suicide attempts and their impact on quality of life in Chinese schizophrenia patients

This study determines the socio-demographic and clinical correlates of suicide attempts in Chinese schizophrenia outpatients and their impact on patients' quality of life (QOL). Two hundred and fifty-five clinically stable schizophrenia outpatients were randomly selected in Hong Kong (HK) and their counterparts matched according to sex, age, age at onset and length of illness were recruited in Beijing (BJ). All subjects at both sites were interviewed by the same investigator using standardized assessment instruments. Basic socio-demographic and clinical data and history of suicide attempts were collected. The lifetime prevalence of suicide attempts was 26.7% in the whole sample and 20% and 33.6% in the HK and BJ samples, respectively. Patients with a history of suicide attempts were less likely to receive depot antipsychotic (AP) medication, more likely to receive clozapine, benzodiazepines (BZD) and higher doses of APs; were younger at onset, had more hospitalizations; had more severe positive, depressive, anxiety and extrapyramidal (EPS) symptoms; were poorer QOL in the physical, psychological, social and environmental domains; and were more likely to be BJ residents. In multiple logistic regression analysis, early age at onset, poor physical QOL, use of clozapine and BZDs, and study site (HK vs BJ) were significant contributors to lifetime suicide attempts. Significant difference was found between matched samples in HK and BJ with respect to suicide attempts. HK is a cosmopolitan city with a Western social structure and mental health system, whereas in BJ more traditional Chinese cultural values predominate, with a mental health policy radically different from that of HK. These differences suggest that socio-cultural factors play a significant role in determining suicide attempts in schizophrenia.

Hemoperfusion in the treatment of acute clozapine intoxication in China

BACKGROUND AND AIMS

No systematic study has focused on the characteristics and outcome of acute clozapine intoxication, although clozapine is the most widely used antipsychotic agent in China. The study reported herein examined the features of clozapine intoxication and the therapeutic effect of hemoperfusion (HP).

METHODS

In a retrospective chart review, the notes of 47 patients who attempted suicide by ingesting large amounts of clozapine and were treated at the only psychiatric emergency service in Beijing were analyzed. Of the 20 unconscious patients with plasma clozapine concentrations of more than 2000 ng/mL, 14 received a combination of HP and symptomatic treatment, whereas the other 6 and the remaining 27 patients received only symptomatic treatment. Patients' psychiatric conditions and both plasma clozapine and norclozapine concentrations were closely monitored and registered.

RESULTS

One patient died of pulmonary edema and subsequent heart failure, but the rest of the patients recovered without any sequelae. Patients who received HP regained consciousness significantly faster than their counterparts with the same level of clozapine plasma concentration (>2000 ng/mL) who did not receive HP.

CONCLUSIONS

A combination of HP and symptomatic treatment is the best therapeutic option when plasma clozapine concentration is high.

Determination of myocardium to plasma concentration ratios of five antipsychotic drugs: comparison with their ability to induce arrhythmia and sudden death in clinical practice

Reviewing available data shows that most of antipsychotic drugs are associated with arrhythmia and sudden death. Experimental studies have shown a HERG channel blockade, a dose-dependent increase in duration of action potential or of QT interval, with various degrees of indicators of serious arrhythmogenicity. However, it seems difficult to relate these in vitro and in vivo preclinical models to clinical findings, in part, because the relationship between concentrations used and in vivo tissue concentrations during treatment in man is not known. Consequently, we established the myocardium to plasma concentration ratios for a series of antipsychotic drugs by intraperitoneal administration of different level doses to the guinea pig. Then, we compared these values to their ability to induce arrhythmia or torsade de pointes in clinical practice. The myocardium to plasma concentration ratios were 2.2 for clozapine, 2.7 for olanzapine, 3.1 for sertindole, 4.5 for risperidone, and 6.4 for haloperidol. These data suggest that when the ratio is higher than 4, arrhythmia and sudden death may be expected. On the contrary, when the ratio is less than 3, little effect may be predicted. These results underscore the importance of interpreting HERG channel data and electrophysiological data in the context of other pharmacokinetic parameters such as myocardium to plasma distribution.

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.