Clozapine Metabolism in East Asians and Caucasians: A Pilot Exploration of the Prevalence of Poor Metabolizers and a Systematic Review

Semi-physiological Pharmacokinetic Model of Clozapine and Norclozapine in Healthy, Non-smoking Volunteers: The Impact of Race and Genetics

BACKGROUND AND OBJECTIVES: Clozapine is the medication of choice for treatment-resistant schizophrenia. However, it has a complex metabolism and unexplained interindividual variability. The current work aims to develop a pharmacokinetic model of clozapine and norclozapine in non-smokers and assess the impact of demographic and genetic predictors.

METHODS

Healthy volunteers were recruited in a population pharmacokinetic study. Blood samples were collected at 30 min and 1, 2, 3, 5 and 8 h following a single flat dose of clozapine (12.5 mg). The clozapine and norclozapine concentrations were measured via high-performance liquid chromatography-ultraviolet method. A semi-physiological pharmacokinetic model of clozapine and norclozapine was developed using nonlinear mixed-effects modeling. Clinical and genetic predictors were evaluated, including CYP1A2 (rs762551) and ABCB1 (rs2032582), using restriction fragment length polymorphism.

RESULTS

A total of 270 samples were collected from 33 participants. The data were best described using a two-compartment model for clozapine and a two-compartment model for norclozapine with first-order absorption and elimination and pre-systemic metabolism. The estimated (relative standard error) clearance of clozapine and norclozapine were 27 L h-1 (31.5 %) and 19.6 L h-1 (30%), respectively. Clozapine clearance was lower in sub-Saharan Africans (n = 4) and higher in Caucasians (n = 9) than Asians (n = 20). Participants with CYP1A2 (rs762551) (n = 18) and ABCB1 (rs2032582) (n = 12) mutant alleles had lower clozapine clearance in the univariate analysis.

CONCLUSIONS

This is the first study to develop a semi-physiological pharmacokinetic model of clozapine and norclozapine accounting for the pre-systemic metabolism. Asians required lower doses of clozapine as compared with Caucasians, while clozapine pharmacokinetics in sub-Saharan Africans should be further investigated in larger trials.

Clozapine-associated pericarditis and pancreatitis in children and adolescents: A systematic literature review and pharmacovigilance study using the VigiBase database

BACKGROUND

The literature has paid very little attention to pericarditis, pericardial effusion and pancreatitis during clozapine treatment in children and adolescents.

METHODS

Cases of clozapine-associated pericarditis and pancreatitis in children were studied using searches in: 1) PubMed (June 16, 2023), and 2) the World Health Organization's pharmacovigilance database (June 1, 2022), VigiBase. VigiBase uses a logarithmic measure of disproportionality called the information component (IC).

RESULTS

The PubMed search yielded 3 clozapine-associated pericarditis cases, 1 pancreatitis case and 1 with both. VigiBase provided a significant clozapine-associated pericarditis IC = 3.6 with an IC025 = 2.9 (only 3 cases were expected while 22 were observed). VigiBase provided a significant clozapine-associated pancreatitis IC = 2.2 with an IC025 = 1.4 (only 3 cases were expected while 16 were observed). In VigiBase clozapine-associated pericarditis and pericardial effusion in youth looked similar and on a continuum with myocarditis, as myocarditis, pericarditis and pancreatitis appeared to occur mainly during clozapine titration. Combining PubMed and VigiBase we identified: 1) 29 cases of at least possible clozapine-associated pericarditis/pericardial effusion (6 probable and 23 possible) including 7 cases with and 22 without myocarditis, and 2) 17 cases of clozapine-associated pancreatitis (1 definite and 16 possible). Two of the pancreatitis cases occurred during overdoses. No fatal outcomes were found in any clozapine-associated pericarditis and pancreatitis cases.

CONCLUSIONS

Despite the lack of attention in the literature to clozapine-associated pericarditis and pancreatitis, results demonstrate that they can happen in youth, particularly during titration. Pericarditis and pancreatitis appear to be forms of clozapine-associated inflammation during dose titration.

Exploring low clozapine C/D ratios, inverted clozapine-norclozapine ratios and undetectable concentrations as measures of non-adherence in clozapine patients: A literature review and a case series of 17 patients from 3 studies

BACKGROUND

Up to 1/2 of outpatients prescribed clozapine may be partially/fully non-adherent, based on therapeutic drug monitoring (TDM). Three indices for measuring partial/full non-adherence are proposed a: 1) clozapine concentration/dose (C/D) ratio which drops to half or more of what is expected in the patient; 2) clozapine/norclozapine ratio that becomes inverted; and 3) clozapine concentration that becomes non-detectable.

METHODS

These 3 proposed indices are based on a literature review and 17 cases of possible non-adherence from 3 samples: 1) an inpatient study in a Chinese hospital, 2) an inpatient randomized clinical trial in a United States hospital, and 3) and a Uruguayan outpatient study.

RESULTS

The first index of non-adherence is a clozapine C/D ratio which is less than half the ratio corresponding to the patient's specific ancestry group and sex-smoking subgroup. Knowing the minimum therapeutic dose of the patient based on repeated TDM makes it much easier to establish non-adherence. The second index is inverted clozapine/norclozapine ratios in the absence of alternative explanations. The third index is undetectable concentrations. By using half-lives, the chronology of the 3 indices of non-adherence was modeled in two patients: 1) the clozapine C/D ratio dropped to ≥1/2 of what is expected from the patient (around day 2); 2) the clozapine/norclozapine ratio became inverted (around day 3); and 3) the clozapine concentration became undetectable by the laboratory (around days 9-11).

CONCLUSION

Prospective studies should further explore these proposed clozapine indices in average patients, poor metabolizers (3 presented) and ultrarapid metabolizers (2 presented).

Association between initial pattern of clozapine titration, concentration-to-dose ratio, and incidence of fever in patients with schizophrenia spectrum disorders in a Korean tertiary hospital

Safe and effective administration of clozapine requires careful monitoring for inflammatory reactions during the initial titration. The concentration-to-dose (C/D) ratio must be taken into account, which may vary among ethnicities. In this retrospective study, 1408 Korean schizophrenia inpatients were examined for during the first 8 weeks of clozapine titration. The average doses of clozapine administered during weeks 1, 2, 4, and 8 were 77.37, 137.73, 193.20, and 212.83 mg/day, with significantly lower doses for females than males. The average C/D ratio was significantly higher in females (1.75 ± 1.04 and 1.11 ± 0.67 ng/mL per mg/day). Patients with higher C/D ratios were more likely to experience fever and were prescribed lower doses of clozapine starting from week 4. In total, 22.1 % of patients developed a fever at an average of 15.74 days after initiating clozapine. Patients who developed a fever were younger, used more antipsychotics at baseline, had a higher C/D ratio, and had a higher incidence of an elevated C-reactive protein level. A higher C/D ratio, use of a greater number of antipsychotics at baseline, and concomitant olanzapine use were risk factors for the development of inflammatory reactions. The incidence of pneumonia, agranulocytosis, and myocarditis within 8 weeks were 3.7 %, 0.3 %, and 0.1 %. In summary, the target dose of clozapine titration is lower for Korean schizophrenia patients, with a higher C/D ratio and more frequent fever compared to Western patients; however, myocarditis occurs rarely. Our findings may contribute to the titration methods for clozapine for the East Asian population.

Slower clozapine titration than the official Japanese protocol led to fewer inflammatory adverse effects: A retrospective chart review of seven hospitals

BACKGROUND

Higher frequencies of inflammatory adverse effects of clozapine have been reported in Japan. As the international titration protocol for Asians has set slower dose titration than the Japanese package insert, we hypothesized that a dose titration speed slower than the recommendation of the guideline would be associated with fewer inflammatory-related adverse events.

METHODS

The medical records of all 272 patients who were first started on clozapine at seven hospitals between 2009 and 2023 were studied retrospectively. Of those, 241 were included in the analysis. The patients were divided into two groups regarding whether the titration speed was faster or slower than the guideline for Asians. The incidence of inflammatory adverse events with clozapine was compared between the groups.

RESULTS

The frequency of inflammatory adverse events was 34 % (37/110) in the faster titration group and 13 % (17/131) in the slower titration group, and a significant difference was observed by Fisher exact test (odds ratio 3.38; 95 % confidence interval 1.71-6.91; p < 0.001). Serious adverse effects, fever for more than five days, and clozapine discontinuation were significantly more frequent in the faster titration group. Logistic regression analysis indicated significantly more inflammatory adverse events in the faster titration group (adjusted odds ratio 4.01; 95 % confidence interval 2.02-7.87; p < 0.001) considering age, sex, body mass index, concomitant valproic acid, and smoking as confounding factors.

CONCLUSION

Clozapine-induced inflammatory adverse events were less frequent in Japanese individuals when a titration rate was more gradual than the protocol recommended in the Japanese package insert.

The introduction of clozapine at the Nathan Kline Institute in New York and its long-term consequences

Nathan S. Kline was a pioneer in psychopharmacology in the United States (US). In 1952, Kline started a research unit at Rockland State Hospital, New York. Kline brought clozapine from Switzerland since it was not yet available in the US. At Rockland State Hospital, George Simpson had conducted antipsychotic trials and had developed scales to assess movement disorders. In 1974, Simpson published the first US clozapine trial. In 1978, he published on 1) the effect of clozapine on tardive dyskinesia and 2) high plasma clozapine concentrations in two patients with seizures. His experience of clozapine withdrawal symptoms in his first 2 trials led in the future to more articles in this area. In Philadelphia, Simpson designed a double-blind randomized clinical trial (RCT) with 3 doses (100, 300 and 600 mg/day) which was published in 1999. From the 50 patients started on the RCT, 47 provided repeated plasma clozapine concentrations every other week of the RCT. This rich database of plasma clozapine concentrations under controlled conditions has contributed to many of the advances in clozapine pharmacokinetics in the last 5 years including: 1) obesity can be associated with clozapine poor metabolism (PM) status, 2) a clozapine ultrarapid metabolizer (UM) with a minimum therapeutic dose of 1591 mg/day, 3) a case of clozapine intoxication dropped from the RCT due to pneumonia, 4) cases of increased plasma concentrations during clozapine-induced fever, 5) the possibility that African-Americans may need higher clozapine doses than those of European ancestry, and 6) three indices of non-adherence.

A Chinese medicine called Danggui Longhui may be a new clinically relevant clozapine inducer: Two case reports identified by therapeutic drug monitoring

BACKGROUND

Danggui Longhui is a traditional Chinese medicine made from the dried root of Angelica sinensis. It is used in psychiatric patients in China to reduce associated constipation. In a population pharmacokinetic model in olanzapine patients from Beijing Anding Hospital, we demonstrate that dangguilonghui tablets doubled olanzapine clearance, indicating the induction of olanzapine metabolism. Olanzapine metabolism is similar to clozapine metabolism.

METHODS

Two cases of possible clozapine induction using dangguilonghui tablets 4 g/day were identified in Beijing Anding Hospital. Dividing the minimum therapeutic concentration of 350 ng/mL by the concentration-to-dose (C/D) ratio provides the minimum therapeutic dose.

RESULTS

Case 1 was a female smoker on clozapine for 415 days. The mean of 6 clozapine C/D ratios associated with smoking provided a minimum therapeutic dose of 267 mg/day. There were 6 steady-state concentrations on the combination of valproic acid and dangguilonghui tablets, which provided a much higher minimum therapeutic dose of 833 mg/day. Four steady-state clozapine C/D ratios based on smoking and valproate after 4 months of carbamazepine 200 mg/day provided a minimum therapeutic dose of 603 mg/day. Case 2 was a female non-smoker on clozapine for 58 days. She had 3 clozapine C/D ratios on dangguilonghui tablets with a mean of 0.30 ng/mL providing a minimum therapeutic dose of 1167 mg/day.

CONCLUSION

Future clinical studies with repeated measures need to replicate the possibility that dangguilonghui tablets are a moderate-to-strong inducer of clozapine metabolism as suggested by these two limited cases.

A brief history of clozapine in China with a look forward

Clozapine was first manufactured in China in 1976. Clozapine is currently used not only for treatment-refractory schizophrenia (TRS), but also continues to be used in the treatment of patients with non-TRS and other mental disorders; moreover, low-dose clozapine is also used in sedative-hypnotic therapy and in combination with other drugs. There is need for studies in China using various titrations and assessing their risk for myocarditis and aspiration pneumonia. The Chinese clozapine package insert will also greatly benefit from these changes.

Once-daily versus divided dosing regimens of clozapine: A cross-sectional study in Singapore

INTRODUCTION

Clozapine is recognized as the gold standard medication for treatment-resistant schizophrenia. Despite the general recommendation of administering in a divided dosing regimen, clozapine is often prescribed once daily at night in clinical practice. This study aims to compare patient characteristics, psychiatric symptoms, side effects, and plasma concentration of clozapine between once-daily dosing and divided dosing regimens.

METHODS

This cross-sectional study included 159 participants with treatment-resistant schizophrenia or schizoaffective disorder. Participant's demographic information, anthropometric data, and medical history were collected. Their psychiatric symptoms, cognition, functioning, and side effects were evaluated.

RESULTS

Once-daily dosing regimen was associated with younger age and competitive employment. Lower clinical symptom severity, better functioning and cognitive performance were observed in the once-daily dosing group. Lower daily dose of clozapine, trough plasma concentrations of clozapine and norclozapine were also significantly associated with once-daily dosing regimen.

CONCLUSION

The study results support once-daily dosing of clozapine as a viable option to selected patients in clinical practice, as no association of severe symptoms or side effects were associated with once-daily dosing regimen. More studies are needed to examine the relationship between clinical outcomes and clozapine dosing regimen.

Clozapine ultrarapid metabolism during weak induction probably exists but requires careful diagnosis. A literature review, five new cases and a proposed definition

During weak induction (from smoking and/or valproate co-prescription), clozapine ultrarapid metabolizers (UMs) need very high daily doses to reach the minimum therapeutic concentration of 350 ng/ml in plasma; clozapine UMs need clozapine doses higher than: 1) 900 mg/day in patients of European/African ancestry, or 2) 600 mg/day in those of Asian ancestry. Published clozapine UMs include 10 males of European/African ancestry, mainly assessed with single concentrations. Five new clozapine UMs (two of European and three of Asian ancestry) with repeated assessments are described. A US double-blind randomized trial included a 32-year-old male smoking two packages/day with a minimum therapeutic dose of 1,591 mg/day from a single TDM during open treatment of 900 mg/day. In a Turkish inpatient study, a 30-year-old male smoker was a possible clozapine UM needing a minimum therapeutic dose of 1,029 mg/day estimated from two trough steady-state concentrations on 600 mg/day. In a Chinese study, three possible clozapine UMs (all male smokers) were identified. The clozapine minimum therapeutic dose estimated with trough steady-state concentrations >150 ng/ml was: 1) 625 mg/day, based on a mean of 20 concentrations in Case 3; 2) 673 mg/day, based on a mean of 4 concentrations in Case 4; and 3) 648 mg/day, based on a mean of 11 concentrations in Case 5. Based on these limited studies, clozapine UMs during weak induction may account for 1-2% of clozapine-treated patients of European ancestry and <1% of those of Asian ancestry. A clozapine-to-norclozapine ratio <0.5 should not be used to identify clozapine UMs.

Impact of patient-specific factors on clozapine metabolism in individuals with treatment-resistant schizophrenia or schizoaffective disorder

BACKGROUND

There is high inter-individual variability in clozapine metabolism due to genetic and non-genetic differences. Patient-specific factors such as smoking, inflammation indicated by elevated C-reactive protein (CRP), and certain concurrent medications have a significant influence on clozapine metabolism.

AIM

To assess which patient-specific factors best explain variability in clozapine metabolism estimated by clozapine concentration to dose (C/D) ratios.

METHODS

A retrospective cohort analysis using electronic medical data was conducted on 172 inpatients at the BC Psychosis Program. Patients with normal renal and liver function were included if they were on clozapine and had at least one steady-state plasma concentration. The degree of influence of each factor on the variability of clozapine metabolism in the entire cohort and subgroups stratified by fluvoxamine use was evaluated using multiple linear regression analysis of C/D ratios.

RESULTS

Model fit testing showed that the entire cohort model accounts for 52.7% of C/D ratio variability, while the no fluvoxamine and fluvoxamine models accounted for 40.8% and 43.8%. In the entire cohort (n = 172), fluvoxamine use explained the highest variance, and C/D ratios were higher by 30.6% on average. The second strongest predictor was elevated CRP > 10 mg/L, and C/D ratios were higher by 22.9% on average. Subsequently, obesity, nonsmoker status, and female sex explained a significant but modest proportion of variance. Among participants on fluvoxamine (n = 58), only fluvoxamine dose was associated with an increase, and for every 25 mg increase in dose, C/D ratios increased by 5% on average.

CONCLUSION

In a clinical population, this study replicated the relationship between reduced rate of clozapine metabolism and the use of fluvoxamine, elevated CRP, obesity, nonsmoking status, and female sex; and the magnitude of the effects were large enough to be clinically relevant.

Can Slow Personalized Titration Using C-Reactive Protein Monitoring Decrease the High Rates and Mortality of Clozapine-Associated Myocarditis Seen in Some Countries? A Call for Research

PURPOSE/BACKGROUND

The hypothesis that slower personalized titration may prevent clozapine-associated myocarditis and decrease the disproportion incidence of 3% found in Australia was not described in a recent Australian article in this journal.

METHODS

Six countries in addition to Australia have published information suggesting a similar incidence of clozapine-associated myocarditis. On September 19, 2023, PubMed searches were updated for articles from the United States, Korea, Japan, Canada, New Zealand, and Turkey.

FINDINGS/RESULTS

An incidence of 3.5% (4/76) was found in a US hospital, but US experts were the first to propose that clozapine-associated myocarditis may be a hypersensitivity reaction associated with rapid titration and possibly preventable. Koreans and Japanese are of Asian ancestry and need lower minimum therapeutic doses for clozapine than patients of European ancestry. A 0.1% (2/1408) incidence of myocarditis during clozapine titration was found in a Korean hospital, but pneumonia incidence was 3.7% (52/1408). In 7 Japanese hospitals, 34% (37/110) of cases of clozapine-associated inflammation were found during faster titrations (based on the official Japanese titration) versus 13% (17/131) during slower titrations (based on the international titration guideline for average Asian patients). Recent limited studies from Canada, New Zealand, and Turkey suggest that slower personalized titration considering ancestry may help prevent clozapine-associated myocarditis.

IMPLICATIONS/CONCLUSIONS

Other countries have very limited published data on clozapine-associated myocarditis. Based on a recent Australian case series and these non-Australian studies, the author proposes that Australia (and other countries) should use slow personalized titration for clozapine based on ancestry and c-reactive protein monitoring.

A Systematic Review of Clozapine Concentration-Dose Ratio from Therapeutic Drug Monitoring Studies in Children and Adolescents Treated with Clozapine for Mental Disorders

BACKGROUND

Therapeutic drug monitoring of clozapine in children and adolescents has received insufficient attention. Calculation of concentration-to-dose (C/D) ratios from trough steady-state concentrations estimate drug clearance.

METHODS

A systematic electronic literature search was conducted in 3 article databases from inception until January 10, 2023, and articles reporting clozapine concentrations in children and adolescents were retrieved. The pharmacokinetic quality of the studies was assessed, and clozapine C/D ratios were calculated using the sample mean clozapine dose and concentration.

RESULTS

Of the 37 articles of potential interest, only 7 reported clozapine trough and steady-state concentrations. After excluding case reports and a study confounded by fluvoxamine, 4 studies on psychosis from Europe and the United States were included. The clozapine C/D ratios were similar to published adult values and ranged from 0.82 to 1.24 with a weighted mean of 1.08 ng/mL per mg/d. The weighted means were 334 mg/d for the dose and 380 ng/mL for the concentration. The stratified analysis of the weighted mean clozapine C/D ratios from 2 studies showed lower values in 52 male (1.05 ng/mL per mg/d) than in 46 female (1.46 ng/mL per mg/d) children and adolescents, with values similar to those reported for European adult nonsmokers. Two female adolescents had high clozapine C/D ratios (2.54 ng/mL per mg/d), an Asian American patient with borderline obesity and a patient with intellectual disability with low dosage (mean = 102 mg/d) and concentration (mean = 55 ng/mL).

CONCLUSIONS

Reports on clozapine therapeutic drug monitoring in children and adolescents are limited in number and quality. Future studies should focus on basic pharmacokinetic issues, such as stratification by sex, smoking, and relevant comedications with inductive or inhibitory properties.

Comparative Study of the Efficacy and Side Effects of Brand-Name and Generic Clozapine for Long-Term Maintenance Treatment Among Korean Patients With Schizophrenia: A Retrospective Naturalistic Mirror-Image Study

OBJECTIVE

Clozapine is considered the most reliable drug for treatment-resistant schizophrenia. In 2014, a generic formulation of clozapine (Clzapine) was introduced in Korea. This study was performed to provide clinical information regarding the use of clozapine and to compare efficacy and tolerability when converting from the brand-name formulation (Clozaril) to the generic formulation during longterm maintenance treatment among Korean patients with schizophrenia.

METHODS

This mirror-image study retrospectively investigated the electronic medical records of patients who had switched from Clozaril to Clzapine with a ≥1-year duration for each formulation. Clinical data were collected, including information regarding clozapine use, psychiatric hospitalization, co-medications, and blood test findings. Data before and after the switch were compared using paired t-tests.

RESULTS

Among 332 patients, the mean 1-year dosages were 233.32±149.35 mg/day for Clozaril and 217.36±136.66 mg/day for Clzapine. The mean clozapine concentration-to-dose ratios were similar before and after the switch (Clozaril, 1.33±0.68; Clzapine, 1.26±0.80). Switching from Clozaril to Clzapine resulted in no significant differences in the hospitalization rate, hospitalization duration, or laboratory findings (liver function parameters, serum cholesterol level, and serum glucose level). Equivalent doses of co-prescribed antidepressants were decreased, but concomitant medications otherwise showed no significant differences.

CONCLUSION

Clinical efficacy and tolerability appear comparable when switching to Clzapine during clozapine maintenance treatment. This study offers descriptive real-world clinical insights into clozapine maintenance treatment in Korea, thereby providing patients with more treatment options and contributing to the development of maintenance guidelines tailored to the Korean population.

Abnormal blood concentration changes in a 71-year-old female who survived a 10,000mg overdose of clozapine: a case report

BACKGROUND

Clozapine is a highly effective second-generation antipsychotic with few extrapyramidal reactions, making it a preferred choice among clinicians. However, instances of acute clozapine poisoning resulting from suicide attempts and misuse have been reported. Through our review of existing literature, we identified that we believe to be the highest recorded overdose of clozapine in elderly patients, resulting in a nonfatal outcome.

CASE PRESENTATION

The case report involves a 71-year-old female with a history of depression who ingested a dose of 10,000 mg of clozapine. Approximately 6 h after the overdose, the clozapine level was 5,200 μg/L, significantly surpassing the recommended therapeutic concentration range of 350-600 μg/L. After gastric lavage and hemoperfusion, the blood level dropped to 1847.11 μg/L. Notably, during therapeutic drugs monitoring (TDM), we found a perplexing spike in the patient's blood level to 5554.15 μg/L after the second hemoperfusion.

CONCLUSION

In this case we mainly focused on the abnormal fluctuations in the concentration of clozapine. We conducted a comprehensive analysis of potential factors contributing to this abnormal phenomenon in terms of the patient's age, clinical symptoms, various laboratory test indexes, and the pharmacokinetics of clozapine. Our findings underscore the importance of timely TDM and the precision of results in managing elderly patients experiencing high-dose clozapine poisoning.

Will ChatGPT3 Substitute for us as Clozapine Experts?

BACKGROUND

ChatGPT3 is a new artificial intelligence program released on February 13, 2023.

METHOD

The authors tested ChatGPT3 on February 18, 2023, and repeated the test a week later. They used their expertise on the effects of ethnic ancestry in the stratification of clozapine dosing and the new idea that they published in March 2022 that African-Americans need higher clozapine doses because they have higher clozapine clearance.

RESULTS

In the first interaction on February 18, ChatGPT3 provided reasonable and very up-to-date information, which included a comment that patients of African ancestry have higher clozapine metabolism. The other 4 interactions became progressively more concerning as we asked ChatGPT3 to provide references to justify the latter statement. ChatGPT3 provided non-existent "references" using articles from real journals, with real authors, false PubMed identifiers, and false titles. Moreover, ChatGPT3 said that the first author wrote in 2003 that African-Americans had higher CYP1A2 activity when that did not happen until 2022. One week later, the second author repeated the same set of questions. This time ChatGPT3 described the opposite, that African-Americans have "lower" CYP1A2 activity and "slower" metabolism. ChatGPT3 provided another set of articles to justify the information; some were real but did not comment on clozapine metabolism in African-Americans while others did not exist.

CONCLUSIONS

ChatGPT3 provided a mixture of truth, twisted reality, and non-existent "facts." Within one week it defended opposite positions regarding a clinically relevant issue such as using higher or lower clozapine doses in African-Americans.

Valproate-related neutropenia and lithium-related leukocytosis in patients treated with clozapine: a retrospective cohort study

BACKGROUND

Neutropenia is a noteworthy side effect of clozapine, which might warrant this drugs' discontinuance for safety. Studies have revealed that the risk of neutropenia increases with concurrent administration of valproate, but the evidence was limited. Conversely, lithium may have an ameliorating effect on clozapine-induced neutropenia. This study explored the effects of valproate and lithium on white blood cell counts in patients treated with clozapine.

METHODS

We retrospectively investigated the electronic medical records from one tertiary psychiatric hospital in Taiwan and enrolled patients discharged between January 1, 2006, and December 31, 2017, with clozapine prescriptions. We scrutinized their demographic data, medications, and hematological results at discharge and during follow-up outpatient clinic visits over the subsequent 3 years. Patients were classified into four groups: clozapine only (CLO), clozapine and valproate (CLO + VAL), clozapine and lithium (CLO + Li), and clozapine, valproate, and lithium (CLO + VAL + Li). We also identified hematological events (neutropenia or leukocytosis) of these patients during outpatient follow-ups.

RESULTS

Of the included 1084 patients, 55(5.1%) developed neutropenia. Concurrent valproate use (odds ratio [OR] = 3.49) and older age (p = .007) were identified as risk factors. Moreover, 453 (41.79%) patients developed leukocytosis. Younger age; male sex; and concurrent use of lithium (OR = 3.39, p < .001), clozapine daily dosage, and benzodiazepines were the risk factors for leukocytosis.

CONCLUSION

Concurrent valproate use and older age are associated with the development of neutropenia in patients treated with clozapine. Concurrent lithium usage, younger age, male sex, and concurrent benzodiazepine use might be related to leukocytosis.

Clozapine: Dose, Sex, Ethnicity, Smoking Habit, Age, Body Weight, and Plasma Clozapine and N -Desmethylclozapine (Norclozapine) Concentrations in Clinical Practice

BACKGROUND

Guidance on clozapine dosing in treatment refractory schizophrenia is based largely on data from young adult male White patients.

AIM

This study aimed to audit the plasma clozapine and N -desmethylclozapine (norclozapine) concentrations attained in male and female patients of different ethnicity and smoking habit.

METHOD

The effect of dose, sex, ethnicity, age, body weight, and smoking habit on plasma clozapine and norclozapine concentrations were studied using data from a therapeutic drug monitoring service, 1993 to 2017.

RESULTS

There were 371,610 samples (48,098 patients, 32,855 male). Ethnicity was recorded for 763 Afro-Caribbean, 536 Asian, and 7940 White patients. Males were prescribed significantly higher median doses than females but attained significantly lower median plasma clozapine and norclozapine concentrations. Asian and Afro-Caribbean males were prescribed significantly lower and higher median doses, respectively, than White males but attained significantly higher and lower median plasma clozapine and norclozapine concentrations, respectively. Data from 78,431 samples (23,516 patients) were analyzed using a linear mixed model. The predicted dose to attain a predose plasma clozapine concentration of 0.35 mg/L in a nonsmoking White male aged 40 years, with weight of 70 kg, and plasma clozapine-norclozapine ratio of 1.32 was 344 mg/d (95% confidence interval, 227-526 mg/d). The predicted dose was 33% higher and 20% lower in otherwise analogous Afro-Caribbean and Asian patients, respectively. In all cases, the predicted dose was increased by 36% in smokers and decreased by 22% in females.

CONCLUSIONS

Research is needed to further investigate the complex relationships between dose, sex, ethnicity, plasma clozapine and norclozapine concentrations, and clinical outcome such as weight gain.

A comparison of clinical characteristics of psychiatric inpatients in three hospitals from Western China and America

BACKGROUND

Different countries have differences in social and cultural context and health system, which may affect the clinical characteristics of psychiatric inpatients. This study was the first to compare cross-cultural differences in the clinical characteristics of psychiatric inpatients in three hospitals from Western China and America.

METHODS

Overall, 905 and 1318 patients from three hospitals, one in America and two in Western China, respectively, were included. We used a standardised protocol and data collection procedure to record inpatients' sociodemographic and clinical characteristics.

RESULTS

Significant differences were found between hospitals from the two countries. Positive symptoms were the main reason for admission in the Chinese hospitals, while reported suicide and self-injury symptoms more frequently led to hospital admission in America. Moreover, there were more inpatients with combined substance abuse in the American hospital (97.6% vs. 1.9%, P < 0.001). The length of stay (LOS) in America was generally shorter than in China (10.5 ± 11.9 vs. 20.7 ± 13.4, P < 0.001). The dosage of antipsychotic drugs used in the American hospital was higher than in China (275.1 ± 306.9 mg vs. 238.3 ± 212.5 mg, P = 0.002). Regression analysis showed that male sex, older age, retirees, being admitted because of physical symptoms, and using higher doses of antipsychotic drugs were significantly associated with longer hospitalisation in the American hospital (P < 0.05). Comparatively, patients who were divorced, experiencing suicidal ideation, admitted involuntarily, admitted because of physical, depression, or anxiety symptoms, and using higher doses of antipsychotic drugs had longer hospitalisation in Chinese hospitals (P < 0.05).

CONCLUSION

Significant variations in clinical characteristics of inpatients were found between hospitals from Western China and America. The LOS in Chinese hospitals was significantly longer, but patients used higher doses of antipsychotic drugs in the American hospital. Admission due to physical symptoms and the use of higher dosage drugs were related to longer LOS in both countries.

Clozapine prescription rates in Southeast Europe: A cross-sectional study

Introduction

International reports indicate that clozapine is under prescribed. Yet, this has not been explored in Southeast European (SEE) countries. This cross-sectional study investigates clozapine prescription rates in a sample of 401 outpatients with psychosis from Bosnia and Herzegovina, Kosovo by United Nations resolution, North Macedonia, Montenegro and Serbia.

Methods

Descriptive analysis was used to explore clozapine prescription rates; daily antipsychotic dosage was calculated and converted into olanzapine equivalents. Patients receiving clozapine were compared to those not receiving clozapine; next those that were on clozapine monotherapy were compared to those who were on clozapine polytherapy regime.

Results

It was showed that clozapine was prescribed to 37.7% of patients (with cross-country variation: from 25% in North Macedonia to 43.8% in Montenegro), with average dose of 130.7 mg/daily. The majority of patients on clozapine (70.5%) were prescribed at least one more antipsychotic (the most frequent combination was with haloperidol).

Discussion

Our findings suggested that clozapine prescription rate in SEE outpatients is higher than in Western Europe. The average dose is significantly below the optimal therapeutic dosage recommended by clinical guidelines, and clozapine polytherapy is common. This might indicate that clozapine is prescribed mainly for its sedative effect rather than antipsychotic. We hope that this finding will be taken up by relevant stakeholders to address this non-evidence-based practice.

Clozapine-induced myocarditis in children and adolescents: a pharmacovigilance study using VigiBase and a systematic literature review

INTRODUCTION

Clozapine-induced myocarditis in children (age ≤18 yo) was studied from a PubMed search (18 July 2022) (9 cases) and from the World Health Organization's pharmacovigilance database, called Vigibase, of adverse drug reaction (ADR) reports (72 non-duplicated cases). VigiBase uses a logarithmic measure of disproportionality called the information component (IC). A logistic regression model of presence/absence (40/32) of seriousness in VigiBase was developed.

AREAS COVERED

VigiBase provided a significant myocarditis IC = 4.2 with an IC₀₂₅ = 3.8; only 4 clozapine-induced myocarditis cases were expected, while 72 were observed. The PubMed search identified 9 cases, while VigiBase identified 72 cases (of which 67 did not overlap with published cases). These 76 combined cases included 35 doubtful (most with missing information on the day of diagnosis), 19 possible and 22 probable, according to the ADR scale. After adjusting for confounders, quetiapine increased the risk of seriousness with an odds ratio (OR) of 17.6 (95% confidence interval CI, 1.56 to 198.6), while Australian origin decreased it with an OR = 0.13 (CI, 0.04 to 0.47).

EXPERT OPINION

These 41 cases of at least possible clozapine-induced myocarditis indicated that this ADR can definitively occur in children, particularly in the first 30 days of up-titration. Children's and adult cases appeared similar.

The Modernization of Clozapine: A Recapitulation of the Past in the United States and the View Forward

PURPOSE

Although clozapine was Food and Drug Administration (FDA) approved more than 3 decades ago, major barriers and gaps in knowledge continue to prevent its effective and safe use. We review modern-day problems encountered with clozapine in the United States (US).

METHODS

Information surrounding current administrative, clinical, research, and technological gaps or barriers related to clozapine use in the US was reviewed.

FINDINGS

The history of how clozapine became FDA approved likely contributes to gaps in knowledge. The frequency of safety warnings added to the FDA prescribing information may add to fears about clozapine, as evidence by numerous published survey studies. The clozapine Risk Evaluation and Mitigation Strategy (REMS) program has been modified several times in the last decade, causing access and safety issues for patients, which are discussed. Evidence may suggest that the FDA REMS requirements for hematologic monitoring are too cumbersome, and there may be ability to safely loosen requirements. The COVID-19 pandemic brought forth the ability for extended interval monitoring but also greater awareness of the clozapine-inflammation interaction. Newer guidelines published describe considerations in personalizing clozapine titration based on principles of ethnopsychopharmacology. Emerging technologies to support the use of clozapine are not widely available.

IMPLICATIONS

Clozapine is a unique life-saving drug but it is underused in the US, despite its established efficacy. The 2021 REMS changes led to significant difficulties for providers and patients. We highlight the importance of the clozapine-inflammation interaction, therapeutic drug monitoring, and the ability for individual care based on patient-specific factors. There is an urgent need for advancing technology used for clozapine monitoring, evaluating barriers created by REMS, and establishing consistent practices throughout the US.

Clozapine-associated myocarditis in the World Health Organization's pharmacovigilance database: Focus on reports from various countries

INTRODUCTION

The incidence of clozapine-associated myocarditis varies by country. These variations were explored in VigiBase, the World Health Organization's global database which has >25 million spontaneously reported adverse drug reaction (ADR) reports from 145 national drug agencies.

METHODS

On January 15, 2021, a search of VigiBase since inception focused on myocarditis in clozapine patients. The 3572 individual reports were studied using the standard VigiBase logarithmic measure of disproportionality called information component (IC). The IC measures the disproportionality between the expected and the reported rates. After duplicates were eliminated there were 3274 different patients with myocarditis studied in logistic regression models.

RESULTS

The first case was published in 1980 but since 1993 the VigiBase clozapine-myocarditis IC has been significant; moreover, currently it is very strong (IC=6.0, IC₀₀₅-IC₉₉₅=5.9-6.1) and statistically significantly different from other antipsychotics. Of the 3274 different patients with myocarditis, 43.4% were non-serious cases, 51.8% were serious but non-fatal, and 4.8% were fatal. More than half (1621/3274) of the reports came from Australia, of which 69.2% were non-serious, 27.7% serious but non-fatal, and 3.1% fatal. Asian countries contributed only 41 cases.

CONCLUSIONS

In pharmacovigilance studies, confounding factors may explain statistical associations, but the strength and robustness of these results are compatible with the hypothesis that myocarditis is definitively associated with early clozapine treatment (84% [1309/1560] and 5% [82/1560] in the first and second months). Myocarditis reports from Australia are over-represented to a major degree. Asian countries may be underreporting myocarditis to their drug agencies.

A Guideline and Checklist for Initiating and Managing Clozapine Treatment in Patients with Treatment-Resistant Schizophrenia

Treatment-resistant schizophrenia (TRS) will affect about one in three patients with schizophrenia. Clozapine is the only treatment approved for TRS, and patients should be treated as soon as possible to improve their chances of achieving remission. Despite its effectiveness, concern over side effects, monitoring requirements, and inexperience with prescribing often result in long delays that can expose patients to unnecessary risks and compromise their chances of achieving favorable long-term outcomes. We critically reviewed the literature on clozapine use in TRS, focusing on guidelines, systematic reviews, and algorithms to identify strategies for improving clozapine safety and tolerability. Based on this, we have provided an overview of strategies to support early initiation of clozapine in patients with TRS based on the latest evidence and our clinical experience, and have summarized the key elements in a practical, evidence-based checklist for identifying and managing patients with TRS, with the aim of increasing confidence in prescribing and monitoring clozapine therapy.

An International Adult Guideline for Making Clozapine Titration Safer by Using Six Ancestry-Based Personalized Dosing Titrations, CRP, and Clozapine Levels

This international guideline proposes improving clozapine package inserts worldwide by using ancestry-based dosing and titration. Adverse drug reaction (ADR) databases suggest that clozapine is the third most toxic drug in the United States (US), and it produces four times higher worldwide pneumonia mortality than that by agranulocytosis or myocarditis. For trough steady-state clozapine serum concentrations, the therapeutic reference range is narrow, from 350 to 600 ng/mL with the potential for toxicity and ADRs as concentrations increase. Clozapine is mainly metabolized by CYP1A2 (female non-smokers, the lowest dose; male smokers, the highest dose). Poor metabolizer status through phenotypic conversion is associated with co-prescription of inhibitors (including oral contraceptives and valproate), obesity, or inflammation with C-reactive protein (CRP) elevations. The Asian population (Pakistan to Japan) or the Americas' original inhabitants have lower CYP1A2 activity and require lower clozapine doses to reach concentrations of 350 ng/mL. In the US, daily doses of 300-600 mg/day are recommended. Slow personalized titration may prevent early ADRs (including syncope, myocarditis, and pneumonia). This guideline defines six personalized titration schedules for inpatients: 1) ancestry from Asia or the original people from the Americas with lower metabolism (obesity or valproate) needing minimum therapeutic dosages of 75-150 mg/day, 2) ancestry from Asia or the original people from the Americas with average metabolism needing 175-300 mg/day, 3) European/Western Asian ancestry with lower metabolism (obesity or valproate) needing 100-200 mg/day, 4) European/Western Asian ancestry with average metabolism needing 250-400 mg/day, 5) in the US with ancestries other than from Asia or the original people from the Americas with lower clozapine metabolism (obesity or valproate) needing 150-300 mg/day, and 6) in the US with ancestries other than from Asia or the original people from the Americas with average clozapine metabolism needing 300-600 mg/day. Baseline and weekly CRP monitoring for at least four weeks is required to identify any inflammation, including inflammation secondary to clozapine rapid titration.

Clozapine resistant schizophrenia: Newer avenues of management

About 40%-70% of the patients with treatment-resistant schizophrenia have a poor response to adequate treatment with clozapine. The impact of clozapine-resistant schizophrenia (CRS) is even greater than that of treatment resistance in terms of severe and persistent symptoms, relapses and hospitalizations, poorer quality of life, and healthcare costs. Such serious consequences often compel clinicians to try different augmentation strategies to enhance the inadequate clozapine response in CRS. Unfortunately, a large body of evidence has shown that antipsychotics, antidepressants, mood stabilizers, electroconvulsive therapy, and cognitive-behavioural therapy are mostly ineffective in augmenting clozapine response. When beneficial effects of augmentation have been found, they are usually small and of doubtful clinical significance or based on low-quality evidence. Therefore, newer treatment approaches that go beyond the evidence are needed. The options proposed include developing a clinical consensus about the augmentation strategies that are most likely to be effective and using them sequentially in patients with CRS. Secondly, newer approaches such as augmentation with long-acting antipsychotic injections or multi-component psychosocial interventions could be considered. Lastly, perhaps the most effective way to deal with CRS would be to optimize clozapine treatment, which might prevent clozapine resistance from developing. Personalized dosing, adequate treatment durations, management of side effects and non-adherence, collaboration with patients and caregivers, and addressing clinician barriers to clozapine use are the principal ways of ensuring optimal clozapine treatment. At present, these three options could the best way to manage CRS until research provides more firm directions about the effective options for augmenting clozapine response.

Clozapine-associated myocarditis in the World Health Organization's pharmacovigilance database: Focus on reports from various countries

INTRODUCTION

The incidence of clozapine-associated myocarditis varies by country. These variations were explored in VigiBase, the World Health Organization's global database which has >25 million spontaneously reported adverse drug reaction (ADR) reports from 145 national drug agencies.

METHODS

On January 15, 2021, a search of VigiBase since inception focused on myocarditis in clozapine patients. The 3572 individual reports were studied using the standard VigiBase logarithmic measure of disproportionality called information component (IC). The IC measures the disproportionality between the expected and the reported rates. After duplicates were eliminated there were 3274 different patients with myocarditis studied in logistic regression models.

RESULTS

The first case was published in 1980 but since 1993 the VigiBase clozapine-myocarditis IC has been significant; moreover, currently it is very strong (IC=6.0, IC005-IC995=5.9-6.1) and statistically significantly different from other antipsychotics. Of the 3274 different patients with myocarditis, 43.4% were non-serious cases, 51.8% were serious but non-fatal, and 4.8% were fatal. More than half (1621/3274) of the reports came from Australia, of which 69.2% were non-serious, 27.7% serious but non-fatal, and 3.1% fatal. Asian countries contributed only 41 cases.

CONCLUSIONS

In pharmacovigilance studies, confounding factors may explain statistical associations, but the strength and robustness of these results are compatible with the hypothesis that myocarditis is definitively associated with early clozapine treatment (84% [1309/1560] and 5% [82/1560] in the first and second months). Myocarditis reports from Australia are over-represented to a major degree. Asian countries may be underreporting myocarditis to their drug agencies.

The Impact of Smoking, Sex, Infection, and Comedication Administration on Oral Olanzapine: A Population Pharmacokinetic Model in Chinese Psychiatric Patients

BACKGROUND AND OBJECTIVE: Prior olanzapine population pharmacokinetic (PPK) models have focused on the effects of sex and smoking on olanzapine clearance. This PPK model in Chinese adult psychiatric patients also investigated the influence of comedications and co-occurrence of infections on olanzapine clearance, and explored how to personalize oral olanzapine dosage in the clinical setting.

METHODS

A total of 1546 serum concentrations from 354 patients were collected in this study. A one-compartment model with first-order absorption was employed to develop the PPK model using a nonlinear mixed-effects modeling approach. Covariates included demographic parameters, co-occurrence of infection and concomitant medications (including dangguilonghui tablets, a Chinese herbal medicine for constipation). Bootstrap validation (1000 runs) and external validation of 50 patients were employed to evaluate the final model. Simulations were performed to explore the personalization of olanzapine dosing after stratification by sex, smoking, and comedication with valproate.

RESULTS

Typical estimates for the absorption rate constant (K_a), apparent clearance (CL/F), and apparent distribution volume (V/F) were 0.30 h^-1, 12.88 L/h, and 754.41 L, respectively. Olanzapine clearance was increased by the following variables: 1.23-fold by male sex, 1.23-fold by smoking, 1.23-fold by comedication with valproate, 1.16-fold by sertraline, and 2.01-fold by dangguilonghui tablets. Olanzapine clearance was decreased by the following variables: 0.75-fold by co-occurrence of infection, 0.70-fold by fluvoxamine, and 0.78-fold by perphenazine. The model evaluation indicated that the final model's performance was good, stable, and precise.

CONCLUSION

This study contributes to the personalization of oral olanzapine dosing, but further studies should be performed to verify the effects of infection and comedications, including valproate and dangguilonghui.

European Whites May Need Lower Minimum Therapeutic Clozapine Doses Than Those Customarily Proposed

PURPOSE/BACKGROUND

A nomogram from a British naturalistic study proposed that the clozapine dosing needed to reach a serum concentration of 350 ng/mL ranged from 265 mg/d (female nonsmokers) to 525 mg/d (male smokers). Some European reviews have used these dosing recommendations, which seem greater than what we found in an Italian White sample ranging from 245 mg/d (female nonsmokers) to 299 mg/d (male smokers). Five other published samples of European Whites were added to the Italian sample to estimate clozapine doses recommended for reaching 350 ng/mL.

METHODS/PROCEDURES

Average clozapine metabolizers were obtained by eliminating outliers with confounding variables: (1) psychiatric inducers and inhibitors; (2) doses less than 100 mg/d; and (3) when possible, patients with inflammation, obesity, or using oral contraceptives. The study included 1363 average metabolizer European Whites: the Italian sample and 5 new samples. Mean averages that reached serum concentration levels of 350 ng/mL were calculated after stratification by sex and smoking status in each sample. Then, weighted mean averages were obtained by combining the 6 samples.

FINDINGS/RESULTS

The estimated weighted mean clozapine dosages ranged from 236 to 368 mg/d (236 mg/d in 218 female nonsmokers, 256 mg/d in 340 male nonsmokers, 357 mg/d in 269 female smokers, and 368 mg/d in 546 male smokers).

IMPLICATIONS/CONCLUSIONS

Our recommended dosages are less than those recommended in Europe. Future studies in European Whites need to replicate these recommended doses for average metabolizer patients after sex and smoking stratification and further explore clozapine dosing for those with relevant clinical confounders.

The relationship between plasma clozapine concentration and clinical outcome: a cross-sectional study

OBJECTIVE

There is no report that statistically evaluates the therapeutic reference (350-600 ng/ml) and adverse drug reaction (ADR) range (>1000 ng/ml) of clozapine (CLZ) recommended by the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) consensus guidelines in an isolated and large sampling study.

METHODS

We administered CLZ to 131 Japanese patients with treatment-resistant schizophrenia in a multicenter cross-sectional study. Plasma CLZ concentrations were assayed by high-performance liquid chromatography using trough sampling. The Brief Psychiatric Rating Scale (BPRS) and severe dose-dependent ADR (sedation, myoclonus, and seizures) were analyzed statistically after adjusting for possible confounders.

RESULTS

The daily CLZ dosage showed a moderately positive relationship with the plasma concentration (r = 0.49, p < 0.001). Every 100 ng/ml increase in plasma CLZ concentration improved the total BPRS score 1.95% (95% CI: 0.89-3.01, p < 0.001) and the odds ratio (OR) 1.38 (95% CI: 1.14-1.66, p = 0.001) for BPRS response. Compared with concentrations below 350 ng/ml CLZ, 350-600 ng/ml (11.12%; 95% CI: 2.52-19.72, p = 0.012) and 600-1000 ng/ml (11.05%; 95% CI: 2.40-19.71, p = 0.013) showed significant improvement in the total BPRS score. Dosages above 1000 ng/ml showed greater improvement (25.36%; 95% CI: 13.08-37.64, p < 0.001) of the total BPRS score but more severe ADRs than dosages below 1000 ng/ml (OR: 31.72; 95% CI: 1.04-968.81, p = 0.048).

CONCLUSION

The AGNP therapeutic reference range (350-600 ng/ml) is useful, and a dose above 1000 ng/ml is potentially more effective but carries the risk of severe ADRs in the central nervous system.

Clozapine prescribing: comparison of clozapine dosage and plasma levels between White British and Bangladeshi patients

AIMS AND METHOD

To compare differences in clozapine doses and plasma levels between Bangladeshi and White British patients. Following ethical approval we identified all current Bangladeshi and White British patients on clozapine maintenance in an east London clinic. We carried out univariate and multivariate regression analyses to examine associations between clozapine doses and ethnicity, age, gender, smoking status and weight. We also compared plasma clozapine levels of the two groups.

RESULTS

On univariate analysis White British patients had on average 85 mg higher doses than Bangladeshi patients (P = 0.004). Older age, male gender and smoking were also associated with higher dose. On multivariate analysis only age and smoking status remained significant. A greater proportion of Bangladeshi patients had high plasma clozapine levels compared with White British (30.76% v. 20.75%), although the difference was not statistically significant.

CLINICAL IMPLICATIONS

Our findings point to the need for the broadening of data collection on ethnic differences in clozapine prescribing within big data-sets such as Prescribing Observatory for Mental Health (POM-UK). Ethnopharmacological variations can inform more person-centred guidance on prescribing.

Elevated Clozapine Concentrations in Clozapine-Treated Patients with Hypersalivation

BACKGROUND AND OBJECTIVE

Hypersalivation is a common, clozapine-related adverse drug reaction with a serious impact on quality of life. Pharmacokinetic correlates of clozapine-related hypersalivation have evaded attention. The purpose of this study was to compare pharmacokinetic parameters between clozapine-treated patients with vs. without hypersalivation from a large therapeutic drug monitoring database.

METHODS

Out of a large therapeutic drug monitoring dataset of clozapine-treated patients, we compared a group of patients with hypersalivation (n = 72) and a control group of patients without any adverse reactions in this regard (n = 323). Comparisons included plasma concentrations and concentrations-by-dose as well as demographic characteristics between groups. Post-hoc analyses were performed separately in smokers and non-smokers. We used the non-parametric Mann-Whitney U test and the chi-square test, while effects of confounders were assessed using a bootstrapping analysis of covariance.

RESULTS

Patients with hypersalivation had higher clozapine plasma concentrations and concentrations-by-dose (p < 0.001 for the Mann-Whitney U test in both cases). Groups did not differ regarding demographic characteristics except for clozapine daily dose and percentage of smokers (p = 0.005 for the Mann-Whitney U test and p = 0.028 for the chi-square test, respectively). There were fewer smokers across patients with hypersalivation compared with patients without and daily doses were higher in patients with hypersalivation. After analysis of covariance, differences remained for both plasma concentrations and concentrations-by-dose (p < 0.001 for both). Post hoc analyses in smokers and non-smokers separately reported similar findings.

CONCLUSIONS

Elevated clozapine plasma concentrations and higher concentrations-by-dose were observed in patients with hypersalivation. A potential role for therapeutic drug monitoring in the prevention or management of clozapine-related hypersalivation is suggested.

Do Indian patients with schizophrenia need half the recommended clozapine dose to achieve therapeutic serum level? An exploratory study

Inter-racial differences in serum clozapine have received less scientific importance, as there are fewer studies on therapeutic drug monitoring (TDM) from Asia. We measured the serum clozapine levels in 142 patients with schizophrenia and related disorders at a tertiary care psychiatric institute in India. The clozapine concentration per milligram (mg) of oral clozapine dose (C/D ratio) was calculated, and the C/D ratio was used to estimate oral clozapine dose needed to achieve therapeutic serum clozapine level (350 ng/ml). This study examined Indian patients only and compared the results with weighted mean serum clozapine and its correlates in Caucasian population, based on published scientific literature. The median C/D ratio in our sample was 2.5 (n = 142), and the clozapine dose needed to achieve therapeutic serum clozapine level was 140 mg/d. The median C/D ratio of our subjects was nearly two and a half times higher than the weighted mean C/D ratio of Caucasians (2.5 v/s 1.07) reported elsewhere. After excluding the significant pharmacokinetic interactions and stratifying according to gender and smoking status, the estimated clozapine dose to achieve therapeutic serum level in male smokers (n = 9) and female non-smokers (n = 38) were 238 mg/d (C/D ratio; 1.47) and 120 mg/d (C/D ratio:2.93) respectively. On comparing, male smokers (600 mg/d versus 238 mg/d) and female non-smokers (300 mg/d versus 120 mg/d) in our study needed about 40% of the recommended clozapine dose for Caucasians to achieve therapeutic serum clozapine level. The pharmacogenetic correlates of lesser clozapine dose requirement in the Indian population require further research.

Using therapeutic drug monitoring to personalize clozapine dosing in Asians

This narrative review on clozapine blood levels or therapeutic drug monitoring (TDM) includes sections focused on drug clearance and TDM, personalized dosing with TDM, clinical applications of TDM in Asians, and areas needing further study. Asian patients need half the clozapine dose (D) used in the United States to get the same blood concentrations (C). The concentration-to-dose (C/D) ratio measures drug clearance. In the United States, the average clozapine patient usually needs from 300 to 600 mg/day to reach 350 ng/mL. US male smokers reach this therapeutic C with a D of 600 mg/day (C/D ratio of 0.60 = 600/350), whereas US female nonsmokers usually need a D of 300 mg/day (C/D ratio of 1.17 = 300/350). While in the United States, average CLO C/D ratios typically are 0.6-1.2 ng/mL per mg/day, in Asian populations they range from 1.20 in male smokers to 2.40 in female smokers, requiring Ds of 300 to 150 mg/day to obtain 350 ng/mL. Asian patients can become clozapine poor metabolizers (PMs), needing very low Ds (50-150 mg/day) to get therapeutic Cs, by taking inhibitors (fluvoxamine, oral contraceptives and valproic acid), due to obesity, or during inflammations with systemic effects. In 573 Asian patients from five samples, around 1% were PMs due to taking inhibitors, 1% due to inflammation, 1% due to obesity, and 7% were potential genetic PMs. The potential genetic PMs ranged between 3% and 13%, but this prevalence will have to be better established in future studies including genetic testing for possible CYP1A2 mutations, which may explain PM status.

Exploring the Prevalence of Clozapine Phenotypic Poor Metabolizers in 4 Asian Samples: They Ranged Between 2% and 13

PURPOSE/BACKGROUND

Clozapine clearance is influenced by sex, smoking status, ethnicity, coprescription of inducers or inhibitors, obesity, and inflammation. In 126 Beijing inpatients, we measured repeated trough steady-state serum concentrations and identified 4% (5/126) who were phenotypical poor metabolizers (PMs); none were ultrarapid metabolizers (UMs). They were defined as being 2 SDs beyond the means of total clozapine concentration/dose ratios stratified by sex and smoking. Using this definition, this study explores the prevalence of PMs and UMs using data from 4 already published Asian samples. Three samples were East Asian (Beijing 2, Taipei, and Seoul); one was from South India (Vellore).

FINDINGS/RESULTS

The prevalence of phenotypical PMs ranged from 2% to 13%, but inflammation was not excluded. The prevalence was 7% (14/191) for Beijing 2, 11% (8/70) for Taipei, 13% (9/67) for Seoul, and 2% (2/101) for the Vellore sample. Five phenotypic PMs appeared to be associated with extreme obesity. Phenotypic UM prevalence ranged from 0% to 1.6% but may be partly explained by lack of adherence. A Vellore phenotypic UM appeared to be associated with induction through high coffee intake.

IMPLICATIONS/CONCLUSIONS

Approximately 10% of Asians may be clozapine PMs and may need only 50 to 150 mg/d to get therapeutic concentrations. Future studies combining gene sequencing for new alleles with repeated concentrations and careful control of confounders including inhibitors, inflammation, and obesity should provide better estimations of the prevalence of phenotypic clozapine PMs across races. Clozapine UM studies require excluding potent inducers, careful supervision of compliance in inpatient settings, and multiple serum concentrations.

Clozapine is strongly associated with the risk of pneumonia and inflammation

Clinicians need to remember that (1) systemic inflammations can increase clozapine level; (2) clozapine, by itself, can cause inflammation, particularly during titration that is too rapid for that patient; (3) clozapine may increase the risk of infection; and (4) more specifically, clozapine may be particularly strongly associated with the risk of pneumonia. Pneumonia appears to be associated with high mortality in clozapine patients around the world. Clinicians who are alert to the risk of pneumonia in clozapine patients may significantly decrease mortality in clozapine patients. There is no data on COVID-19 infections in clozapine patients, but based on what we know about clozapine pharmacology, we can hypothesise that clozapine, possibly by impairing immunological mechanisms, may increase the risk of pneumonia in infected patients. More importantly, once fever and/or pneumonia develops, the clozapine dose should be cut in half to decrease the risk of clozapine intoxication. If there is any doubt that in spite of halving the dose there are still signs of clozapine intoxication, completely stopping clozapine may be indicated. Once the signs of inflammation and fever have disappeared, the clozapine dose can be increased to the prior dosage level.

A Rational Use of Clozapine Based on Adverse Drug Reactions, Pharmacokinetics, and Clinical Pharmacopsychology

Using Richardson and Davidson's model and the sciences of pharmacokinetics and clinical pharmacopsychology, this article reviewed the: (1) poor life expectancy associated with treatment-resistant schizophrenia (TRS), which may be improved in patients who adhere to clozapine; (2) findings that clozapine is the best treatment for TRS (according to efficacy, effectiveness and well-being); and (3) potential for clozapine to cause vulnerabilities, including potentially lethal adverse drug reactions such as agranulocytosis, pneumonia, and myocarditis. Rational use requires: (1) modification of the clozapine package insert worldwide to include lower doses for Asians and to avoid the lethality associated with pneumonia, (2) the use of clozapine levels for personalizing dosing, and (3) the use of slow and personalized titration. This may make clozapine as safe as possible and contribute to increased life expectancy and well-being. In the absence of data on COVID-19 in clozapine patients, clozapine possibly impairs immunological mechanisms and may increase pneumonia risk in infected patients. Psychiatrists should call their clozapine patients and families and explain to them that if the patient develops fever or flu-like symptoms, the psychiatrist should be called and should consider halving the clozapine dose. If the patient is hospitalized with pneumonia, the treating physician needs to assess for symptoms of clozapine intoxication since halving the dose may not be enough for all patients; consider decreasing it to one-third or even stopping it. Once the signs of inflammation and fever have disappeared, the clozapine dose can be slowly increased to the prior dosage level.

Do Asian Patients Require Only Half of the Clozapine Dose Prescribed for Caucasians? A Critical Overview

Since 1997, studies have found that Asians need lower clozapine doses than Caucasians. Caucasians with average clozapine metabolism may need from 300 to 600 mg/day to reach the therapeutic range (350 ng/ml). Thus, serum clozapine concentration-to-dose (C/D) ratios typically range between 0.60 (male smokers) and 1.20 (female non-smokers). A 2019 systematic review of clozapine levels demonstrated weighted mean C/D ratios of 1.57 in 876 East Asians and 1.07 in 1147 Caucasians (P < .001). In Asian countries, average clozapine doses are lower than 300 mg/day. After sex and smoking stratification in 5 Asian samples with clozapine concentrations, the clozapine dose required to reach 350 ng/ml in female non-smokers ranged from 145 to 189 mg/day and in male smokers, from 259 to 294 mg/day. Thus, in Asian patients with average metabolism (with no inducers other than smoking, with no inhibitors, and in the absence of extreme obesity), the dose needed for clinical response may range between 150 mg/day for female non-smokers to 300 mg/day for male smokers. Clozapine levels may help personalize dosing in clozapine poor metabolizers (PMs) and ultrarapid metabolizers (UMs). Asian PMs may need very low doses (50-150 mg/day) to obtain therapeutic concentrations. About 10% (range 2-13%) of Asians are genetic PM cases. Other PMs are patients taking CYP1A2 inhibitors such as fluvoxamine, oral contraceptives, and valproate. Temporary clozapine PM status may occur during severe systemic infections/inflammations with fever and C-reactive protein (CRP) elevations. Asian UMs include patients taking potent inducers such as phenytoin, and rarely, valproate.