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

Antipsychotic exposure and infection risk in people with schizophrenia spectrum disorders during the COVID-19 pandemic: a Danish nationwide registry study

BACKGROUND

Infection risk and mortality are increased in schizophrenia spectrum disorders, which was corroborated during the COVID-19 pandemic. However, evidence is lacking regarding the additional impact of antipsychotic drugs, and the highly debated safety of clozapine treatment during large-scale infection outbreaks. Therefore, we aimed to investigate risk of COVID-19 and non-COVID respiratory infections during exposure to antipsychotics.

METHODS

We used several nationwide Danish registers (National Prescription Registry, National Hospital Registry, Psychiatric Research Register, Microbiology Database, Vaccination Registry, Cause of Death Registry, and Database for Labour market Research) to investigate all individuals aged 18 years or older with a schizophrenia spectrum disorder (ICD-10: F20-F29) living in Denmark between Jan 1 and March 1, 2020. Antipsychotic exposure groups were defined as prevalent-users and incident-users. The full observation period was March 1, 2020 to Dec 31, 2021. Antipsychotic exposure was defined in a time-varying manner and compared with non-exposure. Risk was calculated for mild infection outcomes (positive SARS-CoV-2 PCR and anti-infective drug prescriptions) and severe infection outcomes (hospitalisation and death) related to COVID-19 and non-COVID-19 respiratory infections. Outcomes were adjusted for demographics, socio-economic factors, and comorbidity.

FINDINGS

Of 85 083 individuals (44 293 men [52·1%] and 40 790 women [47·9%], median age 45·8 years [IQR 31·1-60·2]) with pre-existing schizophrenia spectrum disorders, 30 984 had antipsychotic exposure periods. Ethnicity data were not available. During antipsychotic exposure compared with non-exposed periods, assessing mild infection outcomes, risk of a positive SARS-CoV-2 test was decreased (hazard ratio 0·91 [95% CI 0·85-0·97]) and risk of redeeming an anti-infective drug was not statistically significantly different (1·01 [0·97-1·06]). For severe infection outcomes, COVID-19-related hospitalisation risk was increased (1·28 [1·07-1·52]) although COVID-19-related death was not statistically significantly increased (1·24 [0·82-1·86]). For non-COVID-19 respiratory infections, risk was increased both for hospitalisation (1·61 [1·44-1·79]) and death (1·61 [1·18-2·21]). Specifically, COVID-19 hospitalisation risk was increased in individuals older than 70 years, and non-COVID-19 hospitalisation risk increased in individuals older than 40 years and death risk in age groups of 50-59 years and 70-79 years. Based on homogeneity testing, no apparent excess risk of any outcome was observed with clozapine exposure compared with other antipsychotics.

INTERPRETATION

During antipsychotic exposure compared with unexposed periods, risk of severe infection outcomes increases. It seems reasonable to initiate infection countermeasures, such as pneumococcal vaccination, in people older than 40 years with schizophrenia spectrum disorders, who commence or are treated with antipsychotics. We do not suggest the avoidance of specific antipsychotics but rather adherence to treatment guidelines and a call for increased vigilance regarding this at-risk group.

FUNDING

Mental Health Services of the Capital Region of Denmark.

Population pharmacokinetics of olanzapine in pediatric patients with psychiatric disorders

OBJECTIVE

To develop and validate a population pharmacokinetic (PPK) model of oral olanzapine in pediatric Chinese patients in order to individualize therapy in this population.

METHODS

A total of 897 serum concentrations from 269 pediatric patients taking oral olanzapine (ages 8-17 years) were collected. Demographic parameters, biological characteristics and concomitant medications were investigated as covariates. The data were analyzed using a nonlinear mixed-effects modeling approach. Bootstrapping (1000 runs), normalized prediction distribution error (NPDE), and external validation of 62 patients were employed. Simulations were performed to explore the individualized dosing regimens in various situations.

RESULTS

The one-compartment model with first-order absorption and elimination had an apparent clearance (CL/F) of 10.38 L/h, a distribution volume (V/F) of 9.41 L/kg and an absorption rate constant (Ka) fixed at 0.3 h-1. The equation was CL∕F (L∕h) = 10.38 × (body weight∕60)0.25 ×1.33 (if male) × 0.71 (if co-occurrence of infection) × 0.51 (if co-therapy with fluvoxamine) × 1.27 (if co-therapy with sertraline) × 1.43 (if co-therapy with valproate). The final model had satisfactory stability, robustness, and predictive ability. The results from a simulation suggested the oral olanzapine doses required for male and female pediatric patients weighing between 40 and 60 kg without co-medication were 10-15 mg/day and 7.5-10 mg/day, respectively, and dosage adjustments should be based on sex and body weight; and co-administrated with valproate, sertraline, or fluvoxamine.

CONCLUSION

This model may help individualize optimum dosing of oral olanzapine for pediatric patients.

Therapeutic Drug Monitoring of Olanzapine: Effects of Clinical Factors on Plasma Concentrations in Psychiatric Patients

BACKGROUND

Therapeutic drug monitoring (TDM) is strongly recommended for olanzapine due to its high pharmacokinetic variability. This study aimed to investigate the impact of various clinical factors on olanzapine plasma concentrations in patients with psychiatric disorders.

METHODS

The study used TDM data from the PsyMetab cohort, including 547 daily dose-normalized, steady-state, olanzapine plasma concentrations (C:D ratios) from 248 patients. Both intrinsic factors (eg, sex, age, body weight) and extrinsic factors (eg, smoking status, comedications, hospitalization) were examined. Univariate and multivariable, linear, mixed-effects models were employed, with a stepwise selection procedure based on Akaike information criterion to identify the relevant covariates.

RESULTS

In the multivariable model (based on 440 observations with a complete data set), several significant findings emerged. Olanzapine C:D ratios were significantly lower in smokers (β = -0.65, P < 0.001), valproate users (β = -0.53, P = 0.002), and inpatients (β = -0.20, P = 0.025). Furthermore, the C:D ratios decreased significantly as the time since the last dose increased (β = -0.040, P < 0.001). The male sex had a significant main effect on olanzapine C:D ratios (β = -2.80, P < 0.001), with significant interactions with age (β = 0.025, P < 0.001) and body weight (β = 0.017, P = 0.011). The selected covariates explained 30.3% of the variation in C:D ratios, with smoking status accounting for 7.7% and sex contributing 6.9%. The overall variation explained by both the fixed and random parts of the model was 67.4%. The model facilitated the prediction of olanzapine C:D ratios based on sex, age, and body weight.

CONCLUSIONS

The clinical factors examined in this study, including sex, age, body weight, smoking status, and valproate comedication, remarkably influence olanzapine C:D ratios. Considering these factors, in addition to TDM and the clinical situation, could be important for dose adjustment.

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.

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.

Real-World Effectiveness of High-Dose Olanzapine and Clozapine for Treatment-Resistant Schizophrenia in Japan: A Retrospective Bidirectional Mirror-Image Study

BACKGROUND

Clozapine is considered the gold standard medication for treatment-resistant schizophrenia (TRS). However, given that clozapine treatment is associated with the burden of regular blood monitoring and the risk of life-threatening adverse effects, high-dose olanzapine can serve as an alternative treatment. We conducted a bidirectional mirror-image study to evaluate the effectiveness of high-dose olanzapine compared with clozapine.

METHODS

We included patients with TRS who switched from olanzapine to clozapine or switched from clozapine to olanzapine, and received high-dose (>20 mg/d) olanzapine treatment for ≥4 weeks at Yamanashi Prefectural Kita Hospital. We obtained data on hospitalization, seclusion, and modified electroconvulsive therapy (mECT) during the clozapine phase and the olanzapine phase.

RESULTS

A total of 44 patients were included. When patients switched from high-dose olanzapine to clozapine (n = 32), significant reductions were found in the total days of seclusion, the total number of mECT, and the number of patients who received mECT at least once. When patients switched from clozapine to high-dose olanzapine (n = 12), a significant reduction was found in the number of patients who received mECT at least once. When data from both directions of treatment were combined, significant reductions were found in the total days of seclusion, the total number of mECT, and the number of patients who received mECT at least once in favor of clozapine.

CONCLUSIONS

Findings suggest that high-dose olanzapine may not be as effective as clozapine for patients with TRS in real-world practice. However, it should be noted that there are unique circumstances that restrict the use of clozapine in Japan.

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.

Reflections on the Lack of Consideration of Ethnic Ancestry to Stratify Clozapine Dosing

This review article argues against trusting standard clozapine references, including the US package insert, because they do not include advances in the sciences of pharmacokinetics and pharmacovigilance and ignore the effects of ethnic ancestry on therapeutic dosing. The minimum therapeutic dose leading to the minimum therapeutic concentration of 350 ng/mL in serum/plasma can be used to compare individuals/groups with treatment-resistant schizophrenia. The US clozapine package insert recommends targeting doses of 300-450 mg/day and, subsequently, increments of up to 100 mg with a maximum dose of 900 mg/day. Ethnic ancestry is defined by DNA ancestry group. Asians (people with ancestry ranging from Pakistan to Japan) and Indigenous Americans are similar in clozapine dosing; their average clozapine minimum therapeutic dose ranged from 166 mg/day (female non-smokers) to 270 mg/day (male smokers). For those with European ancestry, average clozapine minimum therapeutic doses ranged from 236 mg/day (female non-smokers) to 368 mg/day (male smokers). Based on limited studies, Black (African sub-Saharan ancestry) patients may be treated with typical US doses (300-600 mg/day), assuming no poor metabolism (PM) status. Ancestry's impact on clozapine lethality in four countries is discussed (two countries with highly homogenous populations, Denmark and Japan, and two countries with increasingly heterogenous populations due to immigration, Australia and the UK). An international guideline with 104 authors from 50 countries/regions was recently published, providing 6 personalized clozapine titration schedules for adult inpatients (3 ancestry groups and PM/non-PM schedules) and recommending c-reactive protein monitoring at baseline and weekly for 4 weeks.

Pharmacokinetic Interactions Between Antiseizure and Psychiatric Medications

Antiseizure medications and drugs for psychiatric diseases are frequently used in combination. In this context, pharmacokinetic interactions between these drugs may occur. The vast majority of these interactions are primarily observed at a metabolic level and result from changes in the activity of the cytochrome P450 (CYP). Carbamazepine, phenytoin, and barbiturates induce the oxidative biotransformation and can consequently reduce the plasma concentrations of tricyclic antidepressants, many typical and atypical antipsychotics and some benzodiazepines. Newer antiseizure medications show a lower potential for clinically relevant interactions with drugs for psychiatric disease. The pharmacokinetics of many antiseizure medications is not influenced by antipsychotics and anxiolytics, while some newer antidepressants, namely fluoxetine, fluvoxamine and viloxazine, may inhibit CYP enzymes leading to increased serum concentrations of some antiseizure medications, including phenytoin and carbamazepine. Clinically relevant pharmacokinetic interactions may be anticipated by knowledge of CYP enzymes involved in the biotransformation of individual medications and of the influence of the specific comedication on the activity of these CYP enzymes. As a general rule, these interactions can be managed by careful evaluation of clinical response and, when indicated, individualized dosage adjustments guided by measurement of drugs serum concentrations, especially if pharmacokinetic interactions may cause any change in seizure control or signs of toxicity. Further studies are required to improve predictions of pharmacokinetic interactions between antiseizure medications and drugs for psychiatric diseases providing practical helps for clinicians in the clinical setting.

Effects of Age, Sex, and Comedication on the Plasma Concentrations of Olanzapine in Chinese Patients With Schizophrenia Based on Therapeutic Drug Monitoring Data

BACKGROUND

Olanzapine (OLA) is an atypical second-generation antipsychotic that exhibits significant pharmacokinetic variability. We retrospectively investigated the effects of age, sex, and specific comedications on OLA pharmacokinetics in Chinese patients with schizophrenia.

METHODS

Data on sex, age, and OLA dosage and steady-state plasma concentrations of 386 patients with schizophrenia (who have received OLA or a comedication of OLA with a psychotherapeutic drug) were collected and analyzed. The combined effects of dosage, age, sex, and comedication on OLA plasma levels were assessed via multiple linear regression analyses.

RESULTS

A daily dose of OLA was positively correlated with the drug's plasma concentrations. Overall, the OLA plasma concentrations and concentration-to-dose ratio (C/D) of the studied patients varied by 53.6- and 64.1-fold, achieving median values of 42.7 ng/mL and 2.73 (ng/mL)/(mg/d), respectively. Furthermore, a 1.27-fold higher estimated C/D in patients 60 years or older than in those younger than 60 years was identified. Female patients demonstrated a 33.6% higher C/D than in male patients. When coadministered with mood stabilizers (valproate or lithium), the median OLA C/D was 24.1% to 26.1% lower than that of OLA monotherapy. Interestingly, the OLA plasma concentration and C/D were not significantly affected by a comedication with aripiprazole, haloperidol, amisulpride, risperidone, clozapine, ziprasidone, citalopram, or buspirone.

CONCLUSIONS

The administered drug's dose was identified as an important determinant of the achieved OLA plasma concentration, with a positive correlation. The patients' sex and valproate (or lithium) comedication can significantly affect the C/D of OLA. Therapeutic drug monitoring should be routinely applied in cases of OLA-receiving patients with schizophrenia.

An interpretable stacking ensemble learning framework based on multi-dimensional data for real-time prediction of drug concentration: The example of olanzapine

Background and Aim: Therapeutic drug monitoring (TDM) has evolved over the years as an important tool for personalized medicine. Nevertheless, some limitations are associated with traditional TDM. Emerging data-driven model forecasting [e.g., through machine learning (ML)-based approaches] has been used for individualized therapy. This study proposes an interpretable stacking-based ML framework to predict concentrations in real time after olanzapine (OLZ) treatment.

Methods: The TDM-OLZ dataset, consisting of 2,142 OLZ measurements and 472 features, was formed by collecting electronic health records during the TDM of 927 patients who had received OLZ treatment. We compared the performance of ML algorithms by using 10-fold cross-validation and the mean absolute error (MAE). The optimal subset of features was analyzed by a random forest-based sequential forward feature selection method in the context of the top five heterogeneous regressors as base models to develop a stacked ensemble regressor, which was then optimized via the grid search method. Its predictions were explained by using local interpretable model-agnostic explanations (LIME) and partial dependence plots (PDPs).

Results: A state-of-the-art stacking ensemble learning framework that integrates optimized extra trees, XGBoost, random forest, bagging, and gradient-boosting regressors was developed for nine selected features [i.e., daily dose (OLZ), gender_male, age, valproic acid_yes, ALT, K, BW, MONO#, and time of blood sampling after first administration]. It outperformed other base regressors that were considered, with an MAE of 0.064, R-square value of 0.5355, mean squared error of 0.0089, mean relative error of 13%, and ideal rate (the percentages of predicted TDM within ± 30% of actual TDM) of 63.40%. Predictions at the individual level were illustrated by LIME plots, whereas the global interpretation of associations between features and outcomes was illustrated by PDPs.

Conclusion: This study highlights the feasibility of the real-time estimation of drug concentrations by using stacking-based ML strategies without losing interpretability, thus facilitating model-informed precision dosing.

An international guideline with six personalised titration schedules for preventing myocarditis and pneumonia associated with clozapine

White blood cell (WBC) monitoring has reduced clozapine-treated patient deaths associated with agranulocytosis to a rarity. However, clozapine protocols and package inserts worldwide provide no instructions for preventing myocarditis or pneumonia during clozapine titrations. Prescribers worldwide are largely unaware of that. Meanwhile, as they worry about agranulocytosis, their clozapine-treated patients are at risk of dying from pneumonia or myocarditis. Consequently, an international guideline with 104 authors from 50 countries/regions was recently published to provide personalised clozapine titration schedules for adult inpatients. This forum article reviews pneumonia and myocarditis occurring during clozapine titration, as well as the three most innovative aspects of this new guideline: (1) personalised titration, (2) C reactive protein (CRP) measures, and (3) dose predictions based on blood levels. Clozapine metabolism is influenced by 3 levels of complexity: (1) ancestry groups, (2) sex-smoking subgroups, and (3) presence/absence of poor metabolizer status. These 3 groups of variables should determine the maintenance dose and speed of clozapine titration; they are summarised in a table in the full-text. The international clozapine titration guideline recommends measuring CRP levels simultaneously with WBC, at baseline and weekly at least for the first 4 weeks of titration, the highest risk period for clozapine-induced myocarditis.

Published population pharmacokinetic models of valproic acid in adult patients: a systematic review and external validation in a Chinese sample of inpatients with bipolar disorder

BACKGROUND

This study reviewed all published valproic acid (VPA) population pharmacokinetic (PPK) models in adult patients and assessed them using external validation methods to determine predictive performance.

METHODS

Thirteen published PPK models (labeled with letters A to M) not restricted to children were identified in PubMed, Embase, and Web of Science databases. They were evaluated in a sample totaling 411 serum concentrations from 146 adult inpatients diagnosed with bipolar disorder in a Chinese hospital. Serum concentrations of VPA were analyzed by validated ultra-performance liquid chromatography-tandem mass spectrometry. Performance was assessed by 4 tests (prediction-based diagnostics, visual predictive checks, normalized prediction distribution error, and Bayesian forecasting).

RESULTS

Models K and L, developed in large samples of Chinese and Thai patients, showed good performance in our Chinese dataset. Models H and J demonstrated good performance in Tests 2 and 3 of the 4 tests, respectively. Another 7 models exhibited intermediate performance. The models with the worst performance, F and M, could not be improved by Bayesian forecasting.

CONCLUSION

In our validation study the most important factors contributing to good performance were absence of children, Asian ethnicity, one-compartment models and inclusion of body weight and VPA dose in previously published models.

Precision psychiatry: The complexity of personalizing antipsychotic dosing

Recently, Salagre and Vieta commented on the complexity of implementing precision medicine in psychiatry. For 25 years, this author has focused on a circumscribed type of precision medicine: personalized dosing using pharmacokinetic mechanisms to stratified patients. This short communication focuses on personalized dosing of three oral antipsychotics (clozapine, risperidone and paliperidone) and presents their maintenance dosing in a table which provides dose-correction factors generated by pharmacokinetic studies. Inhibitors need dose-correction factors < 1 and inducers need correction factors >1. Clozapine maintenance dosing is based on the dose needed to reach 350 ng/ml (the minimum plasma therapeutic concentration in treatment-resistant schizophrenia). Clozapine maintenance dosing is influenced by 3 levels of complexity: 1) ancestry groups (Asians/Native Americans; Europeans and Blacks), 2) sex-smoking subgroups (lowest dose in female non-smokers and highest in male smokers) and 3) presence/absence of poor metabolizer status (due to genetic and non-genetic causes including co-prescription of inhibitors, obesity or inflammation). Risperidone and paliperidone maintenance dosing are based on the dose needed to reach plasma concentrations of 20-60 ng/ml. Risperidone PMs need approximately half the dose, which can be explained by genetics (CYP2D6 PMs) or co-prescription of CYP2D6 inhibitors. Fluoxetine co-prescription may require one fourth the risperidone maintenance dose. Carbamazepine co-prescription may require twice the risperidone maintenance dose. Although not well studied, two groups may need higher doses of oral paliperidone: Koreans may need 1.5 times higher doses while those taking carbamazepine may need 3 times higher paliperidone maintenance doses. Precision dosing in psychiatry requires using blood levels of individuals.

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.

Therapeutic Drug Monitoring of Second- and Third-Generation Antipsychotic Drugs-Influence of Smoking Behavior and Inflammation on Pharmacokinetics

Both inflammation and smoking can influence a drug’s pharmacokinetic properties, i.e., its liberation, absorption, distribution, metabolism, and elimination. Depending on, e.g., pharmacogenetics, these changes may alter treatment response or cause serious adverse drug reactions and are thus of clinical relevance. Antipsychotic drugs, used in the treatment of psychosis and schizophrenia, should be closely monitored due to multiple factors (e.g., the narrow therapeutic window of certain psychotropic drugs, the chronicity of most mental illnesses, and the common occurrence of polypharmacotherapy in psychiatry). Therapeutic drug monitoring (TDM) aids with drug titration by enabling the quantification of patients’ drug levels. Recommendations on the use of TDM during treatment with psychotropic drugs are presented in the Consensus Guidelines for Therapeutic Drug Monitoring in Neuropsychopharmacology; however, data on antipsychotic drug levels during inflammation or after changes in smoking behavior—both clinically relevant in psychiatry—that can aid clinical decision making are sparse. The following narrative review provides an overview of relevant literature regarding TDM in psychiatry, particularly in the context of second- and third-generation antipsychotic drugs, inflammation, and smoking behavior. It aims to spread awareness regarding TDM (most pronouncedly of clozapine and olanzapine) as a tool to optimize drug safety and provide patient-tailored treatment.

Therapeutic Drug Monitoring of Second- and Third-Generation Antipsychotic Drugs—Influence of Smoking Behavior and Inflammation on Pharmacokinetics

Both inflammation and smoking can influence a drug’s pharmacokinetic properties, i.e., its liberation, absorption, distribution, metabolism, and elimination. Depending on, e.g., pharmacogenetics, these changes may alter treatment response or cause serious adverse drug reactions and are thus of clinical relevance. Antipsychotic drugs, used in the treatment of psychosis and schizophrenia, should be closely monitored due to multiple factors (e.g., the narrow therapeutic window of certain psychotropic drugs, the chronicity of most mental illnesses, and the common occurrence of polypharmacotherapy in psychiatry). Therapeutic drug monitoring (TDM) aids with drug titration by enabling the quantification of patients’ drug levels. Recommendations on the use of TDM during treatment with psychotropic drugs are presented in the Consensus Guidelines for Therapeutic Drug Monitoring in Neuropsychopharmacology; however, data on antipsychotic drug levels during inflammation or after changes in smoking behavior—both clinically relevant in psychiatry—that can aid clinical decision making are sparse. The following narrative review provides an overview of relevant literature regarding TDM in psychiatry, particularly in the context of second- and third-generation antipsychotic drugs, inflammation, and smoking behavior. It aims to spread awareness regarding TDM (most pronouncedly of clozapine and olanzapine) as a tool to optimize drug safety and provide patient-tailored treatment.

Therapeutic Drug Monitoring of Second- and Third-Generation Antipsychotic Drugs-Influence of Smoking Behavior and Inflammation on Pharmacokinetics

Both inflammation and smoking can influence a drug's pharmacokinetic properties, i.e., its liberation, absorption, distribution, metabolism, and elimination. Depending on, e.g., pharmacogenetics, these changes may alter treatment response or cause serious adverse drug reactions and are thus of clinical relevance. Antipsychotic drugs, used in the treatment of psychosis and schizophrenia, should be closely monitored due to multiple factors (e.g., the narrow therapeutic window of certain psychotropic drugs, the chronicity of most mental illnesses, and the common occurrence of polypharmacotherapy in psychiatry). Therapeutic drug monitoring (TDM) aids with drug titration by enabling the quantification of patients' drug levels. Recommendations on the use of TDM during treatment with psychotropic drugs are presented in the Consensus Guidelines for Therapeutic Drug Monitoring in Neuropsychopharmacology; however, data on antipsychotic drug levels during inflammation or after changes in smoking behavior-both clinically relevant in psychiatry-that can aid clinical decision making are sparse. The following narrative review provides an overview of relevant literature regarding TDM in psychiatry, particularly in the context of second- and third-generation antipsychotic drugs, inflammation, and smoking behavior. It aims to spread awareness regarding TDM (most pronouncedly of clozapine and olanzapine) as a tool to optimize drug safety and provide patient-tailored treatment.