Body mass index as a predictor of the outcomes of acute clozapine toxicity: a cross-sectional study

Letter to the FDA Proposing Major Changes in the US Clozapine Package Insert Supported by Clozapine Experts Worldwide. Part I: A Review of the Pharmacokinetic Literature and Proposed Changes

PURPOSE/BACKGROUND

Clozapine was approved in the United States (US) using 1989 regulations and knowledge. After 30 years, many sections of the US package insert (PI) are outdated.

METHODS

We comprehensively reviewed the literature to propose PI updates. We present the information in 2 articles. In Part I, we focus on basic pharmacology based on 407 relevant articles. Part II focuses on clinical aspects and pharmacovigilance.

FINDINGS/RESULTS

Based on more recent expectations of Food and Drug Administration regulations, we reviewed clozapine basic pharmacology including the following: 1) clearance, 2) pharmacokinetics and pharmacodynamics, and 3) monitoring tools. We identified 9 major problems in the basic pharmacological sections of the PI including the following: 1) in vivo studies indicate that clozapine is dependent on CYP1A2 for its metabolism, 2) the minor role of CYP2D6 in clozapine metabolism requires removing the PI recommendation to lower clozapine doses in CYP2D6 poor metabolizers, 3) in nontoxic concentrations CYP3A4 has a minor role in clozapine metabolism and potent CYP3A4 inhibitors lack clinically relevant effects, 4) several drug-drug interactions need to be updated based on recent literature, 5) systemic inflammation may decrease clozapine metabolism and increase the risk of clozapine intoxication, 6) obesity may decrease clozapine metabolism, 7) patients of Asian and Indigenous American ancestry need lower clozapine doses, 8) personalized titration and c-reactive protein monitoring should be considered until prospective studies are available, and 9) the half-life section needs to be modified to acknowledge that single dosing at night is frequent in the US.

IMPLICATIONS/CONCLUSIONS

An improvement in the US clozapine PI may lead to improvement in PIs worldwide.

Clozapine may consistently protect from suicidal behaviors while other antipsychotics may lack a specific protective effect: a comprehensive VigiBase study interpreted in the context of the prior literature

BACKGROUND

In the United States, clozapine was first approved for treatment-resistant schizophrenia and then for suicidality in schizophrenia psychoses. Systematic reviews support clozapine's anti-suicidal effect, but the forensic literature stresses its lethality during overdoses.

RESEARCH DESIGN AND METHODS

Clozapine reports to the international pharmacovigilance database (VigiBase) were analyzed for suicidal ideation, suicide attempts, intentional overdose, and completed suicides from introduction to 1 January 2024. VigiBase uses the information component (IC) as a disproportionality analysis.

RESULTS

The clozapine ICs (range: other antipsychotics) were: 1) suicidal ideation IC = 0.570 with IC025 = 0.454 to IC975 = 0.680 (IC = 3.568 for aripiprazole and 1.729 for risperidone), 2) suicide attempt IC = 1.428 with IC025 = 1.323 to IC975 = 1.529 (IC = 4.150 for quetiapine and 2.968 for risperidone), 3) intentional overdose: IC = 0.995 with IC025 = 0.864 to IC975 = 1.120 (IC = 4.080 for quetiapine and 1.957 for aripiprazole), and 4) completed suicide IC = 1.133 with IC025 = 1.026 to IC975 = 1.235 (IC = 4.648 for quetiapine and 2.160 for risperidone). In summary, all clozapine ICs were significantly lower. We found 2391 clozapine-treated patients on the suicidality spectrum (627 cases with suicidal ideation, 752 with suicide attempt, 488 with intentional overdose, and 731 with completed suicide) but many were taking other antipsychotics. The most frequent reporting countries were the United States, the United Kingdom, and Croatia.

CONCLUSION

This pharmacovigilance study, with all its inherent limitations, provides independent proof, not overlapping with prior literature, that clozapine may have specific strong anti-suicidal effects that do not appear to be present in other antipsychotics. Further VigiBase studies are needed to compare the lethality of an intentional overdose of clozapine (14.3%) with other antipsychotics.