Effect of CYP3A5*3 genotype on exposure and efficacy of quetiapine: A retrospective, cohort study

Background

The involvement of cytochrome P450 3A5 (CYP3A5) in the metabolism of quetiapine has been proposed, though conclusive evidence is lacking. This study aimed to quantitatively assess the impact of CYP3A5 genetic variability on quetiapine exposure in a Chinese patient population.

Methods

Patient data were retrospectively collected from the database of the Mental Health Centre at the First Hospital of Hebei Medical University, covering the period from September 1, 2019, to July 1, 2023. The study included patients genotyped for CYP3A5 who were treated with quetiapine. Inclusion criteria for the analysis of pharmacokinetic parameters, such as serum concentrations of the drug and its metabolites, included oral administration of quetiapine, availability of information on the prescribed daily dose and concomitant medications, and the determination of steady-state blood levels at the time of sampling (after at least 3 days of continuous administration at the same dose). Exclusion criteria comprised polypharmacy with known CYP3A4 inducers or inhibitors, as well as patients with hepatic or renal insufficiency. The primary endpoint was the exposure to quetiapine and N-dealkylquetiapine, measured using dose-corrected concentrations (C/D). The secondary endpoint was the metabolism of quetiapine to N-dealkylquetiapine, assessed by the ratio of metabolite to parent drug concentrations. The third endpoint is the differences in adverse reactions, QTc intervals, and biochemical parameters among patients with different CYP3A5 genotypes.

Result

Based on the inclusion and exclusion criteria, clinical data from 207 patients were ultimately included in the study. Of these, 20 patients had the CYP3A5*1/*1 genotype, 78 had the CYP3A5*1/*3 genotype, and 109 had the CYP3A5*3/*3 genotype. The CYP3A5*3 variant was found to significantly impact the metabolism of quetiapine. The C/D values for both quetiapine and N-dealkyl quetiapine were notably higher in individuals with the *3/*3 genotype compared to those with the *1/*1 and *1/*3 genotypes (P₁ < 0.001 and P₂ = 0.002, respectively). A comparison of the variability in metabolic ratios among different genotype groups revealed no significant difference (P = 0.067). However, a post hoc analysis indicated that the metabolic ratio in poor metabolizers was significantly lower than that in intermediate metabolizers (P = 0.021). The analysis of adverse reaction incidence and QTc intervals among different genotypes showed no statistically significant differences (P = 0.652, P = 0.486). However, comparison of biochemical parameters across different genotype groups revealed that alanine aminotransferase, uric acid, hemoglobin, and gamma-glutamyl transferase levels were significantly higher in patients with the CYP3A5*3/*3 genotype compared to those with the CYP3A5*1/*1 and CYP3A5*1/*3 genotypes.

Conclusion

The results indicated that the genetic polymorphism of CYP3A5*3 significantly influences the metabolism of quetiapine. Specifically, carriers of the CYP3A5*3/*3 genotype exhibited higher blood levels of quetiapine, with a greater likelihood of these levels exceeding the therapeutic range. This finding underscores the need for clinicians to pay special attention to the efficacy and occurrence of adverse reactions when prescribing quetiapine to patients carrying the CYP3A5*3/*3 genotype.