Methotrexate (MTX) is a commonly used drug for the treatment of rheumatoid arthritis (RA), but its effectiveness can vary greatly among patients. Pharmacogenetics, the study of how genetic variations can affect drug response, has the potential to improve the personalized treatment of RA by identifying genetic markers that can predict a patient’s response to MTX. However, the field of MTX pharmacogenetics is still in its early stages and there is a lack of consistency among studies. This study aimed to identify genetic markers associated with MTX efficacy and toxicity in a large sample of RA patients, and to investigate the role of clinical covariates and sex-specific effects. Our results have identified an association of ITPA rs1127354 and ABCB1 rs1045642 with response to MTX, polymorphisms of FPGS rs1544105, GGH rs1800909, and MTHFR genes with disease remission, GGH rs1800909 and MTHFR rs1801131 polymorphisms with all adverse events, and ADA rs244076 and MTHFR rs1801131 and rs1801133, However, clinical covariates were more important factors to consider when building predictive models. These findings highlight the potential of pharmacogenetics to improve personalized treatment of RA, but also emphasize the need for further research to fully understand the complex mechanisms involved.

Background: Fluoxetine, a widely prescribed selective serotonin reuptake inhibitor, exhibits significant interindividual variability in pharmacokinetics, largely attributed to pharmacogenomic factors. Objectives: The study aimed to evaluate the impact of pharmacogenetics and clinical determinants on the dose-normalized fluoxetine/norfluoxetine metabolic ratio in patients undergoing fluoxetine therapy in routine clinical settings. Methods: Genotypes for CYP2D6, CYP2C9, and CYP2C19 genotypes were determined in 47 patients receiving fluoxetine therapy using TaqMan^® assays. Steady-state trough plasma concentrations of fluoxetine and norfluoxetine were measured using validated high-performance liquid chromatography methods. Log₁₀-transformed dose-normalized fluoxetine/norfluoxetine metabolic ratio (logMR) was compared across CYP2D6, CYP2C9, and CYP2C19 genotype-predicted metabolizer groups. Multivariate generalized linear modeling (GLM) was used to evaluate the independent effects of CYP genotypes and clinical covariates on the logMR. Results: The logMR differed significantly among the CYP2D6 genotype-predicted metabolizer groups (p < 0.003). CYP2D6 poor metabolizers exhibited significantly higher logMR than normal metabolizers (p < 0.004). The GLM analysis confirmed that CYP2D6 genotype was the only significant predictor of the logMR independent of all clinical covariates. No significant effects of CYP2C9, CYP2C19 genotypes, or clinical variables on the logMR were observed. Conclusions: These findings highlight CYP2D6 genotype as a key determinant of fluoxetine metabolism during standard treatment. No associations were observed with CYP2C9 or CYP2C19 genotypes or clinical factors.

Background: Recent studies have associated the presence of the CYP2C:TG haplotype with increased metabolism of CYP2C19 substrates such as escitalopram and sertraline, suggesting a potential regulatory interaction between CYP2C18 and CYP2C19. However, this association has not been demonstrated for other CYP2C19 substrates. Objective: This study aims to elucidate the role of the CYP2C:TG haplotype in modulating CYP2C19 activity using the omeprazole metabolic ratio (MR) within a cocktail drug approach, to characterize its distribution and prevalence among Native Mexican populations, and to evaluate its potential impact on CYP2C19 metabolic phenotypes. Materials and Methods: A total of 256 volunteers from various ethnic native groups from Mexico were genotyped for CYP2C19 (*2, *3, *4, *5, *17) and the CYP2C haplotype (rs2860840 and rs11188059). The MR of omeprazole to 5-hydroxyomeprazole was analyzed to determine individual CYP2C19 metabolic phenotypes and assess metabolic capacity. Results: The CYP2C:TG haplotype was the most prevalent (42.77%), followed by CYP2C:CG (35.74%) and CYP2C:TA (21.48%). The CYP2C:TG haplotype was consistently associated with the CYP2C19*1 allele. Significant differences in logMR values were observed between individuals with and without the TG haplotype (p = 0.02). A trend toward increased metabolic activity associated with CYP2C:TG was observed across most CYP2C19 metabolizer groups, except for rapid metabolizers. No significant association was found between molecular ancestry and the presence or functionality of the haplotype. Conclusions: The CYP2C:TG haplotype appears to be associated with increased CYP2C19 activity, warranting further functional validation before clinical implementation.

Background/Objectives: Venlafaxine has been reported to exhibit significant interindividual pharmacokinetic heterogeneity across populations, which has been linked to cytochrome P450 polymorphisms and clinical factors. This study aimed to assess the impact of pharmacogenetic (PGx) and clinical determinants on the dose-normalized venlafaxine/O-desmethylvenlafaxine (ODV) metabolic ratios (MRs) in routine clinical settings in Spain. Methods: 29 adult patients receiving venlafaxine were prospectively recruited through the MedeA PGx Implementation Strategy into clinical practice (Extremadura, Spain). CYP2D6, CYP2C19, and CYP2C9 genotypes were determined using TaqMan^® assays, and CYP2D6 activity scores were assigned based on allele functionality. Steady-state trough plasma concentration of venlafaxine and ODV were measured using a validated high-performance liquid chromatography method. Dose-normalized venlafaxine/ODV MRs were compared across CYP2D6-, CYP2C19-, and CYP2C9-genotype-predicted metabolizer groups. The influence of demographic and clinical variables on dose-normalized venlafaxine/ODV MR was also assessed. Results: Significant variability in dose-normalized venlafaxine/ODV MRs was observed across CYP2D6 (p = 0.019) and CYP2C19 (p = 0.008) metabolizer groups. Among clinical variables, sex was significantly associated with differences in dose-normalized venlafaxine/ODV MR (p = 0.0006). Conclusions: CYP2D6 and CYP2C19 genotypes and sex significantly contribute to variability in venlafaxine metabolism in patients treated in routine clinical settings. These results highlight the value of combining PGx and clinical data with drug plasma concentration measurement to optimize venlafaxine therapy within PGx implementation programs.

The Cytochrome P450 2C19 (CYP2C19) is a key enzyme involved in the metabolism of numerous clinically relevant drugs, including selective serotonin reuptake inhibitors, tricyclic antidepressants, an...