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Warfarin dosing remains challenging due to substantial inter-individual variability, which can lead to unsafe or ineffective therapy with standard dosing. Model-informed precision dosing (MIPD) can help individualize warfarin dosing, requiring the selection of a suitable model. For models developed from clinical data, the dependence on the study design and population raises questions about generalizability. Quantitative system pharmacology (QSP) models promise better extrapolation abilities; however, their complexity and lack of validation on clinical data raise questions about applicability in MIPD. We have previously derived a mechanistic warfarin/international normalized ratio (INR) model from a blood coagulation QSP model. In this article, we evaluated the predictive performance of the warfarin/INR model in the context of MIPD using an external dataset with INR data from patients starting warfarin treatment. We assessed the accuracy and precision of model predictions, benchmarked against an empirically based reference model. Additionally, we evaluated covariate contributions and assessed the predictive performance separately in the more challenging outpatient data. The warfarin/INR model performed comparably to the reference model across various measures despite not being calibrated with warfarin initiation data. Including CYP2C9 and/or VKORC1 genotypes as covariates improved the prediction quality of the warfarin/INR model, even after assimilating 4 days of INR data. The outpatient INR exhibited higher unexplained variability, and predictions slightly exceeded observed values, suggesting that model adjustments might be necessary when transitioning from an inpatient to an outpatient setting. Overall, this research underscores the potential of QSP-derived models for MIPD, offering a complementary approach to empirical model development.

Cytochrome P450 (CYP) system is a critical elimination route to most pharmaceuticals in human, but also prone to drug-drug interactions arising from the fact that concomitantly administered pharmaceuticals inhibit one another\'s CYP metabolism. The most severe form of CYP interactions is irreversible inhibition, which results in permanent inactivation of the critical CYP pathway and is only restored by de novo synthesis of new functional enzymes. In this study, we conceptualize a microfluidic approach to mechanistic CYP inhibition studies using human liver microsomes (HLMs) immobilized onto the walls of a polymer micropillar array. We evaluated the feasibility of these HLM chips for CYP inhibition studies by establishing the stability and the enzyme kinetics for a CYP2C9 model reaction under microfluidic flow and determining the half-maximal inhibitory concentrations (IC50) of three human CYP2C9 inhibitors (sulfaphenazole, tienilic acid, miconazole), including evaluation of their inhibition mechanisms and nonspecific microsomal binding on chip. Overall, the enzyme kinetics of CYP2C9 metabolism on the HLM chip (KM = 127 ± 55 µM) was shown to be similar to that of static HLM incubations (KM = 114 ± 14 µM) and the IC50 values toward CYP2C9 derived from the microfluidic assays (sulfaphenazole 0.38 ± 0.09 µM, tienilic acid 3.4 ± 0.6 µM, miconazole 0.54 ± 0.09 µM) correlated well with those determined using current standard IC50 shift assays. Most importantly, the HLM chip could distinguish between reversible (sulfaphenazole) and irreversible (tienilic acid) enzyme inhibitors in a single, automated experiment, indicating the great potential of the HLM chip to simplify current workflows used in mechanistic CYP inhibition studies. Furthermore, the results suggest that the HLM chip can also identify irreversible enzyme inhibitors, which are not necessarily resulting in a time-dependent inhibition (like suicide inhibitors), but whose inhibition mechanism is based on other kind of covalent or irreversible interaction with the CYP system. With our HLM chip approach, we could identify miconazole as such a compound that nonselectively inhibits the human CYP system with a prolonged, possibly irreversible impact in vitro, even if it is not a time-dependent inhibitor according to the IC50 shift assay.

BACKGROUND: Empirical use of pharmacogenetic test(PGT) is advocated for many drugs, and resource-rich setting hospitals are using the same commonly. The clinical translation of pharmacogenetic tests in terms of cost and clinical utility is yet to be examined in hospitals of low middle income countries (LMICs).
OBJECTIVE: The present study assessed the clinical utility of PGT by comparing the pharmacogenetically(PGT) guided- versus standard of care(SOC)- warfarin therapy, including the health economics of the two warfarin therapies.
METHODS: An open-label, randomized, controlled clinical trial recruited warfarin-receiving patients in pharmacogenetically(PGT) guided- versus standard of care(SOC)- study arms. Pharmacogenetic analysis of CYP2C9*2(rs1799853), CYP2C9*3(rs1057910) and VKORC1(rs9923231) was performed for patients recruited to the PGT-guided arm. PT(Prothrombin Time)-INR(international normalized ratio) testing and dose titrations were allowed as per routine clinical practice. The primary endpoint was the percent time spent in the therapeutic INR range(TTR) during the 90-day observation period. Secondary endpoints were time to reach therapeutic INR(TRT), the proportion of adverse events, and economic comparison between two modes of therapy in a Markov model built for the commonest warfarin indication- atrial fibrillation.
RESULTS: The study enrolled 168 patients, 84 in each arm. Per-protocol analysis showed a significantly high median time spent in therapeutic INR in the genotype-guided arm(42.85%; CI 21.4-66.75) as compared to the SOC arm(8.8%; CI 0-27.2)(p < 0.00001). The TRT was less in the PG-guided warfarin dosing group than the standard-of-care dosing warfarin group (17.85 vs. 33.92 days) (p = 0.002). Bleeding and thromboembolic events were similar in the two study groups. Lifetime expenditure was ₹1,26,830 in the PGT arm compared to ₹1,17,907 in the SOC arm. The QALY gain did not differ in the two groups(3.9 vs. 3.65). Compared to SOC, the incremental cost-utility ratio was ₹35,962 per QALY gain with PGT test opting. In deterministic and probabilistic sensitivity analysis, the base case results were found to be insensitive to the variation in model parameters. In the cost-effectiveness-acceptability curve analysis, a 90% probability of cost-effectiveness was reached at a willingness-to-pay(WTP) of ₹ 71,630 well below one time GDP threshold of WTP used.
CONCLUSIONS: Clinical efficacy and the cost-effectiveness of the warfarin pharmacogenetic test suggest its routine use as a point of care investigation for patient care in LMICs.

BACKGROUND: Cytochrome P450 (CYP) comprises a group of phase-I metabolizing enzymes that are important in xenobiotics metabolism. Genetic polymorphism of CYPs has been comprehensively studied for their association with a range of diseases. In this study, we assessed single-nucleotide polymorphism (SNP) of CYP1A, CYP1B, CYP2B, and CYP2C and their role in gastrointestinal (GI) cancer susceptibility in the rural population of Maharashtra.
METHODS: In this hospital-based case-control study, the association of polymorphism of CYP genes was studied by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. The study subjects included 200 clinically confirmed GI cancer patients and equal number of healthy controls. Odds ratio (OR) with 95% confidence interval (CI) and P value were evaluated to find out the level of association, where P ≤ 0.005 was considered statistically significant.
RESULTS: After the analysis of CYP1A1*2A (rs4646903), CYP1B1*3 (rs1059836), CYP2B6*5 (rs3211371), CYP2C8*2 (rs11572103), CYP2C9*2 (rs1799853), and CYP2C9*3 (rs1057910), we noticed that variant (T) allele of CYP2B6*5 possessed significantly elevated risk (OR = 4.43; 95% CI: 2.20-8.90; P < 0.0001) of GI cancer in studied population. The genotypic distribution of G/C heterozygote allele of CYP1B1*3 (OR = 0.19, 95% CI = 0.12-0.32; P < 0.0001) and homozygous variant C/C allele (OR = 0.24, 95% CI = 0.13-0.45; P < 0.0001) showed a negative association with the development of GI cancer.
CONCLUSIONS: The findings from this study supported that polymorphism of CYP2B6*5gene may be involved in the development of GI cancer. However, other SNPs of CYP1A, CYP1B, and CYP2C genes did not signify the risk for GI cancer in the studied population of rural Maharashtra.

BACKGROUND: Last few decades, multiple studies all over the world revealed the association of genetic polymorphism in cytochrome P450 (CYP) genes with risk of developing different type of cancers, but contradictory outcomes were evidenced in case of cervical cancer (CC) risk. Therefore, the discrepancies in earlier reports influenced us to evaluate the association of CYP1A1*2A rs4646903, CYP1B1*3 rs1056836, CYP2C8*2 rs11572103, CYP2C9*2 rs1799853, CYP2C9*3 rs1057910, and CYP2C19*2 rs4244285 polymorphisms and CC susceptibility in the women of rural population of Maharashtra.
METHODS: In this case-control study, genetic association of the polymorphisms in CYP genes was studied by using polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method. The study was conducted among 350 clinically confirmed CC patients and 350 healthy volunteers in a population of south-western Maharashtra. The odds ratio (OR) with 95% confidence interval (CI) and P value were evaluated to get the level of association where P ≤ 0.005 was considered as statistically significant.
RESULTS: After the analysis of single-nucleotide polymorphism (SNPs) of CYP1A1, CYP1B1, CYP2C8, CYP2C9, and CYP2C19, we noticed that CYP1B1*3 rs1056836 (Leu4326Val) polymorphism possessed a significantly elevated risk (OR = 3.28; 95% CI: 2.18-4.94; P < 0.0001), whereas CYP2C19*2 rs4244285 showed significantly lower risk (OR: 0.53, 95% CI: 0.33-0.85 P < 0.009) of CC in the studied rural population.
CONCLUSIONS: The findings from this study supported that rs1056836 SNP of CYP1B1*3 increase CC development, whereas rs4244285 of CYP2C19*2 lowers the CC risk in the studied population.

Ubiquitous exposure to environmental endocrine disrupting chemicals (EDCs) instigates a major public health problem, but much remains unknown on the inter-individual differences in metabolism and excretion of EDCs. To examine this we performed a two-stage genome-wide association study (GWAS) for 24-hour urinary excretions of four parabens, two bisphenols, and nine phthalate metabolites. Results showed five genome-wide significant (p-value < 5x10-8) and replicated single nucleotide polymorphisms (SNPs) representing four independent signals that associated with mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP) and mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP). Three of the four signals were located on chromosome 10 in a locus harboring the cytochrome P450 (CYP) genes CYP2C9, CYP2C58P, and CYP2C19 (rs117529685, pMECPP = 5.38x10-25; rs117033379, pMECPP = 1.96x10-19; rs4918798, pMECPP = 4.01x10-71; rs7895726, pMEHHP = 1.37x10-15, r2 with rs4918798 = 0.93). The other signal was on chromosome 6 close to the solute carrier (SLC) genes SLC17A1, SLC17A3, SLC17A4, and SCGN (rs1359232, pMECPP = 7.6x10-16). These four SNPs explained a substantial part (8.3 % - 9.2 %) of the variance in MECPP in the replication cohort. Bioinformatics analyses supported a likely causal role of CYP2C9 and SLC17A1 in metabolism and excretion of MECPP and MEHHP. Our results provide biological insights into mechanisms of phthalate metabolism and excretion with a likely causal role for CYP2C9 and SLC17A1.

Epilepsy is characterized by repeated seizure activity. Valproate, a commonly used antiepileptic drug, shows large inter-individual variation in plasma valproic levels and causes many adverse drug reactions. Aim: To find the influence of CYP2C9*2 and *3 polymorphisms on valproate-associated adverse drug reactions and plasma valproic acid levels in people with epilepsy. Methods: We recruited 158 people with epilepsy (79 cases and 79 controls) from an epilepsy clinic. Steady-state plasma valproic acid levels were measured using liquid chromatography-mass spectrometry and genotyping of CYP2C9 variants was carried out with helps of RT-PCR. Results: The presence of a mutant heterozygous genotype showed an odds ratio (OR) of 2.82 (95% CI: 1.10-7.24) and the adjusted OR was 5.39 (95% CI: 1.69-17.16). There was no significant difference in steady-state plasma valproate concentration between genotypes. Conclusion: The presence of a mutant heterozygous CYP2C9 genotype possesses five-times the risk of developing adverse drug reactions to valproate in people with epilepsy.

OBJECTIVE: Phenytoin is commonly prescribed to prevent postoperative seizures. Despite the rarity of the CYP2C9 genetic polymorphism, which may result in poor phenytoin metabolism, in the Thai population, the authors report a case of phenytoin toxicity in a patient with poor metabolism administered with a standard dose of phenytoin.
METHODS: A 58-year-old Thai woman presented to the outpatient clinic with a 2-day history of nausea, vomiting, and dizziness. She underwent craniotomy for tumor removal 2 weeks after being diagnosed with tuberculum sellae meningioma. After the surgery, she was prescribed 300 mg of phenytoin daily to prevent seizures. During the physical examination, ataxia, horizontal nystagmus, and cerebellar abnormalities were observed, with an initial serum phenytoin concentration of 58.85 mg/L. The brain imaging results were unremarkable. Omeprazole was the only recognized drug interaction; however, it is highly unlikely to account for this condition. Pharmacogenetic investigation of CYP2C9 revealed a homozygous CYP2C9*3/*3 mutation, which is indicative of suboptimal drug metabolism and can reduce phenytoin metabolism by 50%. This patient was administered repeated dosages of activated charcoal over the course of 2 days. Her symptoms eventually subsided, with the phenytoin levels dropping to 29.51 mg/L.
CONCLUSIONS: In the absence of an overdose history or drug-drug interaction, CYP2C9 polymorphism should be suspected in patients with phenytoin toxicity. In such situations, the phenytoin dosage must be decreased and monitored closely.

Aim: A prospective observational study was conducted to evaluate the feasibility of implementing clinical guidelines for warfarin dosing in black Zimbabwean patients. Methods: CYP2C9*5, CYP2C9*6, CYP2C9*8 and CYP2C9*11 and VKORC1 c. 1639 G>A variations were observed in 62 study patients. Results & Conclusion: Overall, 39/62 (62.90%) participants did not receive a warfarin starting dose as would have been recommended by Clinical Pharmacogenetics Implementation Consortium guidelines. US FDA and Dutch Pharmacogenetics Working Group guidelines are based on CYP2C9*2 and CYP2C9*3 only, hence, unlikely useful in this cohort, where such variants were not detected. Clinical Pharmacogenetics Implementation Consortium guidelines, on the other hand, have a specific recommendation on the African-specific variants CYP2C9*5, CYP2C9*6 and CYP2C9*11, and are hence suitable for implementation in Zimbabwe and would help optimize warfarin doses in patients in the study cohort.