Quantitative Assessment of CYP2C9 Genetic Polymorphisms Effect on the Oral Clearance of S-Warfarin in Healthy Subjects

The Impact of CYP2C9*11 Allelic Variant on the Pharmacokinetics of Phenytoin and (S)-Warfarin

Cytochrome P450 2C9 (CYP2C9) is responsible for the oxidative metabolism of about 15% of commonly used drugs, some of which are characterized by a narrow therapeutic window. CYP2C9 is highly polymorphic, and over 60 alleles have been described. CYP2C9*2 and CYP2C9*3 are the most common polymorphisms among White patients and both are associated with decreased activity. The evidence concerning the functional importance of less frequent variant alleles is scarce. The objective of the current study was to characterize the in vivo activity of CYP2C9 among carriers of CYP2C9*11, one of the "African" alleles and the fourth most common CYP2C9 variant allele among White patients by using two prototype substrates, phenytoin and (S)-warfarin. Single 300-mg phenytoin and 20-mg warfarin doses were given to 150 healthy Ethiopian Jewish participants who were nonsmokers, at least one week apart. (S)-warfarin oral clearance and phenytoin metabolic ratio (PMR) derived from the ratio of 5-(4-hydroxyphenyl)-5-phenylhydantoin in 24-hour urine collection to plasma phenytoin 12 hours (PMR 24/12) or 24 hours (PMR 24/24) post dosing, were used as markers of CYP2C9 activity. PMR 24/12 and PMR 24/24 were reduced by 50% and 62.2%, respectively, among carriers of CYP2C9*1/*11 (n = 13) as compared with carriers of CYP2C9*1/*1 (n = 127) (false discovery rate (FDR) q < 0.001). The respective decrease in (S)-warfarin oral clearance was 52.6% (FDR q < 0.001). In conclusion, the enzyme encoded by CYP2C9*11 is characterized by a more than 50% decrease in the enzymatic activity, resembling the extent of decrease associated with CYP2C9*3 ("no-function allele"). Among patients of African ancestry, CYP2C9*11 genetic analysis should be considered prior to prescribing of narrow therapeutic window drugs such as phenytoin, warfarin, nonsteroidal anti-inflammatory drugs, or siponimod.

Phenytoin Metabolic Ratio, a Marker of CYP2C9 Activity, is Superior to the CYP2C9 Genotype as a Predictor of (S)-Warfarin Clearance

BACKGROUND

CYP2C9 is a member of the cytochrome P450 (CYP) superfamily responsible for the metabolism of 16% of drugs that undergo oxidative metabolism. The activity of CYP2C9 exhibits marked inter-individual variability, which translates into prominent differences in the pharmacokinetics of CYP2C9 substrates, some of which are characterized by a narrow therapeutic window. Genetic polymorphisms in the gene encoding for CYP2C9 account for a fraction of the variability in CYP2C9 activity. The phenytoin metabolic ratio (PMR) is a marker of CYP2C9 activity in vivo, which correlates with CYP2C9 genetic polymorphisms.

OBJECTIVE

The purpose of the current study was to evaluate the ability of the PMR to predict the oral clearance of (S)-warfarin (SWOCL) and its formation clearance towards its CYP2C9-mediated metabolites (SWCLf) [i.e., 6- and 7-hydroxy-(S)-warfarin].

METHODS

The study was conducted in 150 healthy non-smoker subjects (segment 1) and 60 patients treated with warfarin (segment 2). In the first segment, the participants received on two separate occasions a single 300-mg dose of phenytoin and at least 7 days later a single dose of warfarin (5 or 10 mg). The same PMR procedure was performed in the second segment, except that it was performed either before warfarin initiation or after the patients had reached stable anticoagulation. The PMR was derived from the ratio of 5-(4-hydroxyphenyl)-5-phenyl-hydantoin content in a 24-hour urine collection to plasma phenytoin concentration 12- (PMR24/12) or 24- (PMR24/24) post-dosing. In segment 1, SWOCL was calculated from the ratio of (S)-warfarin dose to the warfarin area under the plasma concentration-time curve extrapolated to infinity and the SWCLf from the ratio of urine content of 6- and 7-hydroxy-(S)-warfarin to (S)-warfarin area under the (S)-warfarin plasma concentration-time curve until the last measured timepoint. In segment 2, estimated SWOCL was derived from the ratio of (S)-warfarin dose to the mid-interval plasma concentration of (S)-warfarin.

RESULTS

The PMR, SWOCL, and SWCLf varied significantly between carriers of different CYP2C9 genotypes in both healthy subjects (p < 0.001) and patients (p < 0.005). However, PMR and SWOCL values exhibited substantial intra-genotypic variability. PMR24/12 and PMR24/24 were significantly correlated with SWOCL both in healthy subjects (r = 0.62 and r = 0.67, respectively, p < 0.001) and in patients (r = 0.57 and r = 0.61, respectively, p < 0.001). In a multiple regression model that included all variables that correlated with SWOCL, PMR was the strongest predictor, explaining 44% and 38% of the variability in SWOCL among healthy subjects and patients, respectively, and accounting for 95.7% (44%/46%) and 90.5% (38%/42%) of the total explained variability in SWOCL among healthy subjects and patients, respectively.

CONCLUSIONS

The PMR is the strongest predictor of SWOCL, and as such, it exhibits a significant advantage over the CYP2C9 genotype. The inclusion of PMR in future dosing algorithms of CYP2C9 substrates characterized by a narrow therapeutic window should be encouraged and further investigated.

Main contribution of UGT1A1 and CYP2C9 in the metabolism of UR-1102, a novel agent for the treatment of gout

UR-1102, a novel uricosuric agent for treating gout, has been confirmed to exhibit a pharmacological effect in patients. We clarified its metabolic pathway, estimated the contribution of each metabolic enzyme, and assessed the impact of genetic polymorphisms using human in vitro materials. Glucuronide, sulfate and oxidative metabolites of UR-1102 were detected in human hepatocytes. The intrinsic clearance by glucuronidation or oxidation in human liver microsomes was comparable, but sulfation in the cytosol was much lower, indicating that the rank order of contribution was glucuronidation ≥ oxidation > sulfation. Recombinant UGT1A1 and UGT1A3 showed high glucuronidation of UR-1102. We took advantage of a difference in the inhibitory sensitivity of atazanavir to the UGT isoforms and estimated the fraction metabolised (fm) with UGT1A1 to be 70%. Studies using recombinant CYPs and CYP isoform-specific inhibitors showed that oxidation was mediated exclusively by CYP2C9. The effect of UGT1A1 and CYP2C9 inhibitors on UR-1102 metabolism in hepatocytes did not differ markedly between the wild type and variants.

Effects of Apatinib on the Pharmacokinetics of Nifedipine and Warfarin in Patients with Advanced Solid Tumors

Background and Purpose

Apatinib is a small-molecule tyrosine kinase inhibitor for the treatment of recurrent or progressive advanced-stage gastric adenocarcinoma or gastroesophageal junction cancer. The in vitro inhibition studies suggested that apatinib exerted potent inhibition on CYP3A4 and CYP2C9. To evaluate the potential of apatinib as a perpetrator in CYP450-based drug–drug interactions in vivo, nifedipine and warfarin were, respectively, selected in the present study as the probe substrates of CYP3A4 and CYP2C9 for clinical drug–drug interaction studies. Since hypertension and thrombus are common adverse effects of vascular targeting anticancer agents, nifedipine and warfarin are usually coadministered with apatinib in clinical practice.

Methods

A single-center, open-label, single-arm, and self-controlled trial was conducted in patients with advanced solid tumors. The patients received a single dose of 30 mg nifedipine on Day 1/14 and a single dose of 3 mg warfarin on Day 3/16. On Day 9–21, the subjects received a daily dose of 750 mg apatinib, respectively. The pharmacokinetics of nifedipine and warfarin in the absence or presence of apatinib was, respectively, investigated.

Results

Compared with the single oral administration, coadministration with apatinib contributed to the significant increases of AUC_0–48h and C_max of nifedipine by 83% (90% confidence interval [CI] 1.46–2.31) and 64% (90% CI 1.34–2.01), respectively. Similarly, coadministration with apatinib contributed to the significant increases of AUC_0-t and C_max of S-warfarin by 92% (90% CI 1.68–2.18) and 24% (90% CI 1.10–1.39), respectively.

Conclusion

Concomitant apatinib administration resulted in significant increases in systemic exposure to nifedipine and S-warfarin. Owing to the risk of pharmacokinetic drug–drug interactions based on CYP3A4/CYP2C9 inhibition by apatinib, caution is advised in the concurrent use of apatinib with either CYP2C9 or CYP3A4 substrates.

The Clinical Pharmacokinetics and Pharmacodynamics of Warfarin When Combined with Compound Danshen: A Case Study for Combined Treatment of Coronary Heart Diseases with Atrial Fibrillation

Warfarin is used as anticoagulant and Compound Danshen prescription (CDP) is able to promote blood circulation. The combination might produce a synergic effect for patients of coronary heart diseases (CHDs) with atrial fibrillation (AF). Whether the combination increases the bleeding risk of warfarin is unclear, so the effects of Compound Danshen dripping pill (CDDP) on the pharmacokinetics (PK) and pharmacodynamics (PD) profiles of warfarin was investigated in patients. The dose and blood concentrations of warfarin, the four indicators of blood coagulation, prothrombin time, activated partial thromboplatin time, thrombin time, fibrinogen, and international normalized ratio value were compared when with and without CDDP treatment. The population PK (PPK) and PPK-PD models were established to assess patient demographics, genetic polymorphisms and CDDP as covariates. And the Seattle Angina Questionnaire was used to evaluate clinical efficacy, and the bleeding risk of combination was analyzed. The results indicated that CDDP had little influence on PK and PD profiles of warfarin in most patients and the combination of CCDP and warfarin would be a promising alternative regime for CHD with AF patients. The study was registered on China Clinical Trial Registry with number ChiCTR-ONRC-13003523.