Search

The objective of this study was to investigate the influence of genotypes associated with reduced activity of vitamin K epoxide reductase complex subunit 1 (VKORC1) and cytochrome P450 2C9 (CYP2C9) on anticoagulation with acenocoumarol during the first 6 weeks of treatment. In 1,525 patients from the Rotterdam Study who were started on anticoagulation therapy with acenocoumarol, the presence of VKORC1 1173C>T and CYP2C9*2 and *3 allele variants was determined. The first international normalized ratio (INR) after initial standard dose, risk of overanticoagulation, and mean dosage at the end of the initiation period were compared between genotypes. The initial standard dosage significantly increased the risk of severe overanticoagulation by 85% for each additional VKORC1 T-allele present. At the end of the initiation period, each VKORC1 T-allele present was shown to decrease the required acenocoumarol dosage by 5.1 mg/week, while each CYP2C9 variant allele present reduced the required dosage by 1.8 mg/week. Our conclusion was that an initial standard dosing regimen with acenocoumarol increases the risk of severe overanticoagulation in patients with variant alleles of the VKORC1 and CYP2C9 genes.

Several beta-blockers are metabolized by the polymorphic enzyme cytochrome P450 2D6 (CYP2D6). CYP2D6*4 is the main polymorphism leading to decreased enzyme activity. The clinical significance of impaired elimination of beta-blockers is controversial, and most studies suffer from inclusion of small numbers of poor metabolizers (PMs) of CYP2D6. In this study, the association between CYP2D6*4 and blood pressure or heart rate was examined in 1,533 users of beta-blockers in the Rotterdam Study, a population-based cohort study. In CYP2D6 *4/*4 PMs, the adjusted heart rate in metoprolol users was 8.5 beats/min lower compared with *1/*1 extensive metabolizers (EMs) (P < 0.001), leading to an increased risk of bradycardia in PMs (odds ratio = 3.86; 95% confidence interval 1.68-8.86; P = 0.0014). The diastolic blood pressure in PMs was 5.4 mm Hg lower in users of beta-blockers metabolized by CYP2D6 (P = 0.017) and 4.8 mm Hg lower in metoprolol users (P = 0.045) compared with EMs. PMs are at increased risk of bradycardia.

Sulfonylurea hypoglycemics are mainly metabolized by the cytochrome P450 2C9 (CYP2C9) enzyme. The CYP2C9*2 and *3 polymorphisms encode proteins with less enzymatic activity and are correlated with elevated serum levels of sulfonylurea, as demonstrated in healthy volunteers. In this study, the effect of these variants is described for patients with diabetes mellitus treated with sulfonylurea. Associations between CYP2C9 polymorphisms, prescribed doses of sulfonylurea, and change in glucose levels after the start of sulfonylurea therapy were assessed in all patients with incident diabetes mellitus starting on sulfonylurea therapy in the Rotterdam Study, a population-based cohort study of 7,983 elderly people. In CYP2C9*3 allele carriers using tolbutamide, the prescribed dose was lower compared to patients with the wild-type CYP2C9 genotype. No differences in the prescribed dose were found in tolbutamide users with the CYP2C9*1/*2 or CYP2C9*2/*2 genotype compared to wild-type patients or in patients using other sulfonylurea. In CYP2C9*3 allele carriers, the mean decrease in fasting serum glucose levels after the start of tolbutamide therapy was larger than in patients with the wild-type genotype, although not statistically significant. Patients with diabetes mellitus who are carriers of a CYP2C9*3 allele require lower doses of tolbutamide to regulate their serum glucose levels compared to patients with the wild-type genotype.

Introduction: Cytochrome P450 (CYP) plays a key role in the metabolism of coumarin anticoagulants and nonsteroidal anti-inflammatory drugs (NSAIDs). Because CYP2C9 is a genetically polymorphic enzyme, genetic variability could play an important role in the potential interaction between NSAIDs and coumarins. We investigated whether NSAIDs were associated with overanticoagulation during therapy with coumarins and evaluated the effect of the CYP2C9 polymorphisms on this potential interaction., Methods: We conducted a population-based cohort study among patients of an anticoagulation clinic who were treated with acenocoumarol or phenprocoumon between April 1, 1991, and May 31, 2003, and whose CYP2C9 status was known. Patients were followed up until an international normalized ratio (INR) of 6.0 or greater was reached or until the end of treatment, death, or the end of the study. Proportional hazards regression analysis was used to estimate the risk of an INR of 6.0 or greater in relation to concomitant use of a coumarin anticoagulant and NSAIDs after adjustment for several potentially confounding factors. To study effect modification by CYP2C9 genotype, stratified analyses were performed for wild-type patients and patients with a variant genotype., Results: Of the 973 patients in the cohort, 415 had an INR of 6.0 or greater. Several NSAIDs increased the risk of overanticoagulation. The risk of overanticoagulation was 2.98 (95% confidence interval, 1.09-7.02) in coumarin-treated patients taking NSAIDs with a CYP2C9*2 allele and 10.8 (95% confidence interval, 2.57-34.6) in those with a CYP2C9*3 allele., Conclusions: Several NSAIDs were associated with overanticoagulation. For NSAIDs that are known CYP2C9 substrates, this risk was modified by allelic variants of CYP2C9. More frequent INR monitoring of patients taking NSAIDs is warranted.

Background: Several case reports have associated combined use of coumarins and antifungal agents with overanticoagulation. However, we are not aware of epidemiologic studies that quantify the risk of overanticoagulation caused by antifungal agents. We conducted a follow-up study in a large population-based cohort to investigate the antifungal agents that are associated with overanticoagulation during therapy with coumarins., Methods: All patients in the Rotterdam Study who were treated with acenocoumarol or phenprocoumon in the study period from April 1, 1991, through Dec 31, 1998, and for whom international normalized ratio data were available were followed up until an INR > or =6.0, the end of their treatment, death, or the end of the study period. Proportional hazards regression analysis was used to estimate the risk of an INR > or =6.0 in relation to concomitant use of an oral anticoagulant and antifungal agents, after adjustment for several potentially confounding factors such as age, gender, hepatic dysfunction, malignancies, and heart failure., Results: Of the 1124 patients in the cohort, 351 had an INR > or =6.0. The incidence rate was 6.9 per 10,000 treatment days. Oral miconazole most strongly increased the risk of overanticoagulation with an adjusted relative risk of 36.6 (95% confidence interval [CI], 12.4-108.0)., Conclusions: In this study among outpatients of an anticoagulant clinic who were on a regimen of coumarins, oral miconazole was especially strongly associated with overanticoagulation. Awareness of these drug interactions and more frequent monitoring of INR values during the initial stages of treatment with some antifungal drugs in patients taking coumarins may minimize the risk of bleeding complications. The concurrent use of miconazole and coumarins should be discouraged.