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At least 19 recordsLinked to original sources

PubMed2000

Effects of fixed low-dose warfarin, aspirin-warfarin combination therapy, and dose-adjusted warfarin on thrombogenesis in chronic atrial fibrillation.

BACKGROUND AND PURPOSE: Recent clinical trials have established that adjusted-dose warfarin (international normalized ratio [INR] 2.0 to 3.0) is highly effective in the reduction of ischemic stroke in patients with nonvalvular atrial fibrillation (AF). We hypothesized that the introduction of fixed low-dose warfarin alone or in combination with aspirin (300 mg) could normalize hemostatic markers, namely plasma fibrin D-dimer (an index of thrombogenesis), plasminogen activator inhibitor-1 (PAI-1, an index of fibrinolysis), fibrinogen, and von Willebrand factor (vWf, an index of endothelial dysfunction), in a manner comparable to adjusted-dose warfarin (target INR 2.0 to 3.0). METJODS: Sixty-one patients with AF (44 men, mean+/-SD age 64+/-19 years) who were not receiving any antithrombotic therapy were prospectively randomized into 1 of 3 treatment groups: warfarin (2 mg) (n=23; group 1), combination 1 mg warfarin plus 300 mg aspirin (n=21; group 2) or combination 2 mg warfarin plus 300 mg aspirin (n=17; group 3). Subjects from all 3 AF groups were matched for sex, age, and blood pressure. Blood samples were taken for sequential measurements for changes in plasma fibrin D-dimer, PAI-1, fibrinogen, and vWf before and at 2 and 8 weeks after randomization (phase 1). All patients were subsequently offered adjusted-dose warfarin therapy (phase 2), and an additional blood sample was taken 6 weeks later. RESULTS: When pretreatment results were compared with those from 60 age- and sex-matched healthy control subjects in sinus rhythm, there were significant elevations in levels of fibrinogen (P=0.025), vWf (P<0.0001), and fibrin D-dimer (P<0.0001) in patients with AF compared with control subjects. There were no significant changes in the levels of various indices measured after 2 and 8 weeks of therapy in all 3 groups, except for an increase in PAI-1 level (P=0.024) in group 3. After 6 weeks of therapy with dose-adjusted warfarin (INR 2.0 to 3.0), there was a significant decrease in plasma fibrinogen (P=0.023) and fibrin D-dimer (P=0.0067) levels. There were no significant changes in the levels of PAI-1 (P=0.198) or vWf (P=0.33). CONCLUSIONS: The present results confirmed that high levels of vWf, fibrinogen, and fibrin D-dimer levels were present in patients with AF compared with control subjects. Moreover, the introduction of 300 mg aspirin plus low-dose warfarin (1 mg/d), low-dose warfarin alone (2 mg/d), or 300 mg aspirin plus low-dose warfarin (2 mg/d) did not significantly reduce any of the hemostatic markers studied (except PAI-1 levels), whereas conventional full-dose warfarin (INR 2.0 to 3.0) significantly reduced levels of fibrin D-dimer and fibrinogen. These results are in keeping with the disappointing ineffectiveness of low-intensity warfarin therapy, aspirin-warfarin combination, and ultralow-dose warfarin therapy in the recent prematurely terminated clinical trials and the established benefits of conventional adjusted-dose anticoagulation therapy.

Aged↗

PubMed1979

Plasma quantitation of warfarin and warfarin alcohol by gas chromatography chemical ionization mass spectrometry in patients on warfarin maintenance therapy.

A quantitative method has been developed to measure plasma concentrations of warfarin and warfarin alcohol. The analytical procedure uses deuterated analogues as internal standards, and the technique of selected ion monitoring following gas chromatography methane chemical ionization mass spectrometry of the 4'-methyl ethers of warfarin and warfarin alcohol. Concentrations of warfarin and warfarin alcohol have been measured in plasma samples from 43 patients maintained on chronic warfarin therapy and compared with the 'apparent warfarin' concentration as measured by a fluorometric procedure. The study demonstrated a high degree of correlation between the gas chromatography mass spectrometric derived sum of the individual concentrations of warfarin and warfarin alcohol, and the 'apparent warfarin' concentration determined from a spectrofluorometric assay.

Chromatography, Gas↗

PubMed2000

Can warfarin randomized trials be reproduced in 'real life'? Adherence to warfarin guidelines for intensity of anticoagulation in a university-based warfarin clinic.

BACKGROUND: Subjects in clinical trials may benefit from the increased attention and specific focus of the trial, thereby limiting the external validity of clinical trial results to clinical practice. Our study evaluated adherence to guidelines for intensity of anticoagulation in a large, university-based warfarin clinic to assess the generalizability of randomized clinical trials of warfarin efficacy to clinical practice. METHODS: We reviewed anticoagulation clinic records of 480 patients observed for up to 2 years to determine the amount of time anticoagulation was within the recommended therapeutic range. RESULTS: The most common indication for warfarin use was atrial arrhythmia (51.5%). Overall, anticoagulation was within the intended international normalized ratio (INR) target range on 57.8% of treatment days. Nontherapeutic treatment days were due more commonly to subtherapeutic INR values (27.6+/-25.7%) than supratherapeutic INR values (14.9+/-17.0%). This pattern was seen across all warfarin indications. CONCLUSION: These data are comparable to those reported from large randomized trials and thus support the generalizability of clinical trials of long-term warfarin anticoagulation to clinical practice.

Adolescent↗

PubMed1994

Disposition of warfarin enantiomers and metabolites in patients during multiple dosing with rac-warfarin.

1. The disposition of warfarin enantiomers and metabolites has been studied in 36 patients receiving chronic rac-warfarin therapy, titrated to approximately the same anticoagulant response. 2. A stereoselective h.p.l.c. assay was employed to determine the concentrations of (R)- and (S)-warfarin, (R,S)-warfarin alcohol and (S)-7-hydroxywarfarin in plasma and 24 h urine samples. The concentrations of (R)-7-hydroxywarfarin, (S,S)-warfarin alcohol and (R)-6- and (S)-6-hydroxywarfarin were also determined in urine samples. The fractions unbound of warfarin enantiomers were determined using equilibrium dialysis. 3. Wide variability was observed in daily dose requirements (mean 6.1 mg; range: 2.5-12 mg), in plasma concentrations of (S)-warfarin (0.48 mg l(-1); 0.11-1.02 mg l(-1)), (R)-warfarin (0.87 mg l(-1); 0.29-1.82 mg l(-1)), (R,S)-warfarin alcohol (0.31 mg l(-1); 0.02-0.72 mg l(-1)) and (S)-7-hydroxywarfarin (0.25 mg l(-1); 0.07-0.37 mg l(-1)) and the percentage unbound of (S)-warfarin (0.53%; 0.29%-0.82%) and (R)-warfarin (0.54%; 0.26%-0.96%). 4. The mean plasma clearances of warfarin enantiomers were 7.5 1 day-1 per 70 kg (2.5-22.1) for (S)-warfarin and 3.6 1 day-1 per 70 kg (1.6-8.8) for (R)-warfarin. There was a significant correlation between the estimated formation clearance of (S)-7-hydroxywarfarin and the clearance of (S)-warfarin, which accounted for much of the variability in the latter.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

Hepatic microsomal warfarin metabolism in warfarin-resistant and susceptible mouse strains: influence of pretreatment with cytochrome P-450 inducers.

In the present paper, the heterogeneity of hepatic cytochrome P-450 isoenzymes in the mouse has been probed, using warfarin as the substrate. Both sex and strain differences in the in vitro microsomal metabolism of warfarin have been investigated in male and female warfarin-resistant HC and warfarin-susceptible LAC-grey mouse strains. Animals were either untreated or treated with the cytochrome P-450 inducers phenobarbitone, beta-napthoflavone or clofibrate. In both sexes and strains of mice, metabolism of warfarin was stereoselective in favour of the R(+) enantiomer. However, regioselectively was different in both strains and sexes of untreated animals. After pretreatment with phenobarbitone, increases in the rate of formation of 4' and 7-hydroxy R(+) and S(-) warfarin metabolites in HC mice were observed, compared with untreated animals. In LAC-grey mice increases in 4'-, 6-, 7- and 8-hydroxy R(+) and S(-) warfarin metabolites were noted, compared with untreated animals. This data indicated that different amounts or forms of cytochrome P-450s were responsible for warfarin metabolism after phenobarbitone treatment in the two strains. Pretreatment of animals with beta-napthoflavone resulted in significant decreases in the rat of R(+) warfarin metabolism in both strains and sexes of mice indicating that the beta-naphthoflavone-inducible cytochrome P-450 isoenzymes were less active in the metabolism of warfarin, as compared to the uninduced isoenzymes. In addition, the cytochrome P-450 isoenzyme composition in the two mouse strains was different after clofibrate pretreatment, as reflected in reduced levels of some warfarin metabolites and a reduced total metabolism of warfarin, consistent with the narrow substrate specificity of clofibrate-induced cytochrome P450IVA1 for fatty acid hydroxylation. Accordingly, it is clear that both the basal and xenobiotic inducible hepatic cytochrome P-450 isoenzymes in warfarin-resistant and susceptible mice are different and therefore have implications for the in vivo disposition of warfarin.

Animals↗

PubMed1997

Warfarin analog inhibition of human CYP2C9-catalyzed S-warfarin 7-hydroxylation.

Human metabolism of the S-warfarin enantiomer is catalyzed primarily by cytochrome P4502C9 (CYP2C9), which, because of the enzyme's broad drug substrate specificity, leads to drug-S-warfarin interactions. Several warfarin analogs have been synthesized and used to determine whether they exhibit diminished interactions with CYP2C9. The kinetics of the warfarin analogs' inhibition of human liver microsomal CYP2C9 catalyzed metabolism of S-warfarin to S-7-hydroxywarfarin have been investigated. R- and S-7-fluorowarfarin were both predominantly competitive inhibitors, whereas racemic 6-fluorowarfarin and racemic 6,7,8-trifluorowarfarin were predominantly mixed inhibitors with some competitive inhibition. For the alcohols produced by reductive methylation of the side chain of R- and S-warfarin, the R-enantiomer did not inhibit S-warfarin metabolism, whereas the S-enantiomer was primarily a competitive inhibitor. The fluorine substituted warfarins and the S-warfarin alcohol apparently bind with high affinity to CYP2C9. Thus their use clinically (if efficacious) would not prevent CYP2C9 associated warfarin-drug interactions. The R-warfarin alcohol did not inhibit CYP2C9 catalyzed metabolism of S-warfarin and is less likely than warfarin to participate in CYP2C9 associated warfarin-drug interactions.

Aryl Hydrocarbon Hydroxylases↗

PubMed2001

Effects of oral vitamin K on S- and R-warfarin pharmacokinetics and pharmacodynamics: enhanced safety of warfarin as a CYP2C9 probe.

Evidence for the selectivity of S-warfarin metabolism by CYP2C9 is substantial, suggesting that warfarin may be a potential CYP2C9 phenotyping probe. It is, however, limited by its ability to elevate the international normalized ratio (INR) and potentially cause bleeding. The effect of vitamin K to attenuate the elevation of INR may enable the safe use of warfarin as a probe. The objective of this study was to investigate the pharmacokinetics and pharmacodynamics of S- and R-warfarin in plasma following the administration of warfarin alone versus warfarin and vitamin K in CYP2C9*1 homozygotes. Healthy adults received, in a randomized crossover fashion in a fasted state, warfarin 10 mg orally or warfarin 10 mg plus vitamin K 10 mg orally. Blood samples were obtained over 5 days during each phase. INR measurements were obtained at baseline and day 2 in each phase. INR, AUC0-infinity, and t1/2 of plasma S- and R-warfarin were examined. Eleven CYP2C9*1 homozygotes (3 men, 8 women) were enrolled. INR at day 2 following warfarin 10 mg was 1.18 +/- 0.19, which differed significantly from baseline (INR = 1.00 +/- 0.05) and warfarin with vitamin K (INR = 1.06 +/- 0.07). INR at baseline was not significantly different from warfarin with vitamin K. t1/2 and AUC0-infinity of both enantiomers did not significantly differ between the phases. It was concluded that INR is apparently attenuated by concomitant administration of a single dose of vitamin K without affecting the pharmacokinetics of either warfarin stereoisomer. Warfarin 10 mg may be safely used as a CYP2C9 probe in *1 homozygotes when given concomitantly with 10 mg of oral vitamin K.

Administration, Oral↗

PubMed1981

Comparative interaction of sulfinpyrazone and phenylbutazone with racemic warfarin: alteration in vivo of free fraction of plasma warfarin.

Sulfinpyrazone and phenylbutazone cause stereoselective alterations in the metabolic clearance of racemic warfarin in man. To determine if these drugs additionally displace warfarin from its binding sites in vivo free fractions of plasma warfarin were measured by equilibrium dialysis. Single doses of racemic warfarin, 1.5 mg/kgb.wt., were administered to eight normal humans. Six subjects received 300 mg orally of phenybutazone daily, beginning 3 days before warfarin and continuing throughout hypoprothrombinemia. Six subjects in separate experiments received 400 mg orally of sulfinpyrazone daily by the same schedule. Free warfarin of every subject's plasma was measure by equilibrium dialysis; trace amounts of [14C] racemic warfarin were added to each sample. The free fraction increased from 1.09% for warfarin alone to 1.46% (34%) during concurrent phenylbutazone (P less than .001). Free warfarin was unaltered by sulfinpyrazone, 1.08%. As the lack of effect of sulfinpyrazone on free warfarin enantiomorphs, the experiments were repeated with them. Sulfinpyrazone had no significant effect on the free fraction of either S-warfarin or R-warfarin. Sulfinpyrazone augmented the hypoprothrombinemia of racemic warfarin by steroselectively altering its metabolic clearance;phenylbutazone additionally displaced albumin-bound warfarin.

Adolescent↗

PubMed1993

High clearance of (S)-warfarin in a warfarin-resistant subject.

A 30 year old black male required a 60 mg daily dose of warfarin to elicit a therapeutic anticoagulant response (normal warfarin dose 2.5-10 mg day-1; maximum 15 mg day-1). Hereditary warfarin resistance was suspected after compliance, diet, concurrent medication and any gastrointestinal disorder were eliminated as contributory causes. The disposition of vitamin K and vitamin K epoxide was examined in the propositus, his two sisters and 13 control black male subjects. Each subject was given an i.v. bolus dose (5 mg) of vitamin K prior to and after 2 weeks of warfarin therapy (5 mg day-1). The oral clearances of (S)- and (R)-warfarin were also measured in each subject during the last day of warfarin therapy. The mean (+/- s.d.) systemic clearance of vitamin K was similar in all subjects before (114 +/- 35 ml min-1) and after (112 +/- 40 ml min-1) warfarin therapy. The mean (+/- s.d.) AUC value for vitamin K epoxide was increased by warfarin treatment (6.5 +/- 5.4 micrograms ml-1 min before and 139 +/- 78 micrograms ml-1 min after) in all subjects. In the propositus, the oral clearance of (S)-warfarin (14.5 ml min-1) and the clearance ratio for (S)/(R)warfarin (2.6) differed by more than 7 standard deviations from the control group (4.3 +/- 1.1 ml min-1 and 1.2 +/- 0.2, respectively). In one sister of the propositus, the stereoselective disposition of warfarin was comparable with that of her brother ((S)-warfarin clearance = 16.2 ml min-1; and (S)/(R)-warfarin clearance ratio = 2.7).

Adult↗

PubMed1998

Fixed minidose warfarin and aspirin alone and in combination vs adjusted-dose warfarin for stroke prevention in atrial fibrillation: Second Copenhagen Atrial Fibrillation, Aspirin, and Anticoagulation Study.

BACKGROUND: Despite the efficacy of warfarin sodium therapy for stroke prevention in atrial fibrillation, many physicians hesitate to prescribe it to elderly patients because of the risk for bleeding complications and because of inconvenience for the patients. METHODS: The Second Copenhagen Atrial Fibrillation, Aspirin, and Anticoagulation Study was a randomized, controlled trial examining the following therapies: warfarin sodium, 1.25 mg/d; warfarin sodium, 1.25 mg/d, plus aspirin, 300 mg/d; and aspirin, 300 mg/d. These were compared with adjusted-dose warfarin therapy (international normalized ratio of prothrombin time [INR], 2.0-3.0). Stroke or a systemic thromboembolic event was the primary outcome event. Transient ischemic attack, acute myocardial infarction, and death were secondary events. Data were handled as survival data, and risk factors were identified using the Cox proportional hazards model. The trial was scheduled for 6 years from May 1, 1993, but due to scientific evidence of inefficiency of low-intensity warfarin plus aspirin therapy from another study, our trial was prematurely terminated on October 2, 1996. RESULTS: We included 677 patients (median age, 74 years). The cumulative primary event rate after 1 year was 5.8% in patients receiving minidose warfarin; 7.2%, warfarin plus aspirin; 3.6%, aspirin; and 2.8%, adjusted-dose warfarin (P = .67). After 3 years, no difference among the groups was seen. Major bleeding events were rare. CONCLUSIONS: Although the difference was insignificant, adjusted-dose warfarin seemed superior to minidose warfarin and to warfarin plus aspirin after 1 year of treatment. The results do not justify a change in the current recommendation of adjusted-dose warfarin (INR, 2.0-3.0) for stroke prevention in atrial fibrillation.

Adult↗

PubMed1985

Mechanism of warfarin potentiation by amiodarone: dose--and concentration--dependent inhibition of warfarin elimination.

Potentiation of the anticoagulant-effect of warfarin by amiodarone was studied in 30 patients. Thirteen received both drugs concurrently, and 17 received warfarin alone and the combination sequentially. Warfarin doses were adjusted to maintain the prothrombin time between 25-30% of control and its kinetics were compared to those in 20 control patients who received warfarin alone. Potentiation occurred in 28/30 patients, presenting as a 35%-65% reduction in the required dose of warfarin, and was correlated with the dose of amiodarone (r = 0.77, p less than 0.01). The free warfarin fraction was not affected by amiodarone (1.8% vs 1.6% in the controls). Warfarin clearance was lower in amiodarone-treated patients than in the controls (1.4 vs 3.1 ml/min, p less than 0.01) with similar plasma concentrations (1.5 vs 1.2 micrograms/ml) despite administration of lower doses (23.3 vs 39 mg/week respectively). The amiodarone concentration was significantly correlated with the warfarin concentrations independent of the effect of amiodarone on the dose of warfarin. Amiodarone hat no effect on prothrombin other than through its actions on the dose and plasma concentration of warfarin. The mechanism of the amiodarone-warfarin interaction is pharmacokinetic through dose - and concentration - dependent inhibition of warfarin elimination.

Adult↗

PubMedDate not supplied

Spectroscopic techniques in the study of protein binding. A fluorescence technique for the evaluation of the albumin binding and displacement of warfarin and warfarin-alcohol.

1. The binding of racemic mixtures of warfarin and warfarin-alcohol to human serum albumin (HSA) is accompanied by an increase in the fluorescence quantum yield of these compounds. This property has been used to measure the characteristics of the binding of warfarin and warfarin-alcohol to HSA at 22 degrees C and 37 degrees C. Within the limits of the technique, no significant differences between the number of binding sites and strength of binding at the tight site at either temperature were observed. 2. The fluorescence of warfarin and warfarin-alcohol was used to label their binding site on HSA and to study the effects of other drugs on their binding. The results indicate that these two molecules are bound to the same site on HSA. 3. The validity of using changes in the fluorescence of warfarin as a measure of its displacement from HSA was investigated. Good correlations were observed between drug-induced decreases in the fluorescence of bound warfarin and displacement as measured by equilibrium dialysis. The displacement of warfarfin, as detected by fluorescence, correlates well with the increase in free warfarin resulting from addition of therapeutic drug concentrations to undiluted human serum. 4. The most potent displacing agents, by all the methods used, were iophenoxic acid, phenylbutazone and oxyphenylbutazone. The first of these is no longer used clinically, but the latter two are and have been reported to cause hypoprothrominaemia by displacing warfarin from HSA. The present study indicates that changes in the fluorescence of warfarin bound to HSA can be used to measure displacement of bound warfarin and to screen drugs that may cause clinically significant interactions by this mechanism.

Alcohols↗

PubMed1999

Pharmacokinetic interaction between warfarin and a uricosuric agent, bucolome: application of In vitro approaches to predicting In vivo reduction of (S)-warfarin clearance.

A uricosuric agent, bucolome, has been shown to intensify the anticoagulant effect of warfarin. The aims of the present study were to clarify its mechanism(s) and to apply in vitro approaches for predicting this potentially life-threatening in vivo interaction. An in vivo study revealed that Japanese patients given warfarin with bucolome (300 mg/day, n = 21) showed a 1.5-fold greater international normalized ratio than those given warfarin alone (n = 34) despite that the former received a 58% smaller warfarin dose than the latter. Enantioselective assays revealed that bucolome increased plasma unbound fractions of (S)- and (R)-warfarin by 2-fold (p <.01), reduced unbound oral clearances of (S)- and (R)-warfarin by 84 (p <.01) and 26% (p <.05), respectively, and inhibited the unbound formation clearance for (S)-warfarin 7-hydroxylation by 89% (p <.01). In contrast, bucolome elicited no appreciable changes in the plasma unbound (S)-warfarin concentration versus the international normalized ratio relationship. In vitro studies with recombinant human cytochrome P-450 2C9 and liver microsomes showed that bucolome was a potent mixed-type inhibitor for (S)-warfarin 7-hydroxylation, with K(i) of 8.2 and 20.2 microM, respectively. An in vitro model incorporating maximum unbound bucolome concentration in the liver estimated as a sum of hepatic artery and portal vein concentrations and in vitro K(i) made an acceptable prediction for bucolome-induced reductions in in vivo total (bound + unbound) oral clearance, unbound oral clearance, and unbound formation clearance for (S)-warfarin. In conclusion, the augmented anticoagulant effect of warfarin by bucolome due to the metabolic inhibition for pharmacologically more potent (S)-warfarin may be predictable from in vitro data.

Adult↗

PubMed2001

Suppression of CYP3A2 mRNA expression in the warfarin-resistant roof rat, Rattus rattus: possible involvement of cytochrome P450 in the warfarin resistance mechanism.

1. The continual use of warfarin as a rodenticide has caused the development of populations of warfarin-resistant roof rat. To study the biochemical mechanism of warfarin resistance, the mRNA expression levels of the major P450 forms in the warfarin-resistant and -susceptible roof rat liver following exposure to warfarin were quantified by competitive RT-PCR. 2. The constitutive levels of CYP2C11 and CYP3A2 mRNAs in the warfarin-resistant and -susceptible roof rat were extremely low compared with those in the STD rat. In response to warfarin administration, the CYP3A2 mRNA level in the warfarin-susceptible rat increased to about 3-fold of that before the treatment, whereas in the warfarin-resistant roof rat, CYP3A2 mRNA remained at a low level. 3. The present results suggest the possibility that reduced synthesis of CYP3A2 mRNA is involved in the warfarin-resistant mechanism in the roof rat.

Animals↗

PubMed1979

Warfarin and warfarin-alcohol levels in anticoagulated patients.

The relationship between dosage, prothrombin ratio, and steady-state plasma concentrations of warfarin and warfarin-alcohol, were determined in 43 patients regularly attending an anticoagulant clinic. The warfarin and warfarin-alcohol concentrations were determined by a gas chromatographic mass spectroscopic (GC/MS) method. A significant correlation was found between the dose and the plasma level of warfarin. There was no significant correlation between the prothrombin ratio and the dose of warfarin, the steady-state plasma levels of warfarin or warfarin-alcohol, or the sum of their plasma concentrations. Measurement of the plasma levels of warfarin and warfarin-alcohol is likely to be of little help clinically other than to detect failure of compliance or malabsorption.

Adult↗

PubMed2001

Effect of ubidecarenone on warfarin anticoagulation and pharmacokinetics of warfarin enantiomers in rats.

Interaction between the antioxidant ubidecarenone and the oral anticoagulant warfarin enantiomers was investigated in rats. The decreased hypoprothrombinemic response, assessed by means of percent changes of prothrombin complex activity and clotting factor VII activity, to warfarin, was observed following oral administration of 1.5 mg/kg racemic warfarin to rats during an 8-day oral regimen (10 mg/kg daily) of ubidecarenone. The antioxidant had no apparent effect on the in vitro rat serum protein binding of warfarin enantiomers. Treatment with ubidecarenone did not affect the absorption and distribution of the S- and R-enantiomers of warfarin, but produced a significant increase in the total serum clearance values of both R- and S-warfarin in rats. This effect was more pronounced with R-warfarin than with S-warfarin. The increased clearance values are attributable to acceleration of certain metabolic pathways and renal excretion of the warfarin enantiomers.

Animals↗

PubMed1997

Effect of fixed minidose warfarin, conventional dose warfarin and aspirin on INR and prothrombin fragment 1 + 2 in patients with atrial fibrillation.

The efficacy of conventional dose adjusted oral anticoagulation for stroke prevention in patients with non-valvular atrial fibrillation is well-documented but not considered ideal as primary antithrombotic treatment in elderly patients. The antithrombotic effect of fixed minidose warfarin 1.25 mg/day alone or in combination with aspirin 300 mg/day, of conventional dose adjusted warfarin (INR 2.0-3.0), and of aspirin 300 mg/day have been investigated in outpatients with chronic nonvalvular atrial fibrillation in the second Copenhagen Atrial Fibrillation, Aspirin and Anticoagulant Therapy Study (AFASAK 2). In order to investigate the effect on the coagulation system of the treatments, the International Normalized Ratio of the prothrombin time (INR) and prothrombin fragment 1 + 2 (F1 + 2) were monitored at baseline and after three months of treatment in 100 patients consecutively included in the trial. At baseline no differences in INR and F1 + 2 between the four treatment groups were present. After three months of therapy the level of INR increased significantly from baseline in patients receiving warfarin in any dose and the level of F1 + 2 decreased significantly by combined minidose warfarin-aspirin and by dose adjusted warfarin. When comparing the changes over time in F1 + 2 (three-month value minus baseline value) during therapy with fixed minidose warfarin, combined minidose warfarin-aspirin and aspirin alone no significant difference between the groups was found. In conclusion, INR was changed by all three warfarin regimens but only dose adjusted warfarin (INR 2.0-3.0) had a marked effect on F1 + 2.

Aged↗

PubMed1997

Warfarin and epistaxis: should warfarin always be discontinued?

The object of this study was to determine whether warfarin could be safely continued in patients with epistaxis if the International Normalized Ratio (INR) was within the suggested therapeutic range. Twenty patients on warfarin treatment were compared with controls, matched for age and sex. Local measures for the control of epistaxis were undertaken appropriately in all the patients. In the warfarin group 17 patients (85%) did not discontinue warfarin as the INR was within the suggested range. There were no additional bleeding complications or failure of epistaxis control due to continuation of warfarin. There was no significant difference in the mean hospital stay between the warfarin and non-warfarin groups. It is concluded that warfarin can be continued safely in patients with epistaxis, in appropriate circumstances, and that the policy of stopping warfarin routinely in all patients with epistaxis should be reconsidered.

Aged↗