Factors affecting warfarin therapy following cardiac valve surgery

Effect of Early Amiodarone Use on Warfarin Sensitivity, Blood Product Use, and Bleeding in Patients With a Left Ventricular Assist Device

Data are scarce on the effect of amiodarone on warfarin sensitivity and related outcomes after placement of a left ventricular assist device (VAD). This retrospective study compared 30-day outcomes between patients on amiodarone vs no amiodarone after VAD implant. After exclusions, 220 patients received amiodarone and 136 patients did not. Compared to the no amiodarone group, the amiodarone group had a higher warfarin dosing index (0.53 [0.39, 0.79] vs 0.46 [0.34, 0.63]; P = 0.003), incidence of INR ≥ 4 (40.5 vs 23.5%; P = 0.001), incidence of bleeding (24.1 vs 14%; P = 0.021), and use of INR reversal agents (14.5 vs 2.9%, P ≤ 0.001). Amiodarone was associated with bleeding (OR, 1.95; 95% CI, 1.10-3.47; P = 0.022), but not after adjusting for age, estimated glomerular filtration rate, and platelet count (OR, 1.67; 95% CI, 0.92-3.03; P = 0.089). After VAD implant, amiodarone was associated with increased warfarin sensitivity and administration of INR reversal agents.

Impact of genetic and clinical factors on warfarin therapy in patients early after heart valve replacement surgery

PURPOSE

Factors influencing responsiveness to warfarin at treatment onset time were not well identified in Chinese patients undergoing heart valve replacement. We sought to select the most relevant factors that associated with patient response to warfarin early after heart valve surgery.

METHODS

In this observational study, 289 patients starting warfarin therapy early after heart valve replacement surgery were enrolled. CYP2C9 *1, *2, *3, and *5; VKORC1-1639 G>A, CYP4F2 V433M, and GGCX rs11676382 genotypes; clinical characteristics, response to therapy, and bleeding and thrombosis events were collected. The primary outcomes were the time to the first INR equal to or more than lower limit of therapeutic range and the warfarin dose requirements. Stepwise multiple linear regression was performed to develop a dosing algorithm to predict the warfarin dose requirements.

RESULTS

The results of univariate analysis showed lone VKORC1-1639 G>A, CYP2C9 *1/*3, cefazolin, cefoperazone-sulbactam, increased BMI, Δhemoglobin, and white blood cell count could significantly affect patient responsiveness to warfarin in the initial period of anticoagulation. Multivariate analysis resulted in an equation: Accumulated warfarin doses (mg) = 17.068 VKORC1-1639 G>A - 4.261 hypertension + 0.593 BMI - 0.115 age - 4.852 CYP2C9 *1/*3 - 2.617 cefazolin - 4.902 cefoperazone-sulbactam - 4.537, which could explain 40.2% of the variability in warfarin dose needed to reach the first INR equal to or more than lower limit of therapeutic range.

CONCLUSIONS

Both genetic and clinical factors contributed to anticoagulation effect of warfarin in the initial period of treatment. Our findings could provide a basis for the personalized management of warfarin use in the early stage of anticoagulation in northern Chinese patients.

Warfarin-Induced Rapid Rise in INR Post-Cardiac Surgery Is Not Associated With Increased Bleeding Risk

Background: Post-cardiac surgery bleeding can have devastating consequences, and it is unknown if warfarin-induced rapid international normalized ratio (INR) rise during the immediate postoperative period increases bleed risk. Objective: To determine the impact of warfarin-induced rapid-rise INR on post-cardiac surgery bleeding. Methods: This was a single-center, retrospective chart review of post-cardiac surgery patients initiated on warfarin at Mayo Clinic Hospital, Rochester. Patients were grouped based on occurrence or absence of rapid-rise INR (increase ≥1.0 within 24 hours). The primary outcome compared bleed events between groups. Secondary outcomes assessed hospital length of stay (LOS) and identified risk factors associated with bleed events and rapid rise in INR. Results: During the study period, 2342 patients were included, and 56 bleed events were evaluated. Bleed events were similar between rapid-rise (n = 752) and non-rapid-rise (n = 1590) groups in both univariate (hazard ratio [HR] = 1.22; P = 0.594) and multivariable models (HR = 1.24; P = 0.561). Those with rapid-rise INR had longer LOS after warfarin administration (discharge HR = 0.84; P = 0.0002). The most common warfarin dose immediately prior to rapid rise was 5 mg. Risk factors for rapid-rise INR were low body mass index, female gender, and cross-clamp time. Conclusion and Relevance: This represents the first report to assess warfarin-related rapid-rise INR in post-cardiac surgery patients and found correlation to hospital LOS but not bleed events. Conservative warfarin dosing may be warranted until further research can be conducted.

Identification of clinical factors predicting warfarin sensitivity after cardiac surgery

Background

Warfarin is commonly initiated post-cardiac surgery to reduce the risk of intracardiac thrombus formation. Studies have found that sensitivity is increased after cardiac surgery and anticoagulation is subsequently difficult to manage. This study set out to identify clinical markers of increased warfarin sensitivity in patients after cardiac surgery, and build a model that can predict warfarin sensitivity, and improve safety in this setting.

Methods

The study was an observational, retrospective cohort design. Clinical parameters including left ventricular ejection fraction (LVEF), cross-clamp time, age, serum albumin and C-reactive protein concentrations were collected from consenting patients who had undergone cardiac surgery and were prescribed postoperative warfarin. The warfarin dose index (WDI) was calculated for each patient from their international normalized ratio (INR) and warfarin dose, as a measure of sensitivity.

Results

A total of 41 patients were recruited to the study. Logarithmically transformed WDI (log WDI) significantly correlated with LVEF, cardiopulmonary bypass (CPB) time, cross-clamp time, baseline INR and co-administration of amiodarone (p < 0.05). When added to a linear regression model, LVEF and cross-clamp time produced a model that accounted for 41% of the variance in log WDI (R² = 0.41), p = 0.0002). Applying a log WDI cutoff value of -0.349 discriminated between patients who develop an INR > 4 and those who do not, with a sensitivity of 75% and a specificity of 70%.

Conclusions

This single-centre study has highlighted two risk factors for increased warfarin sensitivity post-cardiac surgery. Further research is needed to confirm these findings in a wider, more diverse population, and to validate this model.

Increased Sensitivity to Warfarin After Heart Valve Replacement

Background:

The dosage requirement of warfarin to achieve a given international normalized ratio (INR) often varies considerably between the immediate postoperative period and long-term follow-up in patients with prosthetic heart valves, leading to INR instability.

Objective:

To document the extent of warfarin sensitivity in a prospective study of patients receiving heart valve replacements.

Methods:

Clinical and laboratory data regarding anticoagulation for 111 patients who received warfarin following heart valve replacement were collected during their hospital stay (induction period) and between 1 and 3 months after surgery (follow-up period).

Results:

Mean patient age was 65.39 ± 10.55 years (range 29–85), with 66 men. The mean INR value during the follow-up period was, on average, 0.21 higher than the induction period (2.81 ± 0.5 vs 2.6 ± 0.6; p = 0.007). The mean follow-up warfarin dose was 1.54 mg higher than the mean induction warfarin dose (5.09 ± 2.03 vs 3.55 ± 1.94 mg; p < 0.001). The warfarin dose index, which indicates relative sensitivity of warfarin, decreased from 1.16 to 0.65 (p < 0.001). Although the INR values during the induction and follow-up periods were similar, the dose requirement in the follow-up period was, on average, 43% higher than that of the induction period.

Conclusions:

Immediately after heart valve replacement, patients are more sensitive to warfarin and should receive a lower warfarin dose during the initial phase of oral anticoagulation treatment. This enhanced sensitivity decreases with time. Patients require frequent monitoring and are likely to need an increase in the warfarin dose to avoid insufficient anticoagulation during the early follow-up period.

A Pharmacokinetic Study of the Combined Administration of Amiodarone and Ximelagatran, an Oral Direct Thrombin Inhibitor

The oral direct thrombin inhibitor ximelagatran is being developed for the prevention and treatment of thromboembolism. This single-blind, randomized, placebo-controlled, parallel-group study investigated the potential for the interaction of ximelagatran (36 mg every 12 hours for 8 days, measured as its active form melagatran in blood) and amiodarone (single 600-mg oral dose on day 4) in healthy male subjects (n = 26). For amiodarone + ximelagatran versus amiodarone + placebo, geometric mean ratios (90% confidence intervals for amiodarone AUC(0-120) and C(max) were 0.87 (0.69-1.08) and 0.86 (0.66-1.11), respectively. For desethylamiodarone, the principal metabolite of amiodarone, the corresponding ratios were 1.00 (0.89-1.12) for AUC(0-120) and 0.92 (0.77-1.09) for C(max). The geometric mean ratios (90% confidence intervals) for ximelagatran + amiodarone versus ximelagatran were 1.21 (1.17-1.25) for melagatran AUC(0-12) and 1.23 (1.18-1.28) for melagatran C(max). These confidence intervals were within or only slightly outside the interval, suggesting no interaction (0.8-1.25 for the effect of amiodarone on melagatran and 0.7-1.43 for the effect of melagatran on amiodarone or desethylamiodarone). Amiodarone did not affect the concentration-effect relationship of melagatran on activated partial thromboplastin time. Ximelagatran was well tolerated when coadministered with a single dose of amiodarone. Evaluation of the safety of the combination is needed to confirm that the relatively small pharmacokinetic changes in this study are of no clinical significance.

Warfarin anticoagulation after congenital heart surgery at a large children's hospital

Management of warfarin in pediatric patients remains a clinical challenge. Warfarin may be administered after congenital heart surgery, and the risks of morbidity can be high. Currently, no data exist to describe the initiation of warfarin and the risk factors for morbidity in post-congenital heart surgery patients. This study aimed to characterize the time required to reach anticoagulation for patients administered warfarin therapy after cardiac surgery and to identify and characterize the risk factors for supratherapeutic anticoagulation and adverse events after warfarin initiation. This retrospective study reviewed all patients between 2006 and 2011 who received warfarin anticoagulation after cardiac surgery at our institution. Factors associated with a prolonged time required to reach an international normalized ratio (INR) of 2 and factors related to supratherapeutic anticoagulation (INR ≥ 4) were identified. The inclusion criteria were met by 59 patients. The median time required to reach an INR of at least 2 after initiation of warfarin was 2 days (interquartile range (IQR), 2-4). The only groups that required a significantly longer time to reach an INR of 2 were those with a postoperative delay in initiation of warfarin and those receiving heparin anticoagulation before and during warfarin initiation. Nine patients experienced an INR of 4 or more. However, no thrombotic events occurred, and significant bleeding was uncommon. In the largest reported group of patients undergoing anticoagulation after cardiac surgery, warfarin was well tolerated across all age groups. The median time required to reach an INR of 2 after loading with warfarin was 2 days, and adverse events were uncommon.

Clinical impact of temporary therapy interruptions on anticoagulation control in patients treated with warfarin

This retrospective cohort study was completed to describe the impact of short-term therapy interruptions on anticoagulation control in patients receiving warfarin. Patients seen in a pharmacist-managed anticoagulation clinic were included if they were on a stable warfarin dose and then underwent a planned interruption in therapy. Patients were excluded if phytonadione was administered before the interruption or if medications known to interact with warfarin were altered during the interruption. Data were analyzed for 2 groups: (1) patients with a single interruption in therapy (group 1) and (2) patients with a single interruption in therapy plus patients with an extended interruption in therapy (group 2). The primary endpoint was the change in weekly maintenance warfarin dose from preinterruption to postinterruption. Evaluation of 199 patients resulted in 31 interruptions in group 1 and 34 interruptions in group 2. A change in dose was required in 58% of patients in group 1 and 56% of patients in group 2. The mean absolute change in dose was 2.03 ± 2.79 mg (P < 0.003) in group 1 and 1.96 ± 2.72 mg (P < 0.002) in group 2. For the majority of patients, the dose change represented <10% of their preinterruption weekly dose. Of patients requiring a dose change, 50% required an increase in dose. In conclusion, close follow-up is warranted after a warfarin therapy interruption as dose adjustments will likely be needed to regain anticoagulation control and the direction of this dose change cannot be predicted.

Risk factors for elevated INR values during warfarin therapy in hospitalized pediatric patients

BACKGROUND

There are currently no data describing the incidence of or risk factors for elevated International Normalized Ratio (INR) values in patients receiving warfarin at a tertiary care pediatric hospital. By minimizing risk factors for elevated INR values patient morbidity may be minimized.

PROCEDURES

A 6-year retrospective chart review of inpatient admissions at our institution that received warfarin was performed. Factors for elevated INR values, such as patient demographics, disease state, and medication interactions were reviewed. Patients with an INR value ≥ 0.5 above the upper limit of the goal range were compared to patients without an elevated INR value. A logistic regression analysis was performed to identify independent variables for elevated INR values.

RESULTS

A total of 298 patient admissions (184 patients) met study criteria, and the largest patient population was between 1 and 12 years old (36.9%). The most common indication for warfarin was mitral valve replacement (25.5%). An elevated INR occurred in 20.8% of admissions. Logistic regression analysis identified Asian race, an elevated baseline INR value, warfarin initiation after cardiac surgery, days of inpatient warfarin therapy, and drug interactions with ciprofloxacin and lansoprazole as independent variables for an elevated INR value (P < 0.05). Obesity was significant as an independent variable for a non-elevated INR value (P < 0.05).

CONCLUSIONS

Elevated INR values occur often in patients receiving warfarin while admitted to a tertiary care pediatric facility and modifiable risk factors exist for elevated INR values.

Risk factors of vitamin K antagonist overcoagulation

OBJECTIVES

The aims of this prospective study were to identify, in vitamin K antagonist (VKA)-treated patients, factors associated with INR values: (i) greater than 6.0. and (ii) ranging from 4.0 to 6.0 complicated with bleeding. We also assessed VKA-related morbidity in these patients.

METHODS

During a 6-month period, 3090 consecutive patients were referred to our Department of Internal Medicine, including 412 VKA-treated patients. At admission, the medical records of VKA-treated patients were reviewed for type, duration and indication of VKA therapy, previous medical history of VKA-related hemorrhage, comorbidities and concomitant medications.

RESULTS

Forty of the 412 VKA-treated patients (9.7%) exhibited oral anticoagulant related overcoagulation. VKA overcoagulation was associated with high morbidity, leading to major bleeding in 27.5% of cases; moreover, 12.5% of these patients died, death being mainly due to major bleeding. Under multivariate analysis, significant factors for VKA-related overcoagulation were as follows: previous medical history of VKA therapy-related hemorrhage (P=0.00001) and INR levels over therapeutic range (P=0.0006), chronic liver disease (P=0.03), therapy with amiodarone (P=0.009); in contrast, statin therapy was found to be a protective factor of VKA overcoagulation (P=0.008).

CONCLUSIONS

The knowledge of predictive factors of VKA-related overcoagulation seems of utmost importance to improve patients' management. Our study underlines the fact that the potential of drug interaction should be taken into account when choosing amiodarone for patients receiving VKAs. Interestingly, long-term (>6 month) statin therapy may be a protective factor of VKA overcoagulation. Our findings, therefore, suggest that there may be no need to switch long-term users of VKA and statin to a safer alternative therapy.

Patient Factors That Influence Warfarin Dose Response

Warfarin has long been the mainstay of oral anticoagulation therapy for the treatment and prevention of venous and arterial thrombosis. The narrow therapeutic index of warfarin, and the complex number of factors that influence international normalized ratio (INR) response, makes optimization of warfarin therapy challenging. Determination of the appropriate warfarin dose during initiation and maintenance therapy requires an understanding of patient factors that influence dose response: age, body weight, nutritional status, acute and chronic disease states, and changes in concomitant drug therapy and diet. This review will examine specific clinical factors that can affect the pharmacokinetics and pharmacodynamics of warfarin, as well as the role of pharmacogenetics in optimizing warfarin therapy.

Integration of genetic, clinical, and INR data to refine warfarin dosing

Well-characterized genes that affect warfarin metabolism (cytochrome P450 (CYP) 2C9) and sensitivity (vitamin K epoxide reductase complex 1 (VKORC1)) explain one-third of the variability in therapeutic dose before the international normalized ratio (INR) is measured. To determine genotypic relevance after INR becomes available, we derived clinical and pharmacogenetic refinement algorithms on the basis of INR values (on day 4 or 5 of therapy), clinical factors, and genotype. After adjusting for INR, CYP2C9 and VKORC1 genotypes remained significant predictors (P < 0.001) of warfarin dose. The clinical algorithm had an R(2) of 48% (median absolute error (MAE): 7.0 mg/week) and the pharmacogenetic algorithm had an R(2) of 63% (MAE: 5.5 mg/week) in the derivation set (N = 969). In independent validation sets, the R(2) was 26-43% with the clinical algorithm and 42-58% when genotype was added (P = 0.002). After several days of therapy, a pharmacogenetic algorithm estimates the therapeutic warfarin dose more accurately than one using clinical factors and INR response alone.

CYP2C9 polymorphism and warfarin sensitivity in Taiwan Chinese

BACKGROUND

Warfarin prevents thromboembolism in patients with prosthetic heart valvular replacement. Cytochrome P4502C9 (CYP2C9) is polymorphic in human and is principally responsible for the metabolism of warfarin. However, known CYP2C9 polymorphisms cannot entirely account for the low dose requirement of warfarin in Chinese-Taiwanese receiving mitral valve replacement. We screened a new polymorphism of CYP2C9 and investigated its role in warfarin sensitivity.

METHODS

We examined warfarin dose requirements in 239 Chinese-Taiwanese patients who had attended a cardiac surgery clinic in National Taiwan University Hospital. DNA samples were obtained from 106 Chinese-Taiwanese (37 patients and 69 unrelated healthy controls), and healthy control subjects of Caucasians (n=28) and African-Americans (n=28). Four out of those 37 patients were poor metabolizers of warfarin, and their DNA were subjected to sequencing analysis. Moreover, CYP2C9 genotyping analyses were performed using PCR-RFLP analysis. The chi2 test and Fisher's exact test were used to compare the differences of the allelic frequency and genotype. The association between warfarin dose requirement and genetic polymorphism of CYP2C9 was also analysed.

RESULTS

The mean daily warfarin dose was 3.11+/-1.62 mg for the maintenance of the international normalized ratio of 2 to 3 in 239 patients. A single nucleotide substitution from G to C was found in this study. This SNP, G-65/C, is in intron 3, 65 base pairs upstream of exon 4. The allelic frequencies of C-65 in healthy controls were 0.125, 0.058 and approximately 0 with respect to African-American, Chinese-Taiwanese and Caucasian, implying inter-ethnic variations of the C-65 allele. In addition, patients who were carrier of either the heterozygous or homozygous C-65 variant received half of the usual warfarin dose.

CONCLUSION

The novel intronic G-65/C mutation appears to be inter-racially different in allelic frequency, and that the anticoagulation was affected in response to warfarin sensitivity in Chinese-Taiwanese patients receiving mitral valve replacement.

Warfarin-induced small bowel obstruction

We present a rare case of small bowel obstruction in a patient on long-term anticoagulation. A 53-year woman presented with abdominal pain and vomiting. She was on warfarin following aortic and mitral valve surgery. A small bowel follow through revealed jejunal narrowing consistent with a stricture. This probably was the result of submucosal bleeding because of over warfarinazation. The warfarin was stopped and she started on heparin with complete resolution of symptoms. This rare complication of anticoagulation should be considered in patients on warfarin. Early diagnosis is crucial as most patients are treated conservatively with very few patients requiring surgery.