Warfarin initiation nomograms for venous thromboembolism

Warfarin dosing strategies evolution and its progress in the era of precision medicine, a narrative review

Background For decades, vitamin K antagonists and specifically warfarin, have been the sole agents used orally to manage thromboembolic conditions, including stroke and venous thromboembolism (VTE). Several factors lead to warfarin dose variability, including genetic and non-genetic factors which made warfarin management challenging especially at the initiation phase. To overcome the challenges with warfarin dosing at initiation, strategies other than conventional or fixed dosing were introduced and explored. Aim In this narrative review, we aim to discuss and critique the different dosing strategies for warfarin at initiation with more focus on genotype-guided warfarin dosing and the most recent supporting evidence for and against its use. Method Medline database was searched from 1965 to July 2021. Articles addressing different warfarin dosing methods were screened for inclusion. Results A number of methods exist for warfarin initiation. Studies comparing different dosing methods for initiation yielded conflicting outcomes due to differences in study design, population studied, comparator, and outcomes measured. Conclusions Looking at the big picture, the use of genetic dosing for warfarin initiation can lead to better outcomes. Whether these better outcomes are clinically or economically beneficial remains controversial.

Evaluation of the impact of an integrated care pathway for pulmonary embolism: a quasi-experimental pre-post study

Background

An integrated care pathway (ICP) is intended to improve the management of prevalent resource-consuming, life-threatening diseases. The purpose of this study was to determine whether the quality of patient care improved with the establishment of a dedicated unit for pulmonary embolism (PE).

Methods

A quasi-experimental pre-post study (pre: years 2010–2013; post: 2015–2020; year 2014, “washing” period) of PE patients ≥18 years (January 2010–June 2020). The intervention involved the implementation of an ICP for PE.

Results

The sample was composed of 1,142 patients (510 pre-intervention and 612 post-intervention) without significant differences between the two populations. In the post-intervention period, significant reductions were observed in the median length of hospital stay (LOS) (8 vs. 6 days); time to start of oral anticoagulation therapy (4.5 vs. 3.5 days; P<0.001); and the percentage of patients with high-risk PE in whom recanalization was not contraindicated (66.7% vs. 96%; P=0.009). In-hospital and 30-day mortality decreased, although not significantly (4.5% vs. 2.8%; P=0.188; 6.1% vs. 5.2%; P=0.531, respectively). Multivariate logistic regression analysis showed that the median LOS intervention decreased significantly according to the service where patients were referred to, and with the use of the simplified PESI. During follow-up, lifelong anticoagulation was prescribed to a higher proportion of patients in the post-intervention period (30.7% vs. 69.3%; P<0.001).

Conclusions

Although an ICP for PE does not reduce mortality significantly, it improves the quality of patient care.

Assessment of warfarin algorithms for hospitalized adults: searching for a safe dosing strategy

This study evaluates three warfarin dosing algorithms (Kimmel, Dawson, High Dose ≥ 2.5 mg) for hospitalized older adults. A random selection of 250 patients with overshoots (INR ≥ 5 after 48 h of hospitalization) and 250 patients without overshoots were accessed from a database of 12,107 inpatients ≥ 65 years treated with chronic warfarin during hospitalization between January 1, 2014 and June 30, 2016. Algorithms were retrospectively applied to patients 2 days prior to overshoots in the overshoot group, and 2 days prior to the maximum INR reached after 48 h of hospitalization in the non-overshoot group. Patients were categorized as overdosed or not overdosed and compared using descriptive statistics. Logistic regression modeling determined predictors for overshoots. There was no significant difference between overdose and non-overdose groups for progressing to overshoots by the Kimmel (51.0% vs. 48.7%, p = 0.67) or Dawson (48.5 vs. 57.9%, p = 0.19) algorithms. The Low Dose Group (≤ 2.5 mg) was significantly more likely to experience an overshoot than the High Dose Group (56.6% vs. 45.5%, p = 0.04). The Low Dose Group was more likely to be older (81.4% vs. 71.1%, p = 0.02), female (63.5% vs. 49.8%, p = 0.02), weigh less (71.3 ± 21.9 vs. 79 ± 23.1, p = 0.002), and be prescribed amiodarone (16.6% vs. 8.1%, p = 0.01). While none of the algorithms predicted overshoots in logistic regression modeling, weight over 70 kg and black race remained protective. The High Dose Algorithm revealed that providers appropriately gave lower doses to patients at highest risk for warfarin sensitivity. Future studies are needed to investigate tools for inpatient warfarin dosing in older adults.

A Simple Formula for Predicting the Maintenance Dose of Warfarin with Reference to the Initial Response to Low Dosing at an Outpatient Clinic

Objective The pharmacodynamic effect of warfarin varies among individuals, and its maintenance dose is widely distributed. Although many formulae for predicting the maintenance dose of warfarin have been developed, most of them are complex and not in practical use. Methods and Materials Among 12,738 new patients visiting the Cardiovascular Institute between 2004 and 2009, we identified 127 patients (66.6±8.8 years, 89 men) with atrial fibrillation for whom warfarin was newly started with an initial dose of 2 mg/day and the international normalized ratio (INR) at 1 year after warfarin was started was within the therapeutic range. The prediction models for the maintenance dose were developed by an exponential equation and a first-order equation. Results The initial response of the INR to the dose of 2 mg/day (initial INR) ranged from 1.00-3.24 (mean 1.43), while the maintenance dose of warfarin ranged from 0.5-14 mg (mean 3.8 mg). The maintenance dose showed an exponential correlation to the initial INR: (predicted maintenance dose) =5.522× (initial INR) ^-1.556 (R²=0.795, p<0.001). Excluding the patients with a poor response to the initial dose (initial INR <1.1, n=32) permitted a simple correlation with a first-order approximation: (predicted maintenance dose) =-2.009× (initial INR) +6.172 (R²=0.706, p<0.001). Conclusion We developed a simple formula for predicting the maintenance dose of warfarin using the initial response of the INR to low-dose warfarin.

A Case of Migraine With Aura Resolving on Warfarin But Not on Apixaban

Several case reports have associated anticoagulants such as heparin and vitamin K antagonists with reduced symptoms in migraine, but no data exist for direct acting oral factor Xa inhibitors. We report the case of a 55-year-old female who experienced complete remission of migraine with aura for 12 years while on warfarin, with return of symptoms within 3 weeks of switching to apixaban, and resolution of symptoms once again within days of warfarin resumption. Our case suggests that anticoagulation alone is not sufficient to improve migraine symptoms. Further study of vitamin K-dependent proteins not involved in anticoagulation, such as the relatively novel growth arrest-specific gene 6, may clarify the link between warfarin and migraine symptoms.

Analysis of the first therapeutic-target-achieving time of warfarin therapy and associated factors in patients with pulmonary embolism

The present study aimed to investigate the factors affecting the first therapeutic-target-achieving (TTA) time of warfarin therapy in patients with acute pulmonary embolism (PTE). Between January 2008 and June 2013, patients with PTE confirmed by transpulmonary arterial enhanced computed tomographic pulmonary angiography or pulmonary ventilation perfusion scanning were included in the present study. Data collected included demographic information, history of tobacco and alcohol intake, basic diseases (stable and unstable hypertension, diabetes, heart failure, cancer/cerebral infarction, old myocardial infarction and atrial fibrillation), liver and kidney function, the haemoglobin and platelet count of the blood, international normalized ratio monitoring, warfarin dosage adjustment and medication combinations. Dynamic changes in international normalized ratio, anticoagulant efficacy, and adverse events within 90 days were monitored and analyzed. Univariate analysis demonstrated that the following factors affect the first TTA time: Initial dose, body mass index (BMI), liver function, heart failure, and the administration of levofloxacin, cephalosporins, and blood circulation-activating drugs. Logistic regression analysis revealed that the following were independent factors of the first TTA time: Initial dose, BMI, liver function, heart failure and levofloxacin. Therefore, the results of the present study demonstrated that various factors may affect the first TTA time of warfarin therapy, including the initial dose, BMI, liver function, heart function and concomitant medication.