Evaluating patients' warfarin requirements

Comparing Usual Care With a Warfarin Initiation Protocol After Mechanical Heart Valve Replacement

BACKGROUND

The immediate postoperative warfarin sensitivity for patients receiving heart valve prostheses is increased. Established warfarin initiation protocols may lack clinical applicability, resulting in dosing based on clinical judgment.

OBJECTIVE

To compare current practice for warfarin initiation with a known warfarin initiation protocol, with doses proportionally reduced to account for the increased postoperative sensitivity.

METHODS

We compared the Mechanical Heart Valve Warfarin Initiation Protocol (Protocol group) with current practice (clinical judgment-Empirical group) for patients receiving mechanical heart valves in an observational before-and-after format. End points were the time to achieve a stable therapeutic international normalized ratio (INR), doses held in the first 6 days, and overanticoagulation in the first 6 days.

RESULTS

The Protocol group (n = 37) achieved a stable INR more rapidly than the Empirical group (n = 77; median times 5.1 and 8.7 days, respectively; P = 0.002). Multivariable analysis indicated that the Protocol group (hazard ratio [HR] = 2.22; P = 0.005) and men (HR = 1.76; P = 0.043) more rapidly achieved a stable therapeutic INR. Age, serum albumin, amiodarone, presence of severe heart failure, and surgery type had no impact. Protocol patients had fewer doses held (1.1% vs 10.1%, P < 0.001) and no difference in overanticoagulation (2.7% vs 9.1%, P = 0.27).

CONCLUSION

The Mechanical Heart Valve Warfarin Initiation Protocol provided a reliable approach to initiating warfarin in patients receiving mechanical aortic or mitral valves.

Evaluation of Anticoagulation Therapy in an Academic Nursing Home

Objective:

To evaluate the warfarin management patterns in an academic nursing home and evaluate what predetermined factors are associated with variability in the international normalized ratio (INR).

Setting:

A 566-bed academic nursing home.

Methods:

A retrospective chart review of all residents receiving warfarin therapy for >3 consecutive months in a calendar year was conducted. Data were collected regarding the number of times the INR fluctuated during the follow-up period and the degree of fluctuation between each blood sampling. An INR that changed by 0.5–0.99 between samplings was classified as a small fluctuation; a change >0.99 was defined as a large fluctuation. The sample was divided into 2 groups, easy management and difficult management, based on variability in the INR. The easy-management group consisted of residents who had small fluctuations in the INR and who had INRs outside of the therapeutic range ≤10% of the time. The difficult- management group had large fluctuations in the INR, with the ratio outside of the therapeutic range >10% of the time.

Results:

Thirty-seven patients were taking warfarin (mean ± SD age 71 ± 14 y; mean number of medical illnesses 7.6 ± 3). The mean length of time of warfarin therapy was 10.6 ± 3.2 months. The average dose and INR were 4.0 ± 1.9 mg and 2.0 ± 0.3, respectively. No statistically significant differences were found between age, dose, or INR. For patients who had INR values exceeding the therapeutic range, there was no significant difference between the management groups in length of treatment, age, number of medical illnesses, number of high-risk factors, dose, average monthly INR, number of medication adjustments per year, albumin and creatinine levels, total number of medications, or number of routine medications known to interact with warfarin. The difficult-management group received more medications known to interact with warfarin than the easy-management group. These medications may have caused the INR to increase above the normal range (p = 0.003), as well as producing a large (p = 0.001) or small fluctuation (p = 0.0007) in the INR. Of all the interacting medications, 55% were antibiotics and 28% were analgesics. No statistically significant differences in outcome were seen between groups.

Conclusions:

Results of this study indicate that large variations (>0.99) in the INR may be due to newly prescribed medications that enhance the anticoagulant effect of warfarin. These variations may be minimized by closely monitoring the INR when a drug known to interact with warfarin is prescribed.

Relationship between aging and dosage of warfarin: the current status of warfarin anticoagulant therapy for Japanese outpatients in a department of cardiovascular medicine

BACKGROUND

Oral anticoagulant therapy with warfarin is essential for the optimal prophylaxis of thrombosis and embolism in many vascular disorders whose prevalence is high among elderly patients. Elderly Caucasians show increased sensitivity to oral anticoagulants. Although the Japanese are more sensitive to warfarin therapy than Caucasians, the relationship between age and warfarin dosage in the Japanese has not been investigated in detail. Here, we investigated this relationship in Japanese patients.

METHODS

The subjects comprised 102 outpatients (28-87 years) who showed a stable anticoagulant effect (prothrombin time expressed in terms of the international normalized ratio [PT-INR] between 1.6 and 2.6) following long-term warfarin therapy at the Department of Cardiovascular Medicine, National Hospital Organization Hakodate Hospital. The relationship between age, PT-INR, and daily warfarin dose was retrospectively investigated.

RESULTS

The mean values of the characteristics of all the patients were as follows: age, 70.7 (+/-10.5) years; daily dose of warfarin, 2.68 (+/-0.95)mg; PT-INR, 1.99 (+/-0.24). The PT-INR was not correlated with increasing age. The daily dosage of warfarin and the dosage adjusted according to the PT-INR (dose/PT-INR), wherein the lower values indicate a higher sensitivity to warfarin therapy, were significantly inversely correlated with age. In the high PT-INR (PT-INR>2.1) group, no significant difference was observed between the older and younger patients with regard to any characteristics. Conversely, in the low PT-INR (1.6 ≤ PT-INR ≤ 2.1) group, the dose/PT-INR was significantly reduced in the older patients (≥ 65 years); however, no significant difference was observed in the PT-INR value.

CONCLUSIONS

Both age and the controlled PT-INR value are factors responsible for the increasing sensitivity to warfarin in Japanese patients under optimal anticoagulant therapy. Since elderly Japanese patients with low PT-INR values are especially sensitive to warfarin, greater caution should be exercised while determining the dosage schedule in such patients.

Assessment of an age-adjusted warfarin initiation protocol

OBJECTIVE

To examine the time taken to reach a stable international normalized ratio (INR), as well as the incidence of overanticoagulation of an age-adjusted warfarin initiation protocol.

METHODS

Inpatients and outpatients commencing warfarin therapy at 2 teaching hospitals were dosed according to the age-adjusted protocol. Data were collected prospectively.

MAIN OUTCOME MEASURES

Time to reach a stable INR of 2-3 and the number of patients experiencing an INR > or =4 during the first week of warfarin therapy.

RESULTS

Seventy-three patients were assessed; at the completion of the 4-day titration protocol, 63% had achieved a stable INR. After an additional 2 days of empiric dosage adjustment by the attending physician, 86% of the subjects demonstrated a stable INR. Five patients (7%) experienced an INR > or =4. These patients had a nonsignificant trend toward a lower plasma albumin level compared with other patients (p = 0.057, Student's t-test). The INR-driven dose adjustments on days 3 and 4 of this protocol coped with other variables that have been shown to affect maintenance warfarin dosing. These included weight, gender, pharmacologic factors affecting clearance, and the presence of certain predesignated risk factors.

CONCLUSIONS

The age-adjusted dosing protocol rapidly achieved a stable INR with minimal overanticoagulation. Patients with low serum albumin levels (<3.0 g/dL) may be sensitive to the effects of warfarin during the loading phase.

Increased sensitivity to warfarin in elderly Hispanics

It has been suggested that aging enhances the pharmacologic effect of warfarin, but there is little information about the effects of warfarin in aging minority populations. The authors examine the response of an aging Hispanic population to warfarin. Charts in their anticoagulation clinic were retrospectively examined for the following information: age, sex, weight, duration of anticoagulant therapy, number of medical problems, number of medications, number of minor or major bleeding episodes, prothrombin time, warfarin dose, and international normalized ratio (INR). The dose-adjusted prothrombin time ratio (PTR) and dose-adjusted INR were calculated by dividing the PTR and INR by the mean warfarin dose. Four groups were compared by age: < 50, 50 to 59, 60 to 69, and > or = 70. A total of 243 charts were reviewed: 113 female, 130 male; 90% were Hispanic. The most common indication for anticoagulation was atrial fibrillation. Elderly patients had more medical problems (3.1 vs. 2.4) and took more medications (3.4 vs. 2.4) than younger patients. The dose-adjusted PTR and dose-adjusted INR increased with aging (0.59 vs. 0.38 and 0.85 vs. 0.59, p < .05 ANOVA). In a multiple linear regression analysis, only age remained significantly associated with the anticoagulant effect. These results are consistent with previous reports on the effect of warfarin in aging patients and extend these data to the Hispanic population.

Comparison of an age adjusted warfarin loading protocol with empirical dosing and Fennerty's protocol

AIM

A warfarin loading protocol adjusting doses for age was compared to both Fennerty's protocol (Fenn) and empirical dosing (Emp).

METHODS

Patients beginning warfarin were randomised to receive doses according to either the age adjusted (Age) protocol or Fenn. Data were retrospectively collected for patients who had begun warfarin in the previous six months to represent empirical dosing. The study was performed on inpatients being commenced on warfarin for the first time at two teaching hospitals.

MAIN OUTCOME MEASURES

Endpoints were time to reach a stable, therapeutic International Normalised Ratio (INR) between 2-3, the number of patients experiencing an INR > or =4 in the first week and the number of patients who had a dose held in the first week.

RESULTS

Thirty-five patients were assessed in the Age group, 28 in the Fenn group, and 123 patients for the Emp group. Patients using the Age protocol achieved a stable, therapeutic INR more rapidly than either the Fenn (p=0.003, log rank test) or Emp (p<0.001) group. The Age group had a lower proportion of patients experiencing an INR > or =4 in the first week (p<0.05) as well as a lower proportion having doses held in the first week (p<0.01). There were no differences between Emp and Fenn for any of the endpoints.

CONCLUSION

Adjustment of warfarin loading doses for age exhibits clear superiority over the use of Fenn or Emp. This becomes increasingly important as the average age of patients being warfarinised increases, with the recognition that atrial fibrillation requires anticoagulation. Fenn consistently overdosed elderly patients, especially those aged 80 years and older.

Steady state pharmacokinetics of hydrolysed bopindolol in young and elderly men

Steady-state pharmacokinetic parameters of the new, long-acting beta-adrenoceptor blocker bopindolol have been measured in 17 young and 20 elderly healthy men. The t 1/2 beta and the AUC(0----24 h) of hydrolysed bopindolol (the active metabolite) were both increased (40% and 26%, respectively) in the elderly subjects but tmax, Cmax and CL/f were not altered. However, after adjusting the parameters to allow for the different average body weights of the two groups, Cmax and CL/f became significantly different (+29% and -30%, respectively). AUC(0----24 h) was increased by 41%. The changes of up to 41% in pharmacokinetic parameters were smaller than the alterations of 50-100% usually seen when titrating doses of antihypertensive drugs. The clinical relevance of the effects was not examined, but similar changes have been reported for other beta-blockers which did not appear to be clinically relevant and did not affect the dosage required to treat hypertension.