Effect of age upon the induction and maintenance of anticoagulation with warfarin

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.

Oral Anticoagulation Therapy for Elderly Patients With Atrial Fibrillation

Elderly individuals are prone to nonvalvular atrial fibrillation (AF) with associated risks of arterial thromboembolic disease. Despite definitive guidelines, oral anticoagulant therapy (OAC) is notoriously underutilized in patients with AF. Physicians cite excessive bleeding risk as one reason they omit OAC for their older patients with AF. Improved understanding of the pathophysiology of age-related bleeding may improve risk–benefit assessments for warfarin and newer antithrombotic agents. We reviewed the literature to identify age-related pathophysiological elements that can exacerbate the likelihood of bleeding. In the context of the Hypertension, Abnormal renal/liver function, Stroke, Bleeding history or predisposition, Labile international normalized ratio, Elderly, Drugs/alcohol concomitantly (HAS-BLED) bleeding risk framework, we highlight age-related physiological dynamics that predispose to hemorrhage. The combination of increased age (>65 years) with the other elements of the risk factor stratification model identifies patients with AF who are especially susceptible to OAC-related bleeding, irrespective of the agent used. Empirically adjusting OAC dose relative to these common bleeding risks may help to achieve an improved risk–benefit therapeutic ratio.

Determination of plasma warfarin concentrations in Korean patients and its potential for clinical application

BACKGROUND

Warfarin is a widely used oral anticoagulant with broad within- and between-individual dose requirements. Warfarin concentrations can be monitored by assessing its pharmacologic effects on International Normalized Ratio (INR). However, this approach has not been applied in the routine clinical management of patients receiving warfarin therapy. We performed a plasma warfarin assay using high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) to determine if such an assay can be utilized in routine clinical practice.

METHODS

We included a total of 105 patients with atrial fibrillation, and who were receiving warfarin for more than 1 yr. The plasma concentrations of total warfarin and 7-hydroxywarfarin were determined by HPLC-MS/MS (Waters, UK). We assessed the association between warfarin dose, concentration, and INR as well as the effects of these factors on warfarin concentrations.

RESULTS

The mean maintenance dose of warfarin in 105 patients was 4.1 +/-1.3 mg/day (range, 1.7-8.0 mg/day) and their mean plasma warfarin concentration was 1.3+/-0.5 mg/L. We defined a concentration range of 0.6-2.6 mg/L (corresponding to the 2.5th to 97.5th percentile range of the Plasma warfarin levels in the 74 patients showing INR within target range) as the therapeutic range for warfarin. The correlation of warfarin dose with warfarin concentration (r(2)=0.259, P<0.001) was higher than that with INR (r(2)=0.029, P=0.072).

CONCLUSIONS

There was a significant correlation between warfarin dose and plasma warfarin concentrations in Korean patients with atrial fibrillation. Hence, plasma warfarin monitoring can help determine dose adjustments and improve our understanding of individual patient response to warfarin treatment.

The future prospects of pharmacogenetics in oral anticoagulation therapy

Coumarins are the mainstay of oral anticoagulation for the treatment and prophylaxis of thromboembolic disorders. They have a narrow therapeutic index and regular monitoring is therefore required to avoid serious adverse effects. There is wide interindividual variability in dosage requirements, which makes anticoagulation response unpredictable. Current dosing titrations are haphazard and inconvenient and poor initial control leads to morbidity, and occasional mortality, because of bleeding and further thromboembolism. Recent discoveries have helped to characterize the factors that contribute to the interindividual variability in responses to coumarins. Patient and environmental factors that affect anticoagulation response to coumarins include age, body size, dietary vitamin K status, concurrent disease and drug interactions. More recently, single nucleotide polymorphisms in the 2C9 isoform of cytochrome P450 (CYP2C9) and vitamin K epoxide reductase (VKOR) have been shown to make significant contributions to the variability in coumarin dosage requirements. Polymorphisms in other genes that mediate the actions of coumarins may also contribute to this variability. Racial and cultural differences influence dosage requirements, which can be explained, at least in part, by genetic and dietary factors. Incorporation of genetic and environmental factors could help in the prediction of more individualized loading and maintenance doses for safer anticoagulation therapy.

The effect of hospitalization on oral anticoagulation control: A population-based study

BACKGROUND

For patients taking oral anticoagulants (OAC), the proportion of time spent in the therapeutic range is strongly associated with bleeding and thromboembolic risk. Previous studies examining OAC control may not generalize because the patient population was select or INR capture was incomplete.

OBJECTIVES

Measure OAC control for an entire population of elderly people and determine patient factors associated with OAC control.

PATIENTS

People in Eastern Ontario without valve replacement aged 65 years or greater who were treated with warfarin between 1 September 1999 and 1 September 2000.

DESIGN

Retrospective cohort study using population-based administrative databases. OAC control was measured as the proportion of days in therapeutic range (PDTR), defined as the number days with the INR between 2 and 3 divided by total number of days observation. Linear interpolation was used to determine INR levels between measures. Negative binomial regression was used to identify patient factors independently associated with PDTR. We also determined which factors were associated with proportion of days with a critically low (<1.5) or critically high (>/=5) INR.

RESULTS

7179 people were followed for a total of 3238 years. 15% of people were hospitalized during the study. Overall, PDTR was 59.2% (95% CI 59.1%-59.2%). Independent of all other significant factors, hospitalization was associated with a 15% decrease in the PDTR 15% (rate ratio 0.85, 95% CI 0.83-0.87). Hospitalization was also independently associated with greater proportion of time with a critically low INR (rate ratio 1.68, 95% CI 1.51-1.88) and a critically high INR (1.70, 95% CI 1.38-2.08).

CONCLUSIONS

Elderly people in eastern Ontario taking warfarin were therapeutic 59.2% of the time. Independent of other patient factors, patients who are hospitalized have the greatest risk of poor anticoagulation control. Control for anticoagulated patients who get hospitalized should be reviewed to determine if and how it could be improved.

Management of oral anticoagulant in clinical practice: a retrospective study of 187 patients

Oral anticoagulant (OA) therapy is widely used in elderly patients because of the increase of indications with age (venous thromboembolism and atrial fibrillation). A particularity of France is to administer three different OAs (warfarin and more often fluindione or acenocoumarol). In an attempt to assess the particularities of managing all three OAs in elderly patients in clinical practice, we studied the modalities of anticoagulation of 187 consecutive OA therapy patients (mean age = 74.4 years) hospitalized in an Internal Medicine department (95 patients on OA at admission and 92 patients initiated on OA during hospitalization). Patients aged 75 years or older more often required a low dosage of OA than those aged younger than 75, irrespective of the OA (warfarin and more often fluindione or acenocoumarol). Ambulatory patients aged 75 years or older were more susceptible to receive acenocoumarol than were ambulatory patients younger than 75 years (respectively 30/67 vs 8/28, respectively), whereas fluindione was prescribed at the same frequency in ambulatory patients and hospitalized patients, regardless of age group (> or =75: 32/67; <75: 19/28). In hospitalized patients with OA induction, fluindione was prescribed as often in patients younger than 75 than in patients aged 75 years or older (40/47 vs 35/45, respectively). On admission, international normalized ratio was in the target range in 26 of the 95 patients (27.4%) and was >3 in 51 of the 95 patients (51.6%). OA therapy was stopped during hospitalization in 35 patients (36.8%). In conclusion, we have a picture of the practice of anticoagulation with three different OA therapies. Although it is usually recommended to prescribe long half-time OA therapy (2), it appears that short half-time therapy such as acenocoumarol still represents an important number of OA prescriptions in France, especially in ambulatory and elderly patients. International normalized ratio is not in the target range as often as expected in clinical practice, and elderly patients require specific modalities of OA therapy management, such as half dose initiation, use of long-half-life OA, and close monitoring.

Initiation of warfarin therapy in elderly medical inpatients: a safe and accurate regimen

PURPOSE

Elderly patients are at high risk of over-anticoagulation when treated with warfarin, especially during treatment induction. We developed a simple low-dose regimen for starting warfarin therapy in elderly inpatients. The daily maintenance dosage is predicted from the international normalized ratio (INR) measured the day after the third daily intake of a 4-mg dose. We conducted a prospective multicenter study to evaluate the accuracy and safety of this regimen.

METHODS

We studied 106 elderly (age >or=70 years) inpatients (mean [+/- SD] age, 85 +/- 6 years; range, 71 to 97 years) who had a target INR of 2.0 to 3.0. Accuracy in predicting the daily maintenance dose from INR value on day 3 was evaluated.

RESULTS

The predicted daily maintenance warfarin dose (3.1 +/- 1.6 mg/d) correlated closely with the actual maintenance dose (3.2 +/- 1.7 mg/d; R(2) = 0.84). The predicted dose was equal to the actual dose in 77 patients (73%; 95% confidence interval [CI]: 64% to 81%) and within 1 mg in 101 patients (95%; 95% CI: 91% to 99%). The mean time needed to achieve a therapeutic INR was 6.7 +/- 3.3 days (median, 6.0 days); the mean time needed to achieve the maintenance dose was 9.2 +/- 4.5 days (median, 7.0 days). None of the patients had an INR >4.0 during this period. One fatal bleeding event was recorded in a patient with an INR in the therapeutic range.

CONCLUSION

Our warfarin induction regimen was simple, safe, and accurate in predicting the daily maintenance warfarin dose in elderly hospitalized patients.

Evaluation of a warfarin initiation protocol for older people

A protocol for initiation of warfarin therapy, targeted specifically for older people and based on individual responses to initial warfarin doses, was evaluated in a case-control study. People within the protocol group: (i) received higher initial doses of warfarin, (ii) reached an international normalized ratio (INR) of 2 more quickly, (iii) spent more time with INR of 2-3 in the first week and (iv) were less likely to be over-anticoagulated. However, the proportion of people who reached an INR of 2 too quickly (in <4 days) was no greater. The protocol correctly predicted the maintenance dose range of warfarin in over 70% of cases.

Racial background is a determinant factor in the maintenance dosage of warfarin

Warfarin is a drug commonly used in the prevention of thromboembolic events. There have been reports suggesting that racial background may influence warfarin dose requirements. Malaysia is a multiracial country in which there are 3 major races, Malay, Chinese, and Indian. We examined 100 patients from our hospital on stable maintenance doses of warfarin, with international normalized ratio (INR) of 2.0 to 3.5. We found that the mean warfarin dose for Indian patients (n = 19) was 6.9 mg, for Chinese patients (n = 55) was 3.6 mg, and for Malay patients (n = 26) was 3.2 mg. The results showed that the Indian patients required a statistically significantly higher warfarin dose than did patients of the other 2 races (P < .0005). Age was also found to affect the daily warfarin maintenance dose.

Oral anticoagulants in the elderly

Over a 1-year period, 34,998 prothrombin time tests were performed on 2,379 patients aged 40-89 years with a recommended target International Normalized Ratio (INR) value of 2.5. At least one INR value of >/= 5 was found in 507/2,379 patients (21.3%). The elderly demonstrated higher maximum and lower minimum INR values, lower warfarin doses, and an increased number of tests performed. After adjustment for these factors, the risk of INR values >/= 5 increased with age by 15% every 10 years (95% CI 4-28%). We conclude that age is a risk factor for more unstable prothrombin time results.

The initial phase of oral anticoagulation with warfarin in outpatients with deep venous thrombosis

Patients with deep venous thrombosis (DVT) treated out of hospital usually start warfarin with the recommended 5 mg loading dose and have their International Normalized Ratio (INR) test performed every 2-3 days. Thus, achievement of the therapeutic range may be more difficult than for inpatients, possibly resulting in extended duration of low molecular weight heparin (LMWH) treatment. We retrospectively examined the charts of 55 DVT outpatients (mean age, 61.4 years; 30 males) to assess the actual duration of LMWH treatment and to identify predictors of a slow achievement of the INR range. Thirty patients (54.4%) reached the therapeutic INR range and stopped LMWH within 7 days, and 25 patients (45.6%) had to continue for an average of 10.5 days. The latter group was significantly younger than the former (57 and 65 years, respectively; P = 0.039). Patients younger than 60 years old had an odds ratio for an extended treatment of 4.92 (P = 0.0057). Algorithms with different loading doses of warfarin according to age should be proposed for outpatient treatment of DVT.

[Identification of factors responsible for oral over-anticoagulation in outpatients with heart disease]

BACKGROUND

Few studies have attempted to investigate the clinical course or identify factors responsible for excessive anticoagulation in patients with heart disease.

OBJECTIVES

To determine the incidence of excessive anticoagulation in outpatients with heart disease treated with acenocoumarol, analyze the factors related with over-anticoagulation, and identify bleeding complications.

PATIENTS AND METHOD

This 7-month prospective observational study included consecutive outpatients anticoagulated with acenocoumarol. They were seen in an anticoagulation unit. The high INR group of 55 over-anticoagulated patients had at least one test with INR > 5. The control group of 49 patients had INR results strictly within therapeutic range.

RESULTS

A total of 3,683 INR determinations were made in 512 patients. Seventy-seven tests had an INR > 5 (a 2% overall incidence of high-INR). In the group of 55 INR < 5 patients, 31% had more than one INR determination > 5 during follow-up. Multivariate analysis identified four variables as independent predictors of over-anticoagulation: artificial heart valve, poor treatment compliance, addition of potentially interactive new drugs, and illness in the last month. The high-INR group patients had more bleeding episodes (21.8 vs 4.08%; p = 0.008), one of which was major.

CONCLUSION

The incidence of excessive oral anticoagulation in our outpatient population was similar to that reported in other studies. Patients with INR > 5 had more total bleeding complications, mostly minor. It is recommended to proceed carefully with oral anticoagulant therapy in patients with an artificial heart valve, suspected poor treatment compliance, addition of potentially interactive new drugs, and illness in the last month.

Comparison of a daily fixed 2.5-mg warfarin dose with a 5-mg, international normalized ratio adjusted, warfarin dose initially following heart valve replacement

Patients starting oral anticoagulant therapy after heart valve replacement initially require a lower target international normalized ratio (INR) (2.0, range 1.5 to 2.6) because of a higher risk of bleeding until pericardial wires are removed. In a previous retrospective analysis, we observed a higher sensitivity to warfarin in these patients compared with nonsurgical patients. In a randomized clinical trial, we compared a fixed, lower dose of warfarin (2.5 mg) with the standard treatment consisting of a 5-mg loading dose, then adjusted to the target INR during the first 5 days of anticoagulation. INRs were measured daily, but the fixed dose was only modified on day 3 if the INR was <1.5 or >3.0. One hundred ninety-seven patients were considered eligible for the study. The 2 groups were well matched according to age, gender, body mass index, concomitant treatments, and type of valves implanted. The proportion of INRs >2.6 during the study period was 42.5% in the 5-mg group and 26.2% in the 2.5-mg group (p <0.05), and the proportion of INRs >3.0 on day 3 was 23.9% and 9.5% (p <0.05), respectively. In the 2.5-mg group, 35.7% of patients had an INR <1.5 on day 3 and had the dose increased (vs 3.5%, p <0.001); however, in the 5-mg group, 95.6% had the initial dose reduced, 49.6% had the dose withheld for at least 1 day, and the mean dose during the 5 days of study was 3.08 mg. Average time to achieve therapeutic range was higher in the 2.5-mg group (2.72 vs 1.98 days, p <0.0001), but the approach to the targeted INR was more regular, and the gap between target and mean INR on day 5 was smaller. There were no bleeding or thromboembolic complications in either group. Thus, a lower loading dose of warfarin in patients after heart valve replacement reduces excessive anticoagulation and offers a more regular achievement of the therapeutic target by reducing the number of dose adjustments. Daily monitoring of the INR is still recommended.

Evaluation of warfarin initiation regimens in elderly inpatients

STUDY OBJECTIVE

To compare initial warfarin doses of 5 mg or below and doses above 5 mg in hospitalized elderly.

DESIGN

Retrospective review of charts identified from computerized pharmacy records.

SETTING

County teaching hospital.

PATIENTS

Inpatients aged 65 years or older receiving at least three warfarin doses.

INTERVENTION

We measured the time to first international normalized ratio (INR) of 2.0 or greater, bleeding complications, number of warfarin doses held, and vitamin K use.

MEASUREMENTS AND MAIN RESULTS

The average initial low dose (33 patients) was 4.8 +/- 0.8 mg and the average initial high dose (40 patients) was 9.0 +/-1.2 mg. The mean time to first INR of 2.0 or greater was similar, 3.4 and 3.0 days, respectively (p=0.38). The low-dose group had fewer bleeds (7 vs 13, p=0.28) and doses held (11 vs 18 patients, p=0.27, 30 vs 50 doses). Four patients in each group received vitamin K (p=0.8). Forty-four percent of patients with an INR of 4 or above and 48% of patients who had a dose held were on a long-term drug or had a new drug added that could cause a major drug interaction with warfarin.

CONCLUSION

In this pilot study, hospitalized elderly who received a low versus high initial dose of warfarin achieved therapeutic INRs in a similar time and had lower but not significantly different safety outcomes.

Use of oral anticoagulants in older patients

Recently published American and British guidelines have comprehensively reviewed the indications for long term anticoagulation. The best evidence currently available supports the use of long term oral anticoagulants in patients with nonvalvular atrial fibrillation (NVAF), venous thromboembolic disease, ischaemic heart disease, mural thrombi, and mechanical heart valves. Selected patients with valvular heart disease, cerebral vascular disease, and peripheral arterial disease may also benefit from the use of these drugs. When no specific contraindications are present, elderly patients with either paroxysmal or persistent NVAF should be considered candidates for treatment with anticoagulants. Pooled analyses of the results from 9 randomised trials demonstrate that warfarin significantly reduces the risk of ischaemic stroke in patients with NVAF, particularly those in a 'high risk' category defined by the presence of additional clinical or echocardiographic risk factors. Long term anticoagulation does not appear to be justified in patients with NVAF considered to be at 'low risk' for stroke. Because the prevalence of NVAF and most other cardiovascular conditions increases with advancing age, many elderly patients will be candidates for thromboprophylaxis. The potential benefit of long term anticoagulation must be carefully weighed against the risk of serious haemorrhage in such patients. Bleeding complications with anticoagulant drugs appear to occur more frequently in older patients than in younger individuals. Advanced age (>75 years), intensity of anticoagulation [International Normalised Ratio (INR) >4.0], history of cerebral vascular disease (recent or remote), and concomitant use of drugs that interfere with haemostasis [aspirin (acetylsalicylic acid) or nonsteroidal anti-inflammatory drugs] are among the most important variables in determining an individual's risk for major bleeding with anticoagulants. Older patients often display increased sensitivity to the effects of warfarin, both in the early induction phase and during the long term maintenance phase of therapy. Conditions such as congestive heart failure, malignancy, malnutrition, diarrhoea and unsuspected vitamin K deficiency, enhance the prothrombin time response. The decision to interrupt anticoagulant therapy before elective surgery in elderly patients should evaluate the thrombotic risk of such a manoeuvre versus the risk of bleeding if anticoagulants are continued. In non-surgical patients, excessively elevated INRs without associated haemorrhage can usually be managed by simply witholding one or several doses of warfarin. If more rapid reversal is needed, small doses of phytomenadione (vitamin K1) can be administered safely without overcorrection or the development of vitamin K-induced warfarin resistance.

Exaggerated initial response to warfarin following heart valve replacement

The response to initiation of oral anticoagulants at a usual dose of 5 mg of warfarin has been retrospectively evaluated in patients following heart valve replacement (HVR). Patients starting oral anticoagulants after HVR have a lower target International Normalized Ratio (INR) (1.5 to 2.6) until the pacing wires are removed after operation. The mean daily doses and INR responses after HVR and nonsurgical patients were retrospectively compared during the first 5 days of warfarin treatment. In a subset from both groups, the mean dose of warfarin was correlated with age, body weight, and albumin levels. Eighty-four HVR and 32 nonsurgical patients were studied. The mean daily warfarin dosage was 3.29 +/- 1.29 mg after HVR and 4.96 +/- 1.76 mg in controls (p <0.001), and the mean INRs 2.08 +/- 0.60 and 1.60 +/- 0.54, respectively (p <0.001). Of the HVR patients and controls, 48.8% and 21.8%, respectively, exceeded the upper level of the targeted range (p = 0.014), 86.9% and 40.6% had the dose reduced after the first 5 mg (p <0.001), and 54.7% and 28.1%, respectively, had warfarin withheld for at least 1 day (p = 0.015). Thirty-nine patients were included in the subset analysis. Patients with serum albumin levels <35 g/L required significantly less warfarin (3.84 mg/day) than patients with levels > or =35 g/L (5.37 mg/day; p <0.05). Thus, patients starting oral anticoagulation after HVR are significantly more sensitive to warfarin than nonsurgical patients. Patients with serum albumin levels below the normal values require less warfarin than patients with normal values during the initial phase of treatment.

Warfarin responses in total joint and hip fracture patients

Warfarin is considered as a narrow therapeutic drug-an agent for which small changes in dosage can lead to significant changes in response. The precision of warfarin treatment is especially relevant in an acute-care setting. In this study, we examined the effect of various risk factors on warfarin response in the early postoperative period after total joint arthroplasty and hip fracture fixation. A total of 260 patients placed on warfarin for thrombosis prophylaxis were retrospectively studied. Risk factors for warfarin sensitivity include age 80 years or older and hip fracture fixation. Patients aged 80 years or older who had hip fracture fixation were 4.7 times more likely to experience an international normalized ratio (INR) at or greater than 4.0 than other patients (therapeutic target range of INR, 1.8-2.2). The largest subtherapeutic risk group in this study were men weighing 180 lb or more. They were 5.7 times less likely to achieve an INR of 1.6 than the other patients. Factors such as body weight, age, and gender should be considered when ordering warfarin therapy. Current hospital warfarin sliding scales should be reviewed for their efficacy to ensure that the target outcome is achieved.

Audit of the frequency and clinical response to excessive oral anticoagulation in an out-patient population

A retrospective review of over-anticoagulated patients with critical international normalized ratios (INRs) was undertaken in a large outpatient laboratory. In the six-month study period, 85 prothrombin times (PTs) were identified with an INR of > or = 6.0, an overall incidence of elevated PTs of 0.2% or two per 1,000 INR tests. Complete follow-up data was available on 65 patients. When compared to an age- and gender-matched control group without INR > or = 6.0, high-INR patients were significantly more likely to manifest the presence of alcoholism or liver disease, to have been anticoagulated for less than six months, to have experienced more frequent warfarin dosage changes, and to have had the addition of a medication known to interact with warfarin. In the high-INR group, a likely cause for the specific critical INR was identified in 44 patients (68%). Drug interactions followed by compliance problems were the most common factors identified. The 13 patients (20%) who received vitamin K therapy experienced no difference in the clinical outcome compared with those managed conservatively. Conservative management of critically high INR values appeared to be as efficacious as intervention with vitamin K therapy.

A warfarin induction regimen for out-patient anticoagulation in patients with atrial fibrillation

Currently available protocols for induction of warfarin anticoagulation employ initial doses of 10 mg and are best suited to in-patient use. However, with the increasing number of elderly patients with atrial fibrillation requiring anticoagulation, there is a need for a less intense regimen which could be used for out-patients. We have established such a regimen and report on its prospective evaluation in 3 7 patients referred for out-patient initiation of warfarin, and a non-randomized comparison with 37 in-patients, with similar diagnoses, commenced on a traditional warfarin protocol. After exclusion of five patients on amiodarone, all of whom experienced supratherapeutic International Normalized Ratio (INR) results, the new out-patient regimen, employing an initial 5 mg dose, resulted in a lower maximum INR during the first 21 d therapy (median 2.9 v 4.0; P = 0.0001) and fewer INRs >4.5 (2/36 v 9/33) compared to the traditional 10 mg regimen. Time to reach stable anticoagulation was similar with each regimen; however, the 5 mg regimen gave a more accurate prediction of maintenance dose (correlation coefficient for predicted versus actual maintenance dose, r = 0.985). In comparison to a traditional 10 mg protocol, the proposed 5 mg warfarin induction regimen proved both safer and more reliable for initiation of prophylactic anticoagulation in patients with atrial fibrillation.

Current recommendations for warfarin therapy. Use and monitoring

With the aging population, the use of warfarin will continue to increase. The introduction of new thromboplastins with International Sensitivity Indices (ISI) of 1.0 to 1.5 has improved the efficacy of monitoring warfarin therapy with the prothrombin time (PT). Increasingly, outpatient oral anticoagulant clinics and home testing are the sites for PT monitoring.

Management of oral anticoagulant-induced intracranial haemorrhage

Intracranial haemorrhage is an infrequent but often fatal complication of oral anticoagulant therapy which will become more common as anticoagulant use increases. The risk of anticoagulant-induced intracranial haemorrhage may be reduced by judicious prescribing, identification of patients at high risk of bleeding, and close monitoring by experienced staff. The presenting features of intracranial haemorrhage are often vague and physicians should be aware of the need for urgent investigation of all anticoagulated patients with neurological symptoms. Current guidelines for immediate reversal of anticoagulation recommend administration of vitamin K1 and factor replacement with either factor concentrates or fresh frozen plasma. In this review we discuss recent evidence suggesting prothrombin complex concentrates lead to faster, and more complete, correction of coagulation and, in the context of intracranial bleeding, may be associated with improved neurological status. Evidence for the risks of short-term cessation of anticoagulants, in the immediate period following an intracranial haemorrhage, and their subsequent reintroduction is also discussed.

Outpatient anticoagulation issues for the primary care physician

Increasingly, primary care providers are caring for patients who require anticoagulation. In this article the indications for, complications of, and methods of dosing and monitoring warfarin in the outpatient setting are reviewed. Heparin use among ambulatory patients also is discussed.