Age-dependent differences in the anticoagulant effect of phenprocoumon in patients after heart valve surgery

Age-related pharmacodynamics in a bumblebee-microsporidian system mirror similar patterns in vertebrates

Immune systems provide a key defence against diseases. However, they are not a panacea and so both vertebrates and invertebrates co-opt naturally occurring bioactive compounds to treat themselves against parasites and pathogens. In vertebrates, this co-option is complex, with pharmacodynamics leading to differential effects of treatment at different life stages, which may reflect age-linked differences in the immune system. However, our understanding of pharmacodynamics in invertebrates is almost non-existent. Critically, this knowledge may elucidate broad parallels across animals in regard to the requirement for the co-option of bioactive compounds to ameliorate disease. Here, we used biochanin A, an isoflavone found in the pollen of red clover (Trifolium pratense), to therapeutically treat Nosema bombi (Microsporidia) infection in bumblebee (Bombus terrestris) larvae and adults, and thus examine age-linked pharmacodynamics in an invertebrate. Therapeutic treatment of larvae with biochanin A did not reduce the infection intensity of N. bombi in adults. In contrast, therapeutic treatment of adults did reduce the infection intensity of N. bombi This transition in parasite resistance to bioactive compounds mirrors the age-linked pharmacodynamics of vertebrates. Understanding how different life-history stages respond to therapeutic compounds will provide novel insights into the evolution of foraging and self-medication behaviour in natural systems more broadly.

Risk of traumatic intracranial haemorrhage is increased in older people exposed to oral anticoagulation with phenprocoumon

BACKGROUND

Hospital admissions resulting from traumatic intracranial haemorrhages (TIH) in older people are increasing. There are concerns regarding an increased risk of a TIH in people taking oral anticoagulants (OAC) like phenprocoumon.

AIMS

The aim of this study was to estimate the incremental risk of a TIH associated with OAC in older people. Furthermore, this study explored differences in risk according to functional status.

METHODS

The study took data from a large German health insurance provider and combined hospital diagnoses with data regarding drug dispensing to estimate rates of a TIH in people with and without exposure to phenprocoumon. Analyses were stratified by sex and by severe functional impairment as disclosed by the long-term care insurance provider.

RESULTS

Overall, exposure to OAC resulted in 2.7 times higher rates of TIH. People with severe functional impairment had a higher baseline risk of TIH than people without severe functional impairment. However, the incremental risk in those exposed to OAC was similar among people with and without severe functional impairment (standardised incidence rate difference 15.73 (95% CI 7.84; 23.61) and 12.10 (95% CI 9.63; 14.57) per 10,000 person-years, respectively).

CONCLUSIONS

OAC increases the risk of TIH considerably. The incremental risk of TIH in those exposed to OAC is comparable between people with and without severe functional impairment. The presence of severe functional impairment per se should not exclude such patients from the potential benefits of OAC. For now, the prescription should be personalized based on individual fall risk factors and risk-taking behaviour.

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.

Changes in Pharmacokinetics and Pharmacodynamics in the Elderly Patient

The use of pharmacologic agents in elderly patients is one of the most difficult aspects of patient care. An understanding of the common physiologic changes expected with aging is helpful to anticipate changes expected in pharmacokinetic parameters. Distribution, metabolism, and excretion are significantly altered for many drugs. In addition, pharmacodynamic variations in elderly patients may increase or decrease sensitivity to a medication independent of pharmacokinetic changes. These alterations are particularly noteworthy with cardiovascular and central nervous system agents. Current controversies regarding the application of estimation of renal function to drug dosing and use of the Beers criteria of medications potentially inappropriate in the elderly are discussed.

Cells and extracellular matrix interplay in cardiac valve disease: because age matters

Cardiovascular aging is a physiological process affecting all components of the heart. Despite the interest and experimental effort lavished on aging of cardiac cells, increasing evidence is pointing at the pivotal role of extracellular matrix (ECM) in cardiac aging. Structural and molecular changes in ECM composition during aging are at the root of significant functional modifications at the level of cardiac valve apparatus. Indeed, calcification or myxomatous degeneration of cardiac valves and their functional impairment can all be explained in light of age-related ECM alterations and the reciprocal interplay between altered ECM and cellular elements populating the leaflet, namely valvular interstitial cells and valvular endothelial cells, is additionally affecting valve function with striking reflexes on the clinical scenario. The initial experimental findings on this argument are underlining the need for a more comprehensive understanding on the biological mechanisms underlying ECM aging and remodeling as potentially constituting a pharmacological therapeutic target or a basis to improve existing prosthetic devices and treatment options. Given the lack of systematic knowledge on this topic, this review will focus on the ECM changes that occur during aging and on their clinical translational relevance and implications in the bedside scenario.

Age-related changes in aortic valve hemostatic protein regulation

OBJECTIVE

Although valvular endothelial cells have unique responses compared with vascular endothelial cells, valvular regulation of hemostasis is not well-understood. Heart valves remodel throughout a person's lifetime, resulting in changes in extracellular matrix composition and tissue mechanical properties that may affect valvular endothelial cell hemostatic function. This work assessed valvular endothelial cell regulation of hemostasis in situ and in vitro as a function of specimen age.

APPROACH AND RESULTS

Porcine aortic valves were assigned to 1 of 3 age groups: Young (YNG) (6 weeks); Adult (ADT) (6 months); or Elderly (OLD) (2 years). Histological examination of valves showed that secreted thrombotic/antithrombotic proteins localize at the valve endothelium and tissue interior. Gene expression and immunostains for von Willebrand factor (VWF), tissue factor pathway inhibitor, and tissue plasminogen activator in YNG porcine aortic valve endothelial cells were higher than they were for OLD, whereas plasminogen activator inhibitor 1 levels in OLD were higher than those for YNG and ADT. Histamine-stimulated YNG porcine aortic valve endothelial cells released higher concentrations of VWF proteins than OLD, and the fractions of VWF-140 fragments was not different between age groups. A calcific aortic valve disease in vitro model using valvular interstitial cells confirmed that VWF in culture significantly increased valvular interstitial cell nodule formation and calcification.

CONCLUSIONS

Hemostatic protein regulation in aortic valve tissues and in valvular endothelial cells changes with age. The presence of VWF and other potential hemostatic proteins increase valvular interstitial cell calcification in vitro. Therefore, the increased capacity of elderly valves to sequester the hemostatic proteins, together with age-associated loss of extracellular matrix organization, warrants investigation into potential role of these proteins in the formation of calcific nodules.

VKORC1 and CYP2C9 Genotype Variations in Relation to Warfarin Dosing in Korean Stroke Patients

Background and Purpose

Variant alleles of CYP2C9 and VKORC1 account for differences in anticoagulation response. We sought to establish a warfarin dosing formula for individualized target International Normalization Ratio of Prothrombin Times (INRs) using data from single nucleotide polymorphisms (SNPs) in VKORC1 and CYP2C9 in Korean patients.

Methods

Ischemic stroke patients displaying stable target INR for at least 3 months before enrollment were analyzed. Warfarin and vitamin K levels were measured to adjust for confounders. Phenotypes were defined using the 'warfarin response index' (WRI) defined as INR divided by the daily maintenance warfarin dose. We tested SNPs in CYP2C9 (3 sites: 430C>T (rs1799853), 1075A>C (rs1057910), 1076T>C) and VKORC1 (14 sites: 381C>T, 861C>A (rs17880887), 2653G>C, 3673A>G, 5496G>T, 5808T>G (r17882154), 6009C>T, 6484T>C (rs9934438), 6853C>T (rs17886369), 7566T>C, 8767G>C, 8814T>C, 9041G>A (rs17880624), and 9071G>T) using a standard sequencing method. Multivariate linear regression analysis was applied to establish the formula for warfarin dosage.

Results

All 204 patients had excellent drug compliance. The mean INR was 2.22 (+0.56) and mean daily maintenance dose of warfarin was 3.92 mg (+1.54). Patients with low WRI were younger (P<0.001) with high body mass index (P=0.003), high prevalence of wild-type CYP2C9 polymorphism (1075A>C, P<0.001), and six heterozygote SNPs in VRORC1 (P<0.001), which were tightly interlinked (381T>C, 3673G>A, 6484T>C, 6853C>G. 7566C>T, 9041G>A) (r²=1). Based on these data, a warfarin dosing formula was established.

Conclusions

WRI is influenced by age, body mass index and SNPs in VKORC1 and CYP2C9 in Korean stroke patients. The obtained warfarin dosing formula may be clinically applicable.

Incidence, clinical impact and risk of bleeding during oral anticoagulation therapy

Bleeding is the most important complication of oral anticoagulation (OAC) with vitamin K-antagonists. Whilst bleeding is unavoidably related to OAC, it may have a great impact on the prognosis of treated subjects by leading to discontinuation of treatment, permanent disability or death. The yearly incidence of bleeding during OAC is 2%-5% for major bleeding, 0.5%-1% for fatal bleeding, and 0.2%-0.4% for intracranial bleeding. While OAC interruption and/or antagonism, as well as administration of coagulation factors, represent the necessary measures for the management of bleeding, proper stratification of the individual risk of bleeding prior to start OAC is of paramount importance. Several factors, including advanced age, female gender, poor control and higher intensity of OAC, associated diseases and medications, as well as genetic factors, have been proven to be associated with an increased risk of bleeding. Most of these factors have been included in the development of bleeding prediction scores, which should now be used by clinicians when prescribing and monitoring OAC. Owing to the many limitations of OAC, including a narrow therapeutic window, cumbersome management, and wide inter- and intra-individual variability, novel oral anticoagulants, such as factor Xa inhibitors and direct thrombin inhibitors, have been recently developed. These agents can be given in fixed doses, have little interaction with foods and drugs, and do not require regular monitoring of anticoagulation. While the novel oral anticoagulants show promise for effective thromboprophylaxis in atrial fibrillation and venous thromboembolism, definitive data on their safety and efficacy are awaited.

Risk factors for bleeding during anticoagulation of atrial fibrillation in older and younger patients in clinical practice

BACKGROUND

The prevalence of atrial fibrillation increases with age, affecting approximately 5% of people aged >65 years and almost 10% of people aged >80 years.

OBJECTIVE

The goal of this study was to identify risk factors for bleeding during warfarin treatment of nonvalvular atrial fibrillation (NNVAF) in older patients (those aged >or=75 years) compared with younger patients (those aged <75 years) in clinical practice.

METHODS

All patients with NVAF newly started on warfarin at an anticoagulation clinic in a large university hospital were included in this prospective observational study. Patient details were recorded at their first visit; details of any bleeding events were recorded via telephone interview every 4 to 6 weeks for a minimum of 10 months. Patients were divided into 2 groups (ie, those >or=75 years old and those <75 years old). Logistic regression analysis was used to identify risk factors for bleeding.

RESULTS

A total of 402 patients were included in the study. Group I comprised 203 patients <75 years old (mean [SD] age, 64.33 [8.33] years) and group II comprised 199 patients >or=75 years old (mean [SD] age, 80.44 [3.99] years). Follow-up ranged from 1 to 31 months (mean [SD], 19 [8.11] months). For major bleeding, number of medications was a significant risk factor in older patients (odds ratio [OR], 3.0; 95% CI, 1.2-7.8 [P = 0.02 ]) and range of the international normalized ratio (INR) was a significant risk factor in both groups. For every unit increase in the range of INR, the odds of major bleeding increased by 0.6 (OR, 1.6; 95% CI, 1.2-2.4 [P = 0.03 ]) in younger patients and by 0.4 (OR, 1.4; 95% CI, 1.07-1.99 [P = 0.04 ])in older patients. For minor bleeding, history of hypertension was the only significant risk factor in older patients (OR, 3.3; 95% CI, 1.3-8.1 [P = 0.01 ]), while history of ischemic heart disease was the only risk factor in younger patients (OR, 1.9; 95% CI, 1.1-5.4 [P = 0.04 ]).

CONCLUSIONS

Bleeding pattern was similar in both age groups regarding severity, onset, anatomic site of bleeding, and INR values during the bleeding event. Risk factors for episodes of major bleeding, which are more of a clinical concern, are potentially modifiable. They include quality of anticoagulation control in both groups and number of medications in the older age group.

Pharmacodynamics in older adults: a review

BACKGROUND

Older individuals experience physiologic changes in organ function related to aging or to specific disease processes. These changes can affect drug pharmacodynamics in older adults.

OBJECTIVE

The goal of this article was to review age-related changes in pharmacodynamics and their clinical relevance.

METHODS

PubMed and International Pharmaceutical Abstracts were searched (January 1980-June 2006) for the following combination of terms: pharmacodynamic and elderly, geriatric or aged. References cited in other reviews were also evaluated. The current review focused on age-related pharmacodynamic changes in agents affecting the central nervous system (CNS), cardiovascular, and endocrine functions.

RESULTS

Older adults frequently demonstrate an exaggerated response to CNS-active drugs. This is in part due to an underlying age-related decline in CNS function and in part due to increased pharmacodynamic sensitivity for some benzodiazepines, anesthetics, and opioids. The most important pharmacodynamic differences with age for cardiovascular agents are the decrease in effect for beta-adrenergic agents. This decline in response in vascular, cardiac, and pulmonary tissue may be due to a decrease in Gs protein interactions. Most studies indicate there is no decrease in cx-receptor sensitivity with age. Angiotensin-converting enzyme inhibitors do not show age-related differences in elderly patients. With the dihydropyridine calcium channel blockers, there was a slight increase in effect for older adults, but this was only for treatment-naive patients and was transient. Nondihydropyridines did not show an age- associated change in pharmacodynamic effect; however, in the elderly, there appeared to be a decrease in the PR interval prolongation normally seen with these agents. Studies of diuretics indicated that the changes in diuretic and natriuretic effects seen in the elderly were associated with pharmacokinetic changes and were not pharmacodynamic in nature. There was a lack of consistent evidence regarding whether sulfonylureas show age-related changes in pharmacodynamic effect.

CONCLUSIONS

There is a general trend of greater pharmacodynamic sensitivity in the elderly; however, this is not universal, and these age-related changes must be investigated agent-by-agent until further research yields greater understanding of the molecular mechanisms underlying the aging process.

Obesity is associated with a slower response to initial phenprocoumon therapy whereas CYP2C9 genotypes are not

BACKGROUND

Initiation of phenprocoumon therapy is associated with a variable individual response. The CYP2C9 genotype has been shown to influence the response to warfarin therapy, but such an effect on phenprocoumon therapy remains uncertain.

METHOD

Two hundred sixty hospital patients started on phenprocoumon were recruited for this study. Body mass index (BMI), waist and hip circumference, dietary habits, comorbidity, and comedication were initially assessed. A 5' exonuclease assay (TaqManR) was used to analyze the presence of five polymorphisms of the CYP2C9 gene in each of the study patients. Study endpoints included the time necessary to achieve the international normalized ratio (INR) target (INR >2) and the total drug amount required to attain target INR. For 250 of 260 patients, the subsequent required daily maintenance dose of phenprocoumon was also recorded.

RESULTS

Both the necessary time and total dose required to attain target INR correlated significantly with BMI. The leaner the patient, the shorter the required time interval [BMI <22 (n=31), 5.48+/-2.49 days; BMI 22-25 (n=70), 6.09+/-2.40; BMI 25-30 (n=113), 6.76+/-3.61; BMI >30 (n=46), 8.50+/-5.75; p=0.001] and the lower the required dosage until the therapeutic range was achieved [BMI <22 (n=31), 23.8+/-12.1 mg; BMI 22-25 (n=70), 25.9+/-11.4 mg; BMI 25-30 (n=113), 29.6+/-25.2; BMI >30 (n=46), 35.8+/-19.7; p=0.027]. Overweight and waist circumference as a surrogate marker for abdominal fat were also associated significantly with these two parameters. Moreover, obesity was associated with a lower body-weight-adjusted maintenance dosage. All CYP2C9 genotypes that were tested failed to reveal an association with individual response variability.

CONCLUSION

Patient obesity appears to directly correspond to the amount of phenprocoumon required during initiation of therapy. The CYP2C9 genotype was not shown to influence the necessary therapeutic dosage.

Comparative Pharmacokinetics of Vitamin K Antagonists

Vitamin K antagonists belong to the group of most frequently used drugs worldwide. They are used for long-term anticoagulation therapy, and exhibit their anticoagulant effect by inhibition of vitamin K epoxide reductase. Each drug exists in two different enantiomeric forms and is administered orally as a racemate. The use of vitamin K antagonists is complicated by a narrow therapeutic index and an unpredictable dose-response relationship, giving rise to frequent bleeding complications or insufficient anticoagulation. These large dose response variations are markedly influenced by pharmacokinetic aspects that are determined by genetic, environmental and possibly other yet unknown factors. Previous knowledge in this regard principally referred to warfarin. Cytochrome P450 (CYP) 2C9 has clearly been established as the predominant catalyst responsible for the metabolism of its more potent S-enantiomer. More recently, CYP2C9 has also been reported to catalyse the hydroxylation of phenprocoumon and acenocoumarol. However, the relative importance of CYP2C9 for the clearance of each anticoagulant substantially differs. Overall, the CYP2C9 isoenzyme appears to be most important for the clearance of warfarin, followed by acenocoumarol and, lastly, phenprocoumon. The less important role of CYP2C9 for the clearance of phenprocoumon is due to the involvement of CYP3A4 as an additional catalyst of phenprocoumon hydroxylation and significant excretion of unchanged drug in bile and urine, while the elimination of warfarin and acenocoumarol is almost completely by metabolism. Consequently, the effects of CYP2C9 polymorphisms on the pharmacokinetics and anticoagulant response are also least pronounced in the case of phenprocoumon; this drug seems preferable for therapeutic anticoagulation in poor metabolisers of CYP2C9. In addition to these vitamin K antagonists, oral thrombin inhibitors are currently under clinical development for the prevention and treatment of thromboembolism. Of these, ximelagatran has recently gained marketing authorisation in Europe. These novel drugs all feature some major advantages over traditional anticoagulants, including a wide therapeutic interval, the lack of anticoagulant effect monitoring and a low drug-drug interaction potential. However, they are also characterised by some pitfalls. Amendments of traditional anticoagulant therapy, including self-monitoring of international normalised ratio values or prospective genotyping for individual dose-tailoring may contribute to the continuous use of warfarin, phenprocoumon and acenocoumarol in the future.

Drug therapy in the elderly

Drug dosage in the elderly requires an understanding of the age-dependent changes in drug disposition and sensitivity. The most important pharmacokinetic alteration is a decline in renal function, the elderly should therefore be treated as renally insufficient patients. Metabolic clearance is primarily reduced with drugs that display high hepatic extraction, whereas the metabolism of drugs with low hepatic extraction usually is not diminished. The reduction of metabolic clearance is especially pronounced in malnourished or frail patients. The water content of the aging body decreases, the fat content rises. Hence the distribution volume of hydrophilic drugs may be reduced in the elderly, resulting in increased plasma concentrations. In contrast, the distribution volume of liphophilic drugs is increased, their plasma concentrations may decrease. Intestinal absorption of most drugs is not altered in the elderly. Aside of these pharmacokinetic changes, one of the characteristics of old age is a progressive decline in counterregulatory (homeostatic) mechanisms. Therefore, drug effects are attenuated less, the responses are usually stronger than in younger subjects, the rate and intensity of adverse effects are higher. Examples of drug actions augmented is this manner are postural hypotension with agents that lower blood pressure, dehydration and electrolyte disturbances in response to diuretics, bleeding complications with oral anticoagulants, hypoglycemia with antidiabetics, and gastrointestinal irritation with non-steroidal anti-inflammatory drugs. The brain is an especially sensitive drug target in old age. Psychotropic drugs, anticonvulsants, and centrally acting antihypertensives may impede intellectual function and motor coordination. Hence drugs should be used restrictively in geriatric patients.

A Six-Year Experience with the Omnicarbon Valve in North American Patients

AIM

We studied the results of an all-carbon monoleaflet valve prosthesis (the Omnicarbon) in a North American population.

METHODS

Patients were recalled to our valve clinic for complete evaluation, including echocardiography, laboratory tests, and physician examination. This experience includes 108 Omnicarbon valve implants. We report the results of single aortic (AVR) or mitral (MVR) valve replacement.

RESULTS

Patients' ages ranged from 40 to 83 (mean: 63 +/- 9 years), and most were male (60%, 59/98). Preoperatively, 71% were NYHA Classes III/IV, while most patients are now Classes I/II (86%). AVR predominated (63%, 62/98), and many patients (44%, 43/98) underwent cardiac procedures either previously or concomitant with valve replacement. Hospital mortality was 6.1% (6/98). Predicted hospital mortality using the Parsonnet additive risk model averaged 12.1%. Currently, four patients cannot be located (96% accountability). Overall, hematology indicated low hemolysis-lactate dehydrogenase: 691 +/- 184 IU/L (112%+/- 30% upper normal), reticulocytes: 1.8%+/- 0.7%, and red blood cells (10(6)/mm(3)): 4.41 +/- 0.50 (males)/4.16 +/- 0.50 (females). International normalized ratio averaged 2.67 +/- 0.72. Doppler echocardiography values were acceptable and comparable to other mechanical valves. Five-year survival (hospital death included) is 86%+/- 4%. At 5 years, freedom from any thromboembolic event is 99%+/- 1%, and freedom from bleeding is 97%+/- 2%. Endocarditis and nonstructural dysfuction also occurred at low rates (99%+/- 1% freedom at five years), and no structural failure or hemolytic anemia was observed during the 343 patient-years (mean: 3.7 +/- 1.6 years).

CONCLUSIONS

Good hematology and hemodynamics, along with remarkably low complication rates, demonstrate that the Omnicarbon valve meets contemporary performance expectations.

When drug therapy gets old: pharmacokinetics and pharmacodynamics in the elderly

The age-related changes in the functions and composition of the human body require adjustments of drug selection and dosage for old individuals. Drug excretion via the kidneys declines with age, the elderly should therefore be treated as renally insufficient patients. The metabolic clearance is primarily reduced with drugs that display high hepatic extraction ('blood flow-limited metabolism'), whereas the metabolism of drugs with low hepatic extraction ('capacity-limited metabolism') usually is not diminished. Reduction of metabolic drug elimination is more pronounced in malnourished or frail subjects. The water content of the aging body decreases, the fat content rises, hence the distribution volume of hydrophilic compounds is reduced in the elderly, whereas that of lipophilic drugs is increased. Intestinal absorption of most drugs is not altered in the elderly. Aside of these pharmacokinetic changes, one of the characteristics of old age is a progressive decline in counterregulatory (homeostatic) mechanisms. Therefore drug effects are mitigated less, the reactions are usually stronger than in younger subjects, the rate and intensity of adverse effects are higher. Examples of drug effects augmented is this manner are postural hypotension with agents that lower blood pressure, dehydration, hypovolemia, and electrolyte disturbances in response to diuretics, bleeding complications with oral anticoagulants, hypoglycemia with antidiabetics, and gastrointestinal irritation with non-steroidal anti-inflammatory drugs. The brain is an especially sensitive drug target in old age. Psychotropic drugs but also anticonvulsants and centrally acting antihypertensives may impede intellectual functions and motor coordination. The antimuscarinic effects of some antidepressants and neuroleptic drugs may be responsible for agitation, confusion, and delirium in elderly. Hence drugs should be used very restrictively in geriatric patients. If drug therapy is absolutely necessary, the dosage should be titrated to a clearly defined clinical or biochemical therapeutic goal starting from a low initial 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.

Factors affecting warfarin therapy following cardiac valve surgery

OBJECTIVE

To determine the factors that affect the initial response to warfarin therapy in Korean patients after cardiac valve surgery.

METHODS

A retrospective analysis of 127 patients who had undergone cardiac valve surgery at Seoul National University Hospital was performed. On the first day, most patients received warfarin 5 mg, while some received an individualized warfarin dose according to their physician's decision. Doses to be given on the following days were determined based on daily international normalized ratio (INR) and the previous doses. To measure warfarin sensitivity, the warfarin dose index (WDI), defined as the INR divided by the mean warfarin dose administered during the preceding 3 days, was introduced. The effects of age, gender, weight, serum albumin concentration, baseline INR, cardiopulmonary bypass time, and concurrent administration of amiodarone were evaluated.

RESULTS

The patients' weight, initial serum albumin concentration, and baseline INR value influenced their initial response to warfarin. The initial WDI correlated negatively with the initial serum albumin concentration (p < 0.001) and body weight (p < 0.05) and positively with the baseline INR (p < 0.01). The initial WDI of the patients taking amiodarone was significantly higher (mean +/- SD 0.74 +/- 0.34) than that of patients without amiodarone (0.46 +/- 0.22) (p < 0.001). Maintenance doses correlated negatively with the initial warfarin response (p < 0.001) and positively with body weight (p = 0.053).

CONCLUSIONS

The factors associated with an increased initial warfarin response in patients after cardiac valve surgery were high baseline INR, low postoperative serum albumin concentration, and concurrent administration of amiodarone. Thus, patients with any of these factors should receive a smaller initial warfarin dose. Also, to predict the warfarin maintenance dose from the initial response, the effect of transient changes in the sensitivity to warfarin during the initial period should be considered.

[Current recommendations for prevention of thromboembolic events in patients with heart valve prostheses]

Within the last few years, marked progress has been made in the prevention of thromboembolic events in patients with mechanical heart valves. Thus, therapy has become more effective and is associated with less risk. This includes a number of developments like the introduction of the internationalized, normalized ratio (INR) for determination of the intensity of anticoagulation, the concept of a risk factor-adjusted, prosthesis specific, individualized indication for and intensity of anticoagulation and the possibility for self-determination of anticoagulation intensity by the patient. Prospective, randomized studies on the effect of different intensities of anticoagulation allowed definitions of individualized anticoagulation target levels and were the basis for guidelines on clinical management of anticoagulation. In spite of this progress, thromboembolic complications and anticoagulation associated bleedings are still the most frequent complications after valve replacement. The guidelines published by the professional societies on anticoagulation should be followed more closely in daily clinical practice. The management of oral anticoagulant treatment can be improved by following the concept of a risk factor-adjusted indication for and intensity of oral anticoagulant treatment as well as the use of the INR for monitoring the intensity of anticoagulation. Intensive education of the patient, implementation of self-testing by suitable patients and increasing the frequency of testing can further contribute to improvement.

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.