Dose response characterization of the association of serum digoxin concentration with mortality outcomes in the Digitalis Investigation Group trial.

AIMS: Many patients with heart failure and reduced EF remain at high risk for hospitalization despite evidence-based therapy. Digoxin may decrease hospitalization; however, uncertainty persists concerning its proper administration and effect on mortality. This study investigated whether using dose response concepts to re-evaluate the relationship between serum digoxin concentration and key mortality outcomes in patients with reduced EF in the Digitalis Investigation Group trial would help clarify efficacy and safety. METHODS AND RESULTS: Multivariable Cox proportional hazards modelling and propensity score adjustment assessed the relationship between serum digoxin concentration (≥0.5 ng/mL) as a continuous variable and mortality outcomes. In patients treated with digoxin, a significant linear association was found between serum concentration and all-cause mortality [adjusted hazard ratio (HR) 1.25, 95% confidence interval (CI) 1.14-1.38, P < 0.001 per 0.5 ng/mL increase in serum concentration]. Based on this relationship, a bidirectional association was found between digoxin therapy and all-cause mortality when compared with placebo. The lowest serum concentrations (0.5-0.7 ng/mL) were associated with the lowest risk of all-cause mortality (adjusted HR 0.77, 95% CI 0.67-0.89, P < 0.001) while high serum concentrations (1.6-2.0 ng/mL) were associated with increased mortality (adjusted HR 1.33, 95% CI 1.12-1.58, P = 0.001). Consistent with this finding, lower serum concentrations (0.5-0.7 ng/mL) were associated with reduced death from worsening heart failure and a neutral effect on cardiovascular death not due to worsening heart failure. CONCLUSION: These findings favour targeting serum concentrations from 0.5 to 0.7 ng/mL when dosing digoxin in patients with heart failure and reduced EF.

Use of a simplified nomogram to individualize digoxin dosing versus standard dosing practices in patients with heart failure.

STUDY OBJECTIVES: To compare the frequency of achieving a therapeutic serum digoxin concentration (SDC), defined as 0.5-0.9 ng/ml, by using a simplified nomogram to individualize digoxin dosing with standard dosing practices in patients with heart failure, and to characterize the relationship between genetic polymorphisms of the ABCB1 gene and SDC. DESIGN: Prospective study with a historical control group. SETTING: Outpatient care center of an urban academic medical center. PATIENTS: A total of 131 adults with heart failure due to left ventricular dysfunction who were treated with digoxin. INTERVENTION: Digoxin doses were determined either by the dosing nomogram (65 patients) or standard care (SC; 66 patients) by using historical controls who were randomly selected from a list of SDCs obtained from laboratory records and who had their digoxin doses determined by standard dosing practices. MEASUREMENTS AND MAIN RESULTS: The primary end point was the proportion of patients achieving a steady-state SDC of 0.5-0.9 ng/ml; secondary end points were mean SDC and proportion of patients achieving a steady-state SDC lower than 1.0 ng/ml. Postdistributive steady-state SDCs were measured 2-4 weeks after digoxin dosage adjustment or initiation. Therapeutic SDCs were achieved with similar frequency in both groups (38.7% in the nomogram group vs 34.5% in the SC group, p=0.65); however, more patients in the nomogram group had SDCs lower than 1.0 ng/ml than in the SC group (85.0% vs 44.9%, p<0.001). Mean daily digoxin doses were lower in the nomogram group (149 ± 67 µg vs 177 ± 74 µg, p=0.02), resulting in lower mean SDCs compared with those in the SC group (0.52 ± 0.30 ng/ml vs 1.12 ± 0.58 ng/ml, p<0.001). Patients in the pharmacogenetic substudy provided blood samples for genotyping of three common ABCB1 single nucleotide polymorphisms: C1236T (rs1128503), G2677T/A (rs2032582), and C3435T (rs1045642). SDCs were not significantly associated with ABCB1 genotypes. CONCLUSION: Our simplified digoxin dosing nomogram resulted in lower SDCs compared with standard dosing practices but achieved therapeutic SDCs with similar frequency. A greater proportion of patients dosed according to our nomogram had SDCs lower than 1.0 ng/ml, consistent with consensus guidelines. Genetic polymorphisms of the ABCB1 gene were not associated with SDC.

A perspective on re-evaluating digoxin's role in the current management of patients with chronic systolic heart failure: targeting serum concentration to reduce hospitalization and improve safety profile.

Digoxin improves exercise tolerance and reduces hospitalizations in patients with systolic heart failure, but its use has declined progressively for the past two decades. The Digitalis Investigation Group trial showed that digoxin reduced hospitalizations but had a neutral effect on total mortality. There was evidence that mortality caused by worsening heart failure was less, but there was also a signal suggesting an increase in other cardiac (presumed arrhythmic) death. Use of digoxin has declined substantially and recent guideline recommendations have significantly de-emphasized the importance of this drug in the management of heart failure. Two developments suggest that re-evaluation of the contemporary role of digoxin in the management of heart failure with reduced ejection fraction is warranted. First, heart failure remains progressive, characterized by chronic debility, exercise intolerance, and frequent and costly hospitalizations, despite evidence-based drug and device therapies that prolong survival. Health economics have made reducing hospitalizations in patients with heart failure a major priority. Second, a strong association has emerged between serum concentration and the safety and efficacy of digoxin, which indicates a change in our approach to dosing this agent is needed. Experimental and clinical results suggest that optimizing therapeutic benefit and avoiding harm means dosing to achieve low serum digoxin concentrations (0.5-0.9 ng/mL). Digoxin is an inexpensive agent and the totality of evidence indicates that it reduces hospitalizations and improves symptoms safely when dosed to achieve low serum concentrations. These findings suggest digoxin should have a more prominent therapeutic role in patients with heart failure and reduced ejection fraction.

Preparing clinical pharmacy scientists for careers in clinical/translational research: can we meet the challenge?: ACCP Research Affairs Committee Commentary.

Developing clinical pharmacists' research skills and their ability to compete for extramural funding is an important component of the American College of Clinical Pharmacy's (ACCP) vision for pharmacists to play a prominent role in generating the new knowledge used to guide patient pharmacotherapy. Given the recent emphasis on clinical/translational research at the National Institutes of Health (NIH) and the key role of drug therapy in the management of many diseases, there is an unprecedented opportunity for the profession to contribute to this enterprise. A crucial question facing the profession is whether we can generate enough appropriately trained scientists to take advantage of these opportunities to generate the new knowledge to advance drug therapy. Since the 2009 publication of the ACCP Research Affairs Committee editorial recommending the Ph.D. degree (as opposed to fellowship training) as the optimal method for preparing pharmacists as clinical/translational scientists, significant changes have occurred in the economic, professional, political, and research environments. As a result, the 2012 ACCP Research Affairs Committee was charged with reexamining the college's position on training clinical pharmacy scientists in the context of these substantial environmental changes. In this commentary, the potential impact of these changes on opportunities for pharmacists in clinical/translational research are discussed as are strategies for ACCP, colleges of pharmacy, and the profession to increase the number and impact of clinical pharmacy scientists. Failure of our profession to take advantage of these opportunities risks our ability to contribute substantively to the biomedical research enterprise and ultimately improve the pharmacotherapy of our patients.

Observations on the safety and effectiveness of dofetilide in patients with paroxysmal atrial fibrillation and normal left ventricular function.

Dofetilide is currently recommended as second-tier therapy to maintain sinus rhythm in patients with paroxysmal atrial fibrillation (PAF) and normal left ventricular function, yet limited data support this recommendation. We examined the safety and efficacy of dofetilide in this setting through a retrospective chart review. We evaluated patients who had symptomatic PAF, normal left ventricular function, and no significant valvular disease. The end points were complete suppression of symptomatic PAF and subjective symptomatic improvement with dofetilide treatment. Over a 3-year period, 34 patients who had failed previous antiarrhythmic therapy were included. Of these, 3 discontinued dofetilide treatment before discharge. Of the remaining 31 who continued treatment after discharge, it was eventually discontinued in 13. At 12 months, symptomatic improvement was observed in 18 of 31 patients, 6 of whom remained asymptomatic. Treatment with dofetilide in this study was successful in less than 1 in 5 patients. Despite careful precautions, serious proarrhythmias, the major limiting side effect of dofetilide, still occurred during long-term follow-up.

A method of determining the dose of digoxin for heart failure in the modern era.

BACKGROUND: The therapeutic range for digoxin in heart failure has recently changed to become lower and narrower, and the new range is associated with improved mortality. However, dosing methods have not been modified to reflect this change. In this study, we sought to develop a new method to determine the initial dose of digoxin in patients with heart failure. METHODS: Over a 6-month period, medical records were screened and reviewed for hospitalized adult patients who had a steady state digoxin concentration. A multiple linear regression was estimated relating digoxin concentration, digoxin dose, creatinine clearance, and ideal body weight to generate an equation relating the dose of digoxin with these variables and a specific target digoxin concentration of 0.7 ng/mL (0.9 nmol/L). This new method was then compared with 2 existing methods. RESULTS: Included in the study were 54 patients (mean [SD] age, 68 [15] years, with a mean (SD) creatinine clearance of 50 (25) mL/min (0.8 [0.4] mL/s) and mean (SD) ideal body weight of 62 (11) kg. Our proposed method and the Jusko and Koup method were more accurate than the Jelliffe method in predicting digoxin concentration. Root mean square errors were as follows: for the Jelliffe method (using ideal body weight), 0.810; for the Koup and Jusko method (with heart failure), 0.401; our proposed method, 0.375. The proposed method was then used to create a dosing nomogram. CONCLUSIONS: Because the new therapeutic window of digoxin is associated with improved outcomes, more intensive dosage refinement should be considered. To this end, we offer new dosing recommendations and a nomogram for determining the initial dose of digoxin in patients with heart failure.

Mechanisms, manifestations, and management of digoxin toxicity in the modern era.

Because of the common use of digoxin and because of its narrow therapeutic index, digoxin toxicity has been prevalent historically and, therefore, most clinicians are well aware of the classical dose/concentration-related signs and symptoms of toxicity. Yet, in the modern era the incidence of digoxin toxicity has been declining for a variety of reasons, including a new (lower) therapeutic range, the development of more effective drug therapies for heart failure, and more accurate dosing methods. In addition, digoxin toxicity, once commonly fatal, can now be quickly and effectively treated by the emergency administration of antidigoxin Fab fragments. Indeed, it may be possible to expand the use of Fab fragments to select patients with non-life-threatening digoxin toxicity, in order to save costs and improve patient comfort. Most cases of digoxin toxicity are caused by inappropriately high dosages, which are usually prescribed in the setting of renal dysfunction, while other cases can be attributed to system errors such as multiple prescriptions, poor patient counseling, or errors in transcribing. With modern computerized prescribing systems, such as direct physician order entry and prompts that alert the clinician to the potential for error, it is possible to decrease the incidence of digoxin toxicity even further. A realistic goal is to nearly eradicate once commonplace digoxin toxicity or at least make its occurrence a rare event.