Effect of aging on the incidence of digoxin toxicity

Expert Consensus on the Diagnosis and Management of Digoxin Toxicity

While there has been a decline in the use of digoxin in patients with heart failure and atrial fibrillation, acute and chronic digoxin toxicity remains a significant clinical problem. Digoxin's narrow therapeutic window and nonspecific signs and symptoms of toxicity create clinical challenges and uncertainty around the diagnostic criteria of toxicity and responsive treatment choices for the bedside clinician. A systematic review of published literature on digoxin toxicity (34,587 publications over 6 decades, with 114 meeting inclusion criteria) was performed to develop 33 consensus statements on diagnostic and therapeutic approaches which were then evaluated through a modified Delphi process involving a panel of experts in cardiology, nursing, emergency medicine, and medical toxicology. The results demonstrate agreement about the need to consider time of ingestion and nature of the exposure (ie, acute, acute-on-chronic, chronic) and the use of digoxin immune Fab for life-threatening exposure to decrease risk of death. While several areas of continued uncertainty were identified, this work offers formalized guidance that may help providers better manage this persistent clinical challenge.

Population pharmacokinetic analysis and dosage recommendations for digoxin in Japanese patients with atrial fibrillation and heart failure using real-world data

BACKGROUND

Digoxin is an important treatment option for reducing the ventricular rate in patients with atrial fibrillation (AF) and heart failure (HF). Digoxin has a narrow therapeutic window and large interindividual variability. A low target blood concentration, especially ≤0.9 ng/mL, is recommended for patients with HF who are taking digoxin. This study aimed to develop a population pharmacokinetic model and to identify clinical factors that affect digoxin exposure and an optimal digoxin dosing regimen in Japanese patients with AF and HF.

METHODS

A population pharmacokinetic analysis was performed by using a nonlinear mixed effects model based on 3465 concentration points from 391 patients (>18 years) who were receiving oral digoxin. Using trough serum digoxin concentrations and clinical data, a population pharmacokinetic model was developed for determining covariates of clearance. A 1-compartment model was used to examine the interindividual variability of the oral clearance (CL/F) of digoxin. An appropriate dosage of digoxin was identified using Monte Carlo simulation.

RESULTS

The final model demonstrated that creatinine clearance (CL_CR) and the use of amiodarone were factors that contributed to the CL/F of digoxin. Monte Carlo simulation results showed that with a daily maintenance dose of 0.25 mg, the intoxication risk window of a trough serum concentration of ≥0.9 ng/mL could be reached in more than half of patients regardless of renal function category or concurrent use of amiodarone. The appropriate maintenance dosage was 0.125 mg daily for most Japanese patients with AF and HF. However, with a daily dose of 0.125 mg, a trough serum concentration of ≥0.9 ng/mL could be reached in more than half of patients with renal impairments (CL_CR 30 mL/min) or concurrent use of amiodarone. A daily maintenance dose of 0.0625 mg was acceptable for these patients.

CONCLUSIONS

CL_CR and the use of amiodaron were found to contribute to digoxin clearance using a population pharmacokinetic methodology. For Japanese patients with AF and HF, 0.125 mg is an appropriate daily digoxin maintenance dose, but a dose reduction is required for patients with CL_CR <30 mL/min or concurrent amiodarone use.

Cardiac glycosides display selective efficacy for STK11 mutant lung cancer

Although STK11 (LKB1) mutation is a major mediator of lung cancer progression, targeted therapy has not been implemented due to STK11 mutations being loss-of-function. Here, we report that targeting the Na⁺/K⁺-ATPase (ATP1A1) is synthetic lethal with STK11 mutations in lung cancer. The cardiac glycosides (CGs) digoxin, digitoxin and ouabain, which directly inhibit ATP1A1 function, exhibited selective anticancer effects on STK11 mutant lung cancer cell lines. Restoring STK11 function reduced the efficacy of CGs. Clinically relevant doses of digoxin decreased the growth of STK11 mutant xenografts compared to wild type STK11 xenografts. Increased cellular stress was associated with the STK11-specific efficacy of CGs. Inhibiting ROS production attenuated the efficacy of CGs, and STK11-AMPK signaling was important in overcoming the stress induced by CGs. Taken together, these results show that STK11 mutation is a novel biomarker for responsiveness to CGs. Inhibition of ATP1A1 using CGs warrants exploration as a targeted therapy for STK11 mutant lung cancer.

Retrospective evaluation of patients with elevated digoxin levels at an emergency department

Objectives

We investigated the demographic characteristics, clinical and laboratory findings, treatment strategies and clinical outcomes of patients presenting at emergency department (ED) with digoxin levels at or above 1.2 ng/ml.

Materials and methods

The demographic and clinical characteristics of patients with serum digoxin levels at or above 1.2 ng/ml admitted to an ED between January 2010 and July 2011 were investigated in this cross-sectional descriptive study. Patients with ECG and clinical findings consistent with digoxin toxicity and no additional explanation of their symptoms were evaluated for digoxin toxicity.

Results

In this study 137 patients were included, and 68.6% of patients were women with mean age 76.1 ± 12.2. There was no significant difference between gender and digoxin intoxication. The mean age of intoxicated group was significantly higher than the non-intoxicated group (P = 0.03). The most common comorbidities were congestive heart failure (n = 91) and atrial fibrillation (n = 74). The most common symptoms were nausea, vomiting and abdominal pain. The levels of hospitalization and mortality in this group were significantly higher.

Conclusion

Digoxin intoxication must be suspected in patients present in the ED, particularly those with complaints that include nausea and vomiting, as well as new ECG changes; serum digoxin levels must be determined.

Emergency department visits and hospitalizations for digoxin toxicity: United States, 2005 to 2010

BACKGROUND

Recent data on digoxin prescribing and adverse events are lacking but could help inform the management of digoxin in contemporary heart failure treatment.

METHODS AND RESULTS

We determined nationally representative numbers and rates of emergency department (ED) visits for digoxin toxicity in the United States using 2005 to 2010 reports from the National Electronic Injury Surveillance System-Cooperative Adverse Drug Event Surveillance project and the National Ambulatory (and Hospital Ambulatory) Medical Care Surveys. Based on 441 cases, an estimated 5156 (95% confidence interval [CI], 2663-7648) ED visits for digoxin toxicity occurred annually in the United States; more than three fourths (78.8% [95% CI, 73.5%-84.1%]) resulted in hospitalization. Serum digoxin level was ≥2.0 ng/mL for 95.8% (95% CI, 93.2%-98.4%) of estimated ED visits with levels reported (n=251 cases). The rate of ED visits per 10 000 outpatient prescription visits among patients≥85 years was twice that of patients 40 to 84 years (rate ratio, 2.4 [95% CI, 1.2-5.0]); among women, the rate was twice that of men (rate ratio, 2.3 [95% CI, 1.1-4.7]). Digoxin toxicity accounted for an estimated 1.0% (95% CI, 0.6%-1.4%) of ED visits for all adverse drug events among patients≥40 years, but an estimated 3.3% (95% CI, 2.3%-4.4%) of ED visits and 5.9% (95% CI, 4.0%-7.9%) of hospitalizations for all adverse drug events among patients≥85 years. Estimated annual ED visits and hospitalizations remained relatively constant from 2005 to 2010.

CONCLUSIONS

Digoxin toxicity is not declining; more careful prescribing to high-risk groups and improved monitoring of serum levels might be needed to reduce morbidity from outpatient digoxin use.

Contemporary Considerations for the Use of Digoxin for Heart Failure in Older Patients

Background:

Digoxin has been used in older people for over 200 years to treat heart failure. Research over the past 15 years has caused the place of digoxin in therapy to evolve. This review was conducted in order to describe the role of digoxin in the care of older patients with heart failure.

Methods:

This review was conducted by systematically searching the literature using MEDLINE via Ovid, Cochrane Library, Pub Med and EMBASE, with the search terms “heart failure” and “digoxin.” Studies published after publication of the Digitalis Investigation Group (DIG) trial (conducted from February 1997 to October 2010) were selected for possible inclusion in the review.

Results:

The majority of data regarding the use of digoxin for heart failure in older people originates from the DIG trial and the various post-hoc analyses of this dataset. When considered in unison with evidence for other heart failure therapies (e.g., angiotensin-converting enzyme inhibitors), the place of digoxin is clear, in that it should be used for patients in sinus rhythm who are symptomatic despite therapy with first-line agents or for those with concomitant atrial fibrillation whose heart rate is not well controlled by, or cannot tolerate, beta-adrenergic blockers. There are various safety and monitoring parameters that should be considered in older people when using this drug.

Conclusions:

Digoxin is a drug that still demonstrates value for heart failure in older patients when used appropriately, and after first-line agents have been maximized.

Digoxin therapy in the elderly: pharmacokinetic considerations in nursing

Digoxin is effective in controlling ventricular rhythm in atrial fibrillation and is used in heart failure when angiotensin converting enzyme inhibitors and diuretics are ineffective. Because use of more than 1 drug is often required with these conditions, pharmacokinetic considerations, including those related to complementary medicine, are important. Increased awareness of drug action in the elderly is important because there is often an increase in body fat and leaner muscle mass as well as changes in organ function, such as that of the kidney, which alters drug activity. Nurses have an important role to play in the safe administration of digoxin.

Predicting heart failure mortality in frail seniors: comparing the NYHA functional classification with the Resident Assessment Instrument (RAI) 2.0

BACKGROUND

Though the NYHA functional classification is recommended in clinical settings, concerns have been raised about its reliability particularly among older patients. The RAI 2.0 is a comprehensive assessment system specifically developed for frail seniors. We hypothesized that a prognostic model for heart failure (HF) developed from the RAI 2.0 would be superior to the NYHA classification. The purpose of this study was to determine whether a HF-specific prognostic model based on the RAI 2.0 is superior to the NYHA functional classification in predicting mortality in frail older HF patients.

METHODS

Secondary analysis of data from a prospective cohort study of a HF education program for care providers in long-term care and retirement homes. Univariate analyses identified RAI 2.0 variables predicting death at 6 months. These and the NYHA classification were used to develop logistic models.

RESULTS

Two RAI 2.0 models were derived. The first includes six items: "weight gain of 5% or more of total body weight over 30 days", "leaving 25% or more food uneaten", "unable to lie flat", "unstable cognitive, ADL, moods, or behavioural patterns", "change in cognitive function" and "needing help to walk in room"; the C statistic was 0.866. The second includes the CHESS health instability scale and the item "requiring help walking in room"; the C statistic was 0.838. The C statistic for the NYHA scale was 0.686.

CONCLUSIONS

These results suggest that data from the RAI 2.0, an instrument for comprehensive assessment of frail seniors, can better predict mortality than the NYHA classification.

Beers-Fick criteria and drugs available through the Farmácia Dose Certa program

CONTEXT AND OBJECTIVE

Farmácia Dose Certa is a program available in the State of São Paulo that is a national reference for providing drugs free of charge to the population. Elderly people receiving care deserve special attention regarding drugs that are appropriate for their age group. The objective was to assess the drugs in the program considered to be inappropriate for the elderly.

DESIGN AND SETTING

Descriptive study evaluating free drug distribution in the State of São Paulo, Brazil.

METHODS

Following the criteria proposed by Beers and Fick (drugs or drug classes that should be avoided among elderly people, independent of the diagnosis or clinical condition, because of the high risk of side effects and because other, safer drugs are available), the drugs in the Farmácia Dose Certa program that might be inappropriate for elderly people and the levels of evidence for each drug included were assessed.

RESULTS

Among the available drugs, 10 (25.6%) were included within the Beers-Fick criteria. The drugs selected were: amitriptyline, cimetidine, diazepam, digoxin, fluoxetine, methyldopa, nifedipine, promethazine, thioridazine and ferrous sulfate.

CONCLUSION

The list of drugs available within the Farmácia Dose Certa program may be considered appropriate for the general population, but not completely for the elderly population. Adjusting this list to the pharmacological aspects of aging will reduce the risks of drug interactions, falls, mental confusion and excessive sedation that result from drugs that are considered inappropriate for consumption by elderly people.

Clinical manifestations of elderly patients with digitalis intoxication in the emergency department

This study aimed to determine the clinical characteristics of elderly patients diagnosed with digitalis intoxication, on the Emergency Department, University Hospital Complex, A Coruña, Spain. During the study period (January-September 2008) cases were included in which digitalis intoxication was confirmed by plasma digoxin levels. We collected data on age, gender, base-line diseases, therapeutic indications for digoxin, functional classification, ejection fraction, plasma digoxin levels, creatinine clearance, ions, gasometry, electrocardiogram, concomitant medication, symptomatology and treatment. The results were: mean age 82.0 ± 6.6 years, predominantly female subjects (83.7%). The most prevalent pathologies were cardiac valvulopathy (81.0%), hypertension (68.3%) and ischemic cardiopathy (46.3%), 95.1% had a background of cardiac insufficiency, and 52.6% were in functional grade III. The mean digoxin level was 2.7 ± 0.69 ng/ml, 23.1% of the patients had a creatinine clearance of less than 60 ml/min/1.73 m(2) and 2.6% had a severely reduced glomerular filtration rate (GFR) (clearance<30 ml/min/1.73 m(2)). A negative correlation was found between digoxin levels and clearance (r = -0.22; p = 0.18) and between the levels and cardiac frequency (r = -0.35; p = 0.026). Of the patients, 47.5% presented bradycardia and 87.8% arrhythmias, most frequently auricular fibrillation. The most frequent symptoms were nausea (54.8%), fatigue (42.9%), vomiting (33.3%) and anorexia (28.6%). We conclude that clinical digestive symptoms in elderly women who are taking digitalis, with bradycardia and impaired renal functioning, should lead us to suspect digitalis intoxication.

Alternatives for Potentially Inappropriate Medications in the Elderly Population: Treatment Algorithms for Use in the Fleetwood Phase III Study

OBJECTIVE

To provide estimates of the prevalence of potentially inappropriate medications used in eligible nursing facilities, to describe the development of evidence-based treatment algorithms for recommending safer alternative treatments to potentially inappropriate medications, and to provide the actual treatment algorithms developed for the Fleetwood Phase III study.

DESIGN

Literature review, cross-sectional design.

SETTING

Thirty North Carolina nursing facilities eligible for Fleetwood Phase III.

PATIENTS, PARTICIPANTS

Algorithms developed for use by all pharmacists in the long-term care pharmacy serving the intervention facilities site for the Fleetwood Phase III study.

INTERVENTIONS

Pharmacists are prospectively intervening directly with the prescriber to recommend a safer alternative to inappropriate medications using the standardized treatment algorithms developed for the study.

MAIN OUTCOME MEASURE(S)

Prevalence of potentially inappropriate medications used among residents and the development of 14 treatment algorithms suggesting appropriate alternatives to inappropriate medications.

RESULTS

The percentage of potentially inappropriate medications used ranged from 0% to 13.2% at baseline in March 2002. We also found that evidence-based treatment algorithms were well received by consultant pharmacists at the intervention sites of the Fleetwood Phase III study.

CONCLUSION

We have provided prevalence rates of potentially inappropriate medication use in nursing homes and developed treatment algorithms for pharmacists to use when making clinical recommendations regarding safer alternatives to potentially inappropriate medications in the elderly population. We are in the process of evaluating the effect of pharmacists' prospective interventions by using these standardized evidence-based treatment algorithms to reduce the prevalence of inappropriate medication use in intervention facilities.

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.

Declining public health burden of digoxin toxicity from 1991 to 2004

We hypothesized that digoxin toxicity has declined in recent years, and that the decline is accompanied by reductions in overall utilization and dose. To analyze trends in digoxin toxicity and utilization from 1991 to 2004, we used surveys from the National Center for Health Statistics and Medicaid data in the United States and The Health Improvement Network (THIN) database in the United Kingdom. There was a significant decline in digoxin toxicity hospitalizations in the United States and a decline in ambulatory digoxin toxicity in the United Kingdom. The study demonstrated a reduction in the use of digoxin in the United States, but found no change in digoxin use in the United Kingdom. Finally, the number of prescriptions written for at least 250 microg decreased in the United States and the United Kingdom. The public health burden of digoxin toxicity declined dramatically from 1991 to 2004 in the United Kingdom and the United States.

Pharmacokinetic-Pharmacodynamic Crisis in the Elderly

Advances in medical technology have led to improved survival after catastrophic illnesses. Many of the survivors require ongoing care including tracheostomy, mechanical ventilation, tube feedings, and indwelling venous catheters. Repeated hospitalizations may be necessary to treat infectious complications resulting from resistant organisms requiring intravenous antibiotic therapy. Because prolonged intravenous access may be difficult or even impossible in these patients, alternative means of therapy are necessary. Linezolid is the first of a new class of antimicrobial agents known as the oxazolidinones with activity against gram-positive bacteria similar to that of vancomycin and yet its oral bioavailability allows for enteral administration. We present our retrospective experience with oral linezolid in a cohort of pediatric intensive care unit patients. Primary infectious disease issues included endocarditis, tracheitis, pneumonia, or central line sepsis resulting from Staphylococcus epidermidis, methicillin-resistant Staphylococcus aureus, and Enterococcus. Treatment was initiated with vancomycin and changed to enteral linezolid (10 mg/kg every 12 hours). The duration of therapy with linezolid varied from 7 days to 6 weeks. All of the patients were discharged home to complete their course of enteral linezolid. No complications related to linezolid therapy were noted, and all of the patients completed their prescribed course of therapy without the need for rehospitalization. Our preliminary experience suggests that oral linezolid offers an effective alternative to intravenous vancomycin for the treatment of infections resulting from gram-positive bacteria and avoids the need for prolonged vascular access.

Age-related differences in the prevalence of potential drug-drug interactions in ambulatory dyslipidaemic patients treated with statins

BACKGROUND AND OBJECTIVE

Elderly patients may be at higher risk of drug-drug interactions (DDIs) because of polypharmacy. This study evaluated age-specific differences in the prevalence of clinically relevant potential DDIs (pDDIs) in ambulatory dyslipidaemic patients treated with an HMG-CoA reductase inhibitor (statin). We hypothesised that elderly patients are at higher risk for pDDIs because of the presence of more drugs and drugs with a higher potential for DDIs in this age group.

METHODS

A total of 2742 dyslipidaemic ambulatory patients treated with a statin were included in this cross-sectional study. Drug treatment was screened for clinically relevant pDDIs using an electronic drug interaction program (DRUG-REAX System).

RESULTS

The study sample consisted of 483 (17.6%) patients aged < or = 54 years, 732 (26.7%) aged 55-64 years, 924 (33.7%) aged 65-74 years and 603 (22.0%) patients aged > or = 75 years. Patients > or =75 years had significantly more pharmacologically active substances prescribed than patients aged < or =54 years (mean 5.8 vs 3.8, respectively; p < 0.001). Cardiovascular diseases such as coronary heart disease, heart failure or arrhythmias were also significantly more prevalent in patients aged > or = 75 years than in younger patients. The overall prevalence of pDDIs increased significantly from 7.9% in those aged < or = 54 years to 18.4% in patients aged > or = 75 years (p < 0.001). The frequency of both pDDIs associated with statins and non-statin pDDIs increased with age. Risk factors for pDDIs in patients aged > or = 75 years were arrhythmias, heart failure and the number of pharmacologically active substances prescribed. The more frequent prescription of cardiovascular drugs with a high potential for pDDIs (e.g. amiodarone and digoxin) in patients aged > or = 75 years was mainly responsible for the observed increases in statin and non-statin pDDIs in this age group.

CONCLUSIONS

Compared with younger patients, elderly dyslipidaemic patients are at a higher risk for clinically relevant pDDIs, mainly because of a higher number of drugs prescribed. In addition, patients aged > or = 75 years were prescribed more drugs with a high potential for DDIs, especially drugs used for the treatment of arrhythmias and heart failure. The risk for adverse reactions associated with pDDIs may often be reduced by dose adjustment, close monitoring or selection of an alternative drug.

[Cognitive impairment induced by digoxin intake in patients older than 65 years]

Cognitive impairment or clinical signs of dementia in an old patient who receives digoxin, should suggest a digitalis intoxication. Symptoms can be present although a normal digoxin serum concentration. It is recommended to stop the treatment to obtain a regression of dementia symptoms.

Is inappropriate medication use a major cause of adverse drug reactions in the elderly?

AIM

To study the occurrence of adverse drug reactions (ADRs) linked to inappropriate medication (IM) use in elderly people admitted to an acute medical geriatric unit.

METHODS

All the elderly people aged > or = 70 years admitted to the acute medical geriatric unit of Limoges University hospital (France) over a 49-month period were included, whatever their medical condition. For all the patients, clinical pharmacologists listed the medications given before admission and identified the possible ADRs. The appropriateness of these medications and the causal relationship between drugs (either appropriate or not) and ADRs were evaluated.

RESULTS

Two thousand and eighteen patients were included. The number of drugs taken was 7.3 +/- 3.0 in the patients with ADRs and 6.0 +/- 3.0 in those without ADRs (P < 0.0001). Sixty-six percent of the patients were given at least one IM prior to admission. ADR prevalence was 20.4% among the 1331 patients using IMs and 16.4% among those using only appropriate drugs (P < 0.03). In only 79 of the 1331 IM users (5.9%) were ADRs directly attributable to IMs. The IMs most often involved in patients with ADRs were: anticholinergic antidepressants, cerebral vasodilators, long-acting benzodiazepines and concomitant use of two or more psychotropic drugs from the same therapeutic class. Using multivariate analysis, after adjusting for confounding factors, IM use was not associated with a significant increased risk of ADRs (odds ratio 1.0, 95% confidence interval 0.8, 1.3).

CONCLUSION

Besides a reduction in the number of drugs given to the elderly, a good prescription should involve a reduction in the proportion of IMs and should take into consideration the frailty of these patients.

Canadian Cardiovascular Society consensus conference recommendations on heart failure 2006: diagnosis and management

Heart failure remains a common diagnosis, especially in older individuals. It continues to be associated with significant morbidity and mortality, but major advances in both diagnosis and management have occurred and will continue to improve symptoms and other outcomes in patients. The Canadian Cardiovascular Society published its first consensus conference recommendations on the diagnosis and management of heart failure in 1994, followed by two brief updates, and reconvened this consensus conference to provide a comprehensive review of current knowledge and management strategies. New clinical trial evidence and meta-analyses were critically reviewed by a multidisciplinary primary panel who developed both recommendations and practical tips, which were reviewed by a secondary panel. The resulting document is intended to provide practical advice for specialists, family physicians, nurses, pharmacists and others who are involved in the care of heart failure patients. Management of heart failure begins with an accurate diagnosis, and requires rational combination drug therapy, individualization of care for each patient (based on their symptoms, clinical presentation and disease severity), appropriate mechanical interventions including revascularization and devices, collaborative efforts among health care professionals, and education and cooperation of the patient and their immediate caregivers. The goal is to translate best evidence-based therapies into clinical practice with a measureable impact on the health of heart failure patients in Canada.

The Influence of Cardiovascular Physiology on Dose/Pharmacokinetic and Pharmacokinetic/Pharmacodynamic Relationships

Inter- and intraindividual variability in the relationship between dose and clinical--or pharmacodynamic--response of a drug can be analysed in two steps: firstly, by considering the plasma pharmacokinetic response to a given dose and, secondly, by the connection between both pharmacokinetic and pharmacodynamic responses. As the cardiovascular system is the means of transport of endogenous and exogenous substances, blood flow fraction destined to each organ determines the relative mass of solute in plasma, which is constantly in contact with the tissue. Hence, not only the rate but also the extent of drug transfer would be increased when tissues are irrigated by a higher fraction of cardiac output. Aging and circadian rhythms present similar cardiac output distribution patterns when moving from young to aged adult and from nocturnal to diurnal hours. These two changes lead to an increased blood flow delivery to the extra-splanchnic-renal region in the elderly and in the morning, but with a decreased cardiac output in aged individuals and an increased one during the day. This scenario allows us to forecast substance concentrations outside the blood vessels, which are responsible for the extent of drug elimination and the intensity of drug effect. So available data on disposition and pharmacodynamics of drugs might be explained from another point of view that challenges current knowledge. Furthermore, the administration of cardiovascular active drugs might reverse the chronological sequence between pharmacokinetic and pharmacodynamic responses, since they could modify blood flow distribution.

Aging biology and geriatric clinical pharmacology

Population aging evokes doomsday economic and sociological prognostication, despite a minority of older people suffering significant dependency and the potential for advances in therapeutics of age-related disease and primary aging. Biological aging processes are linked mechanistically to altered drug handling, altered physiological reserve, and pharmacodynamic responses. Parenteral loading doses need only be adjusted for body weight as volumes of distribution are little changed, whereas oral loading doses in some cases may require reduction to account for age-related increases in bioavailability. Age-related reduction of hepatic blood flow and hepatocyte mass and primary aging changes in hepatic sinusoidal endothelium with effects on drug transfer and oxygen delivery reduce hepatic drug clearance. Primary renal aging is evident, although renal clearance reduction in older people is predominantly disease-related and is poorly estimated by standard methods. The geriatric dosing axiom, "start low and go slow" is based on pharmacokinetic considerations and concern for adverse drug reactions, not from clinical trial data. In the absence of generalizable dosage guidelines, individualization via effect titration is required. Altered pharmacodynamics are well documented in the cardiovascular system, with changes in the autonomic system, autacoid receptors, drug receptors, and endothelial function to modify baseline cardiovascular tone and responses to stimuli such as postural change and feeding. Adverse drug reactions and polypharmacy represent major linkages to avoidable morbidity and mortality. This, combined with a deficient therapeutic evidence base, suggests that extrapolation of risk-benefit ratios from younger adults to geriatric populations is not necessarily valid. Even so, therapeutic advances generally may convert healthy longevity from an asset of fortunate individuals into a general social benefit.

Inappropriate use of digoxin in older hospitalized heart failure patients

BACKGROUND

Older adults are more likely to suffer from the adverse effects of digoxin. Studies have described the inappropriate use of digoxin in various populations. The objective of this study was to determine the correlates of inappropriate digoxin use in older heart failure patients.

METHODS

We studied older hospitalized heart failure patients with documented left ventricular (LV) function evaluation and electrocardiography. Digoxin use was considered inappropriate if patients had preserved LV systolic function (ejection fraction greater > or =40%) or if they had no atrial fibrillation (AF). We compared baseline patient characteristics by indication for digoxin and tested statistical significance using Pearson's chi-square analysis and Student's t tests. Using logistic regression, we determined the correlates of inappropriate use and initiation of digoxin.

RESULTS

Subjects (N = 603) had a mean age of 79 (+/-7) years; 59% were women, and 18% were African American. A total of 376 patients (62%) were discharged on digoxin, and 223 (37%) had no indication for its use. Half of the patients without an indication for digoxin received the drug. Of 132 patients without an indication and not already on digoxin, 38 (29%) were initiated on it. After adjustment for various patient and care characteristics, prior digoxin use (adjusted odds ratio [OR] 11.47, 95% confidence interval [CI] 5.72-23.02) and pulse > or =100/min (adjusted OR 2.33, 95% CI 1.10-4.94) were associated with inappropriate digoxin use. Pulse > or =100/min was also associated with inappropriate initiation of the drug (adjusted OR 2.95, 95% CI 1.28-6.78).

CONCLUSIONS

Inappropriate use of digoxin was common and was associated with prior use. Tachycardia was associated with inappropriate use and initiation. Electrocardiography and echocardiography should be performed in all older heart failure patients. Digoxin therapy should not be initiated or continued in patients without any evidence of LV systolic dysfunction or chronic AF.

Cognitive toxicity of drugs used in the elderly

The aged are an extremely heterogeneous population that is growing worldwide, included are healthy and agile individuals in their early sixties, as well as an increasing number of people over the age of 35. Pharmacotherapy is expected to continue its prominent role in the medical management of a wide range of conditions that affect older people. Adverse consequences of all kinds complicate the use of medications, and such events seem to increase in incidence with polypharmacy. Cognitive impairment can occur during the course of treatment with a wide range of medications and can have a variety of presentations, Both the number of concurrent medications that older individuals routinely use and physiologic changes in these patients render them more susceptible to developing cognitive toxicity. Most of the frequently implicated medications carry documentation of their ability to cause cognitive disturbances in their package labeling, suggesting that the level of vigilance for adverse effects during the course of their use should always be high. Such caution can be used to guide appropriate drug treatment of the aged so that clinicians do not need to opt for undertreatment to avoid toxicity.