Digoxin toxicity in the aged. Characterising and avoiding the problem

Recent Updates on Risk and Management Plans Associated with Polypharmacy in Older Population

The concept of polypharmacy encompasses adverse drug reactions and non-adherence factors in elderly individuals. It also leads to the increased use of healthcare services and negative health outcomes. The problem is further alleviated by the odds of potentially inappropriate medications (PIM), which lead to the development of drug-related problems. Since polypharmacy is more commonly observed in the elderly population, urgency is required to introduce operative protocols for preventing and managing this problem. The family medicine model of care can be associated with favorable illness outcomes regarding satisfaction with consultation, treatment adherence, self-management behaviors, adherence to medical advice, and healthcare utilization. Hence, interventions built on family medicine models can provide significant support in improving the outcomes of the older population and their quality of life. In this regard, the authors have taken up the task of explaining the accessible resources which can be availed to improve the application of health care services in the field of geriatric medicine.

Efficiency of individual dosage of digoxin with calculated concentration

Background

Digoxin is a frequently prescribed drug, particularly in the elderly population, in which there is an increased prevalence of atrial fibrillation and cardiac failure. With its complex pharmacokinetic profile and narrow therapeutic index, use of digoxin requires regular monitoring of blood levels. Recent evidence suggests that a lower concentration range (0.4–1.0 ng/mL) is preferable in patients with congestive heart failure and a higher range (0.8–2.0 ng/mL) is needed in patients with atrial tachyarrhythmia. The Konishi equation is widely used to predict the serum digoxin concentration (SDC) in Japan. This study assessed the correlation between SDC predicted by the Konishi equation and that actually measured in Chinese patients and investigated the impact of renal function on SDC.

Methods

The study subjects comprised 72 patients with cardiac failure or/and atrial tachyarrhythmia seen at our hospital from January 2012 to December 2013. The patients were divided into five groups according to Kidney Diseases Outcome Quality Initiative guidelines. SDCs were measured using the Abbott Architect i1000 immunology analyzer. The correlations between measured SDCs and calculated SDCs and between clearance of digoxin and creatinine clearance rate were assessed retrospectively.

Results

The correlation between measured and predicted SDC calculated by the Konishi equation was significant (r=0.655, P<0.001) for the 72 patients overall; however, correlations within the different stages of renal function were nonsignificant, with a correlation found only in patients with stage 3 (30 mL per minute < creatinine clearance <60 mL per minute). With regard to the correlation between clearance of digoxin and creatinine clearance, our results show that although there was a significant correlation between clearance of digoxin and creatinine clearance in the group overall, correlations were not evident within the different stages of renal function.

Conclusion

The results of this study indicate that clearance of digoxin and the creatinine clearance rate cannot be explained by renal function alone and that the validity of the Konishi equation for individualizing the digoxin dosage in Chinese patients is limited, being applicable only in stage 3 renal disease. Further research in larger numbers of patients across all stages of renal function will be required in the future to verify the original Konishi model.

The 3 D's of geriatric psychiatry: depression, delirium, and dementia

A Caucasian female octogenarian with multiple medical problems was admitted to the inpatient geriatric psychiatry unit with intermittent altered mental status and decline in memory. She had been hospitalized four times in the previous three months. She was admitted on more than 10 medications and received more than 20 different medications in this time period. It was determined that she had delirium concurrent with dementia and/or depression. During her hospital stay a urinary tract infection (UTI) was treated, her anticholinergic medications were minimized, and her digoxin dose was adjusted. As her mental status cleared, a workup was completed to differentiate between dementia and depression. She was initially treated with memantine, but as time progressed it became more evident she was experiencing depression and a "pseudodementia," which was treated with sertraline. Her Mini-Mental State Examination returned to 29/30 (her score previously was 26/29). This case demonstrates the complexity of treating an elder individual and the importance of differentiating among delirium, depression, and dementia. The pharmacy team played an active role in medication reconciliation. Additionally, they worked with the medical team to minimize her potentially harmful medications and optimize the treatment of her UTI and depression.

Pharmacokinetic considerations for digoxin in older people

OBJECTIVE

This review aims to arm readers with a deep understanding of pharmacokinetics of digoxin.

DATA SOURCES

Pharmacology and pharmacokinetic references texts, and peer reviewed medical journal manuscripts indexed on Medline included based on currency, accuracy and appropriateness.

RESULTS

Physiologic changes and disease associated with aging have an impact on pharmacokinetics and pharmacodynamics of medications. Altered drug response and increased adverse reactions are common amongst the elderly. The narrow therapeutic index of digoxin and pharmacokinetic changes associated with aging increases the risk of toxicity. In the aging population, a number of factors combine to increase the risk, severity and likelihood of hospitalisation or death due to adverse drug effects: changes to absorption, distribution, metabolism and excretion,increased susceptibility to drug sensitivity,co-existing pathology,polypharmacy.

CONCLUSION

A thorough understanding of digoxin pharmacokinetics in the older person is essential for improved therapeutic outcomes, improved compliance, reduced morbidity and improved quality of life.

The association of ABCB1 polymorphisms and elevated serum digitoxin concentrations in geriatric patients

OBJECTIVE

Digitoxin is a known substrate of the efflux pump P-glycoprotein (gene name: ABCB1). P-glycoprotein expression was shown to be modulated by single nucleotide polymorphisms in the ABCB1 gene, but it remains unclear whether these polymorphisms influence digitoxin blood levels. Our objective was to examine the association of ABCB1 C3435T genotype and elevated serum digitoxin concentrations (SDC) in a cohort of 77 geriatric patients consecutively admitted to a geriatric department over a 12-month period.

METHODS

The impact of ABCB1 3435 CC, CT, and TT genotypes on SDC and SDC normalized for daily digitoxin dosage and body weight was assessed by multivariate regression analysis.

RESULTS

Among participants, 18 (23%) had the CC, 36 (47%) the CT, and 23 (30%) the TT genotype. Adjusting for relevant covariates, no significant association of ABCB1 C3435T genotype and SDC or normalized SDC was detected. Mean SDC was 22.4 ng/ml (95% CI 18.9-25.9) for the TT, 21.8 ng/ml (95% CI 18.1-25.5) for the CT, and 25.7 ng/ml (95% CI 20.6-30.8) for the CC genotype. The means for normalized SDC were 5.2 kg.l(-1) (95% CI 4.3-6.1) for the TT, 6.1 kg.l(-1) (95% CI 4.7-7.5) for the CT, and 6.2 kg.l(-1) (95% CI 4.6-7.7) for the CC genotype.

CONCLUSION

In this sample of frail geriatric patients, the impact of ABCB1 C3435T genotype on serum digitoxin concentration was not of major relevance. Regular monitoring of digitoxin blood levels and surveillance of appropriate drug use remain the best ways to prevent digitoxin intoxications in the elderly.

Use of cardiovascular medications in the elderly

Cardiovascular disease is the leading cause of death in patients aged 65 and above. Although elderly persons represent only 12.4% of the US population, they account for about a third of drug expenditures. However the appropriate use of cardiovascular medications in these patients has been shown to reduce the rate of cardiovascular morbidity and mortality. The normal aging and the disease process in the elderly result in significant changes at the structural and molecular level in the elderly. The changes that take place in the autonomic nervous system, the kidneys, and the liver in the elderly modify the metabolism and clinical effects of most medications. Elderly patients are also susceptible to side effects and adverse drug reactions. Physicians should have a clear understanding of the normal aging processes, the abnormal changes due to disease process and the changes in the pharmacology of drugs in the elderly to deliver proper care to the elderly patient.

Cilomilast: pharmacokinetic and pharmacodynamic interactions with digoxin

BACKGROUND

Cilomilast is an orally active, selective phosphodiesterase 4 inhibitor currently in clinical development for the treatment of chronic obstructive pulmonary disease.

OBJECTIVE

The purpose of this study was to examine the tolerability and steady-state pharmacokinetics of cilomilast and digoxin when coadministered at standard therapeutic doses in healthy adults.

METHODS

In an initial, open-label phase, healthy young adults received cilomilast 15 mg BID for 5 days. After a 7-day washout period, subjects entered a double-blind, crossover phase during which they received oral digoxin (375 microg once daily) for 2 consecutive 14-day periods with no intervening washout period. Cilomilast 15 mg BID or placebo was coadministered during the first 14-day period. Subjects then crossed over to the alternative treatment for the second 14-day period. Blood and urine samples were collected at appropriate times for evaluation of digoxin and cilomilast steady-state pharmacokinetic parameters. The size of the study was sufficient to achieve 90% power to correctly exclude an effect of cilomilast.

RESULTS

Twelve of the 16 subjects enrolled completed the study. There were 4 withdrawals--1 due to noncompliance, 1 due to a positive drug screening, and 2 due to adverse events. At steady state, cilomilast 15 mg BID had no significant effect on the steady-state pharmacokinetic parameters of digoxin, with 90% CIs for both primary end points--area under the plasma concentration-time curve (AUC) over a 24-hour dosing interval and minimum plasma concentration--completely contained within the specified interval for equivalence (0.80-1.25). A mean reduction in maximum observed plasma concentration of digoxin of 11% was observed during coadministration with cilomilast, and time to maximum concentration was delayed by a median of 1 hour, suggesting a small reduction in the rate of digoxin absorption. Digoxin did not appear to markedly affect cilomilast steady-state pharmacokinetics. The most frequently reported adverse event was headache.

CONCLUSIONS

Cilomilast 15 mg BID had no clinically significant effect on steady-state AUC or on predose trough plasma concentrations of digoxin (375 microg once daily). The steady-state pharmacokinetics of cilomilast 15 mg BID were similar whether administered alone or with digoxin at steady state (375 microg once daily).

Differential pharmacokinetics of digoxin in elderly patients

Digoxin remains one of the most commonly prescribed of all cardiac medications. The main indications for digoxin usage include atrial fibrillation and heart failure; both these conditions are more prevalent in older patients. Given the aging population and the increasing incidence of heart failure we would expect prescribing of digoxin to remain as frequent or to even increase in older patients. Older patients are also more likely to develop toxicity and diagnosis of digoxin toxicity can be difficult in this group. Numerous components contribute to the development of toxicity in older patients, ranging from aging-related changes in renal function or body mass to polypharmacy and possible interactions with digoxin. It is therefore important to understand how the pharmacokinetics of digoxin may be altered in the older population. Application of basic pharmacological principles may be helpful in anticipating these problems. This review describes the pharmacokinetics of digoxin, the changes in pharmacokinetics with increasing age and how concomitant disease states or drug interactions may affect the pharmacokinetics of digoxin. Greater knowledge about the causes and prevention of digoxin toxicity should further reduce the morbidity and mortality arising from digoxin toxicity, especially in the elderly population.

Cardiovascular pharmacology of aging

Despite the relative paucity of drug trials in the old and especially the very old (> 85 years), some general principles of pharmacology in the aging patient can be taken from available data and clinical experience. The pharmacokinetic changes most consistently seen with aging occur in the volume of distribution, clearance, and half-life of a drug. Renal drug clearance is consistently diminished with aging. Hepatic metabolism is more variably affected, and in contrast to renal clearance, no reliable formula exists to estimate hepatic drug clearance. Pharmacodynamic changes, although present, are less well studied or described in the elderly. Drug interactions and adverse drug reactions increase with increasing numbers of medications prescribed and represent a complex interplay of age, underlying disease, and number and types of medications. The clinical caveats that apply to drug prescription in the very old include reduced starting doses with slow incremental increases; elimination of unnecessary medications; and anticipating and monitoring for drug interactions and ADRs, especially when prescribing warfarin, digoxin, and amiodarone. Future studies that look at the aging patient in the presence of effects of age, physiology, gender, comorbid illness, and multiple drug therapies may help evolve a new set of paradigms for geriatric drug prescribing.

Symposium on geriatrics--Part I: Drug prescribing for elderly patients

OBJECTIVE

To describe the pharmacokinetic and pharmacodynamic changes that occur with aging and to discuss common problems noted with the use of medications often prescribed for elderly patients.

DESIGN

We searched the medical literature, reviewed pertinent articles, and summarized drug-related information applicable to geriatric patients.

RESULTS

Use of medications is common in the elderly population; most elderly persons take two or more different medications each day. Aging is associated with anatomic and physiologic changes that can have an effect on how medications are handled. Such changes include alterations in various volumes of drug distribution and in drug absorption, metabolism, and clearance. Elderly patients may also have increased or decreased drug effects because of alteration in receptor response. These changes in pharmacokinetics and pharmacodynamics may result in a prolonged drug half-life, an increased potential for drug toxicity, and a greater likelihood for adverse drug reactions.

CONCLUSION

Medications for elderly patients should be prescribed only after the anatomic and physiologic changes of aging are understood and with increased surveillance for potential drug toxicity or adverse drug reactions.