Role of duration of diuretic effect in preventing sodium retention

Pharmacotherapeutic principles of fluid management in heart failure

Introduction: Heart failure is a major public health concern that is expected to increase over the decades to come. Despite significant advances, fluid overload and congestion remain a major therapeutic challenge. Vascular congestion and neurohormonal activation are intricately linked and the goal of therapy fundamentally aims to reduce both.Areas covered: The authors briefly review a number of core concepts that elucidate the link between fluid overload and neuro-hormonal activation. This is followed by a review of heart-kidney interactions and the impact of diuresis in this setting. Following an in-depth review of currently available pharmacological agents, the rationale and evidence behind their use, the authors end with a brief note on novel agents/approaches to aid volume management in HF.Expert opinion: A number of non-pharmacological advances in the management of volume overload in heart failure, though promising - are associated with a number of shortcomings. Pharmacological therapy remains the cornerstone of volume management. A number of novel approaches, utilizing existing therapies as well as the emergence of new agents over the past decade bode well for the vulnerable HF population.

Diuretic Resistance in Heart Failure

Purpose of review:

Diuretic resistance (DR) occurs along a spectrum of relative severity and contributes to worsening of acute heart failure (AHF) during an inpatient stay. This review gives an overview of mechanisms of DR with a focus on loop diuretics and summarizes the current literature regarding the prognostic value of diuretic efficiency and predictors of natriuretic response in AHF.

Recent findings:

The pharmacokinetics of diuretics are impaired in chronic heart failure, but little is known about mechanisms of DR in AHF. Almost all diuresis after administration of a loop diuretic dose occurs in the first few hours after administration and within-dose DR can develop. Recent studies suggest that DR at the level of the nephron may be more important than defects in diuretic delivery to the tubule. Because loop diuretics induce natriuresis, urine sodium (UNa) concentration may serve as a functional, physiologic and direct measure for diuretic responsiveness to a given loop diuretic dose.

Summary:

Identifying and targeting individuals with DR for more aggressive, tailored therapy represents an important opportunity to improve outcomes. A better understanding of the mechanistic underpinnings of DR in AHF is needed to identify additional biomarkers and guide future trials and therapies.

Sodium and Fluid Excretion With Torsemide in Healthy Subjects is Limited by the Short Duration of Diuretic Action

BACKGROUND

Loop diuretics are highly natriuretic but their short duration of action permits postdiuretic sodium retention, which limits salt loss unless dietary salt is severely restricted. We tested the hypothesis that a more prolonged duration of action would enhance salt loss.

METHODS AND RESULTS

Ten healthy participants were crossed over between 20 mg of oral immediate-release or extended-release (ER) torsemide while consuming a fixed diet with 300 mmol·d^-1 of Na⁺. Compared with immediate-release, plasma torsemide after ER was 59% lower at 1 to 3 hours but 97% higher at 8 to 10 hours as a result of a >3-fold prolongation of time to maximal plasma concentrations. The relationship of natriuresis to log torsemide excretion showed marked hysteresis, but participants spent twice as long with effective concentrations of torsemide after ER, thereby enhancing diuretic efficiency. Compared with immediate-release, ER torsemide did not reduce creatinine clearance and increased fluid (1634±385 versus 728±445 mL, P<0.02) and Na⁺ output (98±15 versus 42±17 mmol, P<0.05) despite an 18% reduction in exposure. Neither formulation increased K⁺ excretion.

CONCLUSIONS

Torsemide ER prolongs urine drug levels, thereby increasing the time spent with effective drug concentrations, reduces postdiuretic Na⁺ retention, and moderates a fall in glomerular filtration rate. It caused significant Na⁺ loss even during very high salt intake. Thus, a short duration of action limits salt loss with loop diuretics. These conclusions warrant testing in subjects with edema and heart failure.

A perspective on diuretic resistance in chronic congestive heart failure

Chronic congestive heart failure (CHF) is a complex disorder characterized by inability of the heart to keep up the demands on it, followed by the progressive pump failure and fluid accumulation. Although the loop diuretics are widely used in heart failure (HF) patients, both pharmacodynamic and pharmacokinetic alterations are thought to be responsible for diuretic resistance in these patients. Strategies to overcome diuretic resistance include sodium intake restriction, changes in diuretic dose and route of administration and sequential nephron diuretic therapy. In this review, we discuss the definition, prevalence, mechanism of development and management strategies of diuretic resistance in HF patients.

Treating Diuretic Resistance: An Overview

Loop diuretics are central to the management of fluid overload in acute decompensated heart failure. However, a variance in the response to loop diuretics can alter a patient's clinical course and has an adverse effect on clinical outcomes. Thus, a diminished response to loop diuretics is an important clinical issue. Factors thought to contribute to diuretic resistance include erratic oral absorption in congested states and postdiuretic sodium retention. Further contributing to diuretic resistance in patients with advanced heart failure are decreases in renal perfusion and alterations in sodium handling that occur in an attempt to maintain circulatory homeostasis. Several pharmacologic interventions have been used to improve diuretic response. Intravenous diuretic administration, increasing diuretic doses, or changing diuretic agents can potentially overcome pharmacokinetic obstacles which contribute to drug resistance. Combination diuretic therapy may be useful to overcome increased sodium retention, dopamine may improve renal perfusion, and hypertonic saline may transiently increase intravascular volume and improve sodium delivery to the tubules of the nephron. Despite the prevalence of diuretic resistance, there remains a paucity of clinical trial evidence to help guide therapy in these patients.

Randomized, open-label, blinded-endpoint, crossover, single-dose study to compare the pharmacodynamics of torasemide-PR 10 mg, torasemide-IR 10 mg, and furosemide-IR 40 mg, in patients with chronic heart failure

Purpose

Diuretics are the primary treatment for the management of chronic heart failure (HF) symptoms and for the improvement of acute HF symptoms. The rate of delivery to the site of action has been suggested to affect diuretic pharmacodynamics. The main objective of this clinical trial was to explore whether a prolonged release tablet formulation of torasemide (torasemide-PR) was more natriuretically efficient in patients with chronic HF compared to immediate-release furosemide (furosemide-IR) after a single-dose administration. Moreover, the pharmacokinetics of torasemide-PR, furosemide-IR, and torasemide-IR were assessed in chronic HF patients as well as urine pharmacodynamics.

Methods

Randomized, open-label, blinded-endpoint, crossover, and single-dose Phase I clinical trial with three experimental periods. Torasemide-PR and furosemide-IR were administered as a single dose in a crossover fashion for the first two periods, and torasemide-IR 10 mg was administered for the third period. Blood and urine samples were collected at fixed timepoints. The primary endpoint was the natriuretic efficiency after administration of torasemide-PR and furosemide-IR, defined as the ratio between the average drug-induced natriuresis and the average drug recovered in urine over 24 hours.

Results

Ten patients were included and nine completed the study. Here, we present the results from nine patients. Torasemide-PR was more natriuretically efficient than furosemide-IR (0.096±0.03 mmol/μg vs 0.015±0.0007 mmol/μg; P<0.0001). Mictional urgency was lower and more delayed with torasemide-PR than with furosemide-IR.

Conclusion

In a study with a limited sample size, our results suggest that 10 mg of torasemide-PR is more natriuretically efficient than 40 mg of furosemide-IR after single-dose administration in patients with chronic HF over a 24-hour collection period. Further studies are necessary to evaluate potential pharmacodynamic differences between torasemide formulations and to assess its impact on clinical therapeutics.

Update in diuretic therapy: clinical pharmacology

All diuretics except spironolactone exert their effects from the lumen of the nephron. Thus, to exert an effect, they must reach the urine. Pharmacokinetics (PK) describes this access. Different edematous disorders can affect access to this site of action and therein affect response to a diuretic. In addition, once a diuretic reaches the site of action, a response ensues. The characteristics of this response that can be affected by a patient's clinical condition are described by the pharmacodynamics (PD) of a diuretic. To understand the mechanisms of abnormal response to a diuretic one must dissect its PK and PD in different edematous disorders. For example, in patients with renal insufficiency, the mechanism of poor diuretic response is PK. In contrast, in patients with cirrhosis or in those with congestive heart failure, it is PD. In patients with nephrotic syndrome, both PK and PD are operative. These different mechanisms mandate differences in therapeutic strategy, as explained in this article.

A pilot study comparing furosemide and hydrochlorothiazide in patients with hypertension and stage 4 or 5 chronic kidney disease

Furosemide is the diuretic of choice for the treatment of hypertension in chronic kidney disease but the adaptative changes in the distal nephron may decrease its efficacy. Hydrochlorothiazide is not believed to be efficient in this setting. In a randomized, double-blind, cross-over trial, 23 patients with hypertension and stage 4 or 5 chronic kidney disease received long-acting furosemide (60 mg) and hydrochlorothiazide (25 mg) for 3 months and then both diuretics for 3 months. Sodium and chloride fractional excretions were measured after 3 months of each diuretic and then after their association. A trend towards an increase in the fractional excretion of sodium and chloride was observed with furosemide and hydrochlorothiazide (P=not significant). The association of the two diuretics increased the fractional excretions of sodium and chloride from 3.4±1.8 to 4.9±2.8 and from 3.8±2.0 to 6.0±3.1, respectively (P<.05). Furosemide and hydrochlorothiazide decreased mean blood pressure by the same extent. The association of the two diuretics was more efficient on blood pressure. There were no differences between furosemide and hydrochlorothiazide with respect to natriuresis and blood pressure control in patients with hypertension and chronic kidney disease.

Diuretics in clinical practice. Part I: mechanisms of action, pharmacological effects and clinical indications of diuretic compounds

IMPORTANCE OF THE FIELD

Diuretics are among the most important drugs of our therapeutic armamentarium and have been broadly used for > 50 years, providing important help towards the treatment of several diseases. Although all diuretics act primarily by impairing sodium reabsorption in the renal tubules, they differ in their mechanism and site of action and, therefore, in their specific pharmacological properties and clinical indications. Loop diuretics are mainly used for oedematous disorders (i.e., cardiac failure, nephrotic syndrome) and for blood pressure and volume control in renal disease; thiazides and related agents are among the most prescribed drugs for hypertension treatment; aldosterone-blockers are traditionally used for primary or secondary aldosteronism; and other diuretic classes have more specific indications.

AREAS COVERED IN THIS REVIEW

This article discusses the mechanisms of action, pharmacological effects and clinical indications of the various diuretic classes used in everyday clinical practice, with emphasis on recent knowledge suggesting beneficial effects of certain diuretics on clinical conditions distinct from the traditional indications of these drugs (i.e., heart protection for aldosterone blockers).

WHAT THE READER WILL GAIN

Reader will gain insights into the effective use of diuretic agents for various medical conditions, representing their established or emerging therapeutic indications.

TAKE HOME MESSAGE

Knowledge of the pharmacologic properties and mechanisms of action of diuretic agents is a prerequisite for the successful choice and effective clinical use of these compounds.

Challenges in advanced chronic heart failure: drug therapy

Despite advances in both drug and device treatment of chronic heart failure (CHF) over the last 20 years, many patients still progress to a stage of advanced CHF, characterized by increasing symptoms and declining functional status. Future drug management of such patients presents many challenges. This review focuses on the issue of optimizing standard medical therapy in advanced CHF, the treatment of diuretic resistance and hyponatremia. As well as prescribing drugs in this phase of the disease, the system of care used to deliver therapy is crucial. On its own, multiprofessional heart failure care can improve outcomes for these patients. Finally, this review also addresses the drugs and model of care used to deliver palliative care in the end stage of advanced CHF.

Comparison of repeated-dose pharmacokinetics of prolonged-release and immediate-release torasemide formulations in healthy young volunteers

The major aim of the study was to compare the pharmacokinetic profile of repeated-dose administration of a prolonged-release (PR) formulation of torasemide with that of an immediate-release (IR) dosage. Sixteen volunteers received one daily dose, on four consecutive days, of 10 mg of torasemide-PR or torasemide-IR in a single-blind, two-treatment, two-period, repeated-dose, cross-over, sequence-randomized clinical trial. Blood samples were collected at various time points on day 1 (single-dose) and on day 4 (repeated-dose) and torasemide concentrations were analysed by LC/MS/MS. Diuretic effect and urine electrolytes were measured. Urinary urgency was subjectively assessed by visual analogue scales. Safety and tolerability were also determined. Based on logged values, bioequivalence parameters, were: on day 1, ratio = 1.07 (90% CI 1.02-1.1), C(max) ratio = 0.69 (90% CI 0.67-0.73); and on day 4, ratio = 1.02 (90% CI 0.98-1.05), C(max) ratio = 0.62 (90% CI 0.55-0.70). PR had longer t(max) than IR and showed significantly lower fluctuations of plasma concentrations. Urine evaluations were similar with both formulations, although PR showed a lower urine volume in the first hours post-administration. Episodes of acute urinary urgency occurred later and were subjectively less intensive with PR. No significant adverse events were reported.

Continuous infusion versus bolus injection of loop diuretics in congestive heart failure

BACKGROUND

Loop diuretics, when given as intermittent bolus injections in acutely decompensated heart failure, may cause fluctuations in intravascular volume, increased toxicity and development of tolerance. Continuous infusion has been proposed to avoid these complications and result in greater diuresis, hopefully leading to faster symptom resolution, decrease in morbidity and possibly, mortality.

OBJECTIVES

To compare the effects and adverse effects of continuous intravenous infusion of loop diuretics with those of bolus intravenous administration among patients with congestive heart failure Class III-IV.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 2, 2003), MEDLINE (1966 to 2003), EMBASE (1980 to 2003) and the HERDIN database. We also contacted pharmaceutical companies .

SELECTION CRITERIA

Randomized controlled trials comparing the efficacy of continuous intravenous infusion versus bolus intravenous administration of loop diuretics in congestive heart failure were included

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed study eligibility, methodological quality and did data extraction. Included studies were assessed for validity. Authors were contacted when feasible. Adverse effects information was collected from the trials.

MAIN RESULTS

Eight trials involving 254 patients were included. In seven studies which reported on urine output, the output (as measured in cc/24 hours) was noted to be greater in patients given continuous infusion with a weighted mean difference (WMD) of 271 cc/24 hour (95%CI 93.1 to 449; p<0.01). Electrolyte disturbances (hypokalemia, hypomagnesemia) were not significantly different in the two treatment groups with a relative risk (RR) of 1.47 (95%CI 0.52 to 4.15; p=0.5). Less adverse effects (tinnitus and hearing loss) were noted when continuous infusion was given, RR 0.06 (95%CI 0.01 to 0.44; p=0.005). Based on a single study, the duration of hospital stay was significantly shortened by 3.1days with continuous infusion WMD -3.1 (95%CI -4.06 to -2.20; p<0.0001) while cardiac mortality was significantly different in the two treatment groups, RR 0.47 (95% CI 0.33 to 0.69; p<0.0001). Based on two studies, all cause mortality was significantly different in the two treatment groups, RR 0.52 (95%CI 0.38 to 0.71; p<0.0001).

AUTHORS' CONCLUSIONS

Currently available data are insufficient to confidently assess the merits of the two methods of giving intravenous diuretics. Based on small and relatively heterogenous studies, this review showed greater diuresis and a better safety profile when loop diuretics were given as continuous infusion. The existing data still does not allow definitive recommendations for clinical practice and larger studies should be done to more adequately settle this issue.

Drug dosing in chronic kidney disease

Patients with chronic kidney disease (CKD) are at high risk for adverse drug reactions and drug-drug interactions. Drug dosing in these patients often proves to be a difficult task. Renal dysfunction-induced changes in human pathophysiology regularly results may alter medication pharmacodynamics and handling. Several pharmacokinetic parameters are adversely affected by CKD, secondary to a reduced oral absorption and glomerular filtration; altered tubular secretion; and reabsorption and changes in intestinal, hepatic, and renal metabolism. In general, drug dosing can be accomplished by multiple methods; however, the most common recommendations are often to reduce the dose or expand the dosing interval, or use both methods simultaneously. Some medications need to be avoided all together in CKD either because of lack of efficacy or increased risk of toxicity. Nevertheless, specific recommendations are available for dosing of certain medications and are an important resource, because most are based on clinical or pharmacokinetic trials.

[Modern differential therapy with diuretics]

Diuretics block different electrolyte transporters in renal tubular cells. Their predominant action is inhibition of renal sodium chloride reabsorption, however, and achievement of a negative body sodium balance is the principal goal of diuretic therapy in patients with hypertension and edema. Several classes of diuretics can be distinguished with respect to the sites of sodium reabsorption along the nephron, but loop diuretics and distal-tubular diuretics (incl. thiazides) are the most widely used. The latter have a less potent natriuretic effect than loop diuretics, but their long duration of action predispose them for treatment of patients with uncomplicated hypertension. In conditions of gross edema, e.g. heart and/or renal failure, distal-tubular diuretics lose their efficacy and must be replaced by or combined with loop diuretics ("sequential nephron blockade"). Aldosterone antagonists are unique among diuretics because they improve survival in patients with heart failure independently of their effect on sodium metabolism.

Continuous infusion versus bolus injection of loop diuretics in congestive heart failure

BACKGROUND

Loop diuretics, when given as intermittent bolus injections in acutely decompensated heart failure, may cause fluctuations in intravascular volume, increased toxicity and development of tolerance. Continuous infusion has been proposed to avoid these complications and result in greater diuresis, hopefully leading to faster symptom resolution, decrease in morbidity and possibly, mortality.

OBJECTIVES

To compare the effects and adverse effects of continuous intravenous infusion of loop diuretics with those of bolus intravenous administration among patients with congestive heart failure Class III-IV.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 2, 2003), MEDLINE (1966 to 2003), EMBASE (1980 to 2003) and the HERDIN database. We also contacted pharmaceutical companies.

SELECTION CRITERIA

Randomized controlled trials comparing the efficacy of continuous intravenous infusion versus bolus intravenous administration of loop diuretics in congestive heart failure were included

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed study eligibility, methodological quality and did data extraction. Included studies were assessed for validity. Authors were contacted when feasible. Adverse effects information was collected from the trials.

MAIN RESULTS

Eight trials involving 254 patients were included. In seven studies which reported on urine output, the output (as measured in cc/24 hours) was noted to be greater in patients given continuous infusion with a weighted mean difference (WMD) of 271 cc/24 hour (95%CI 93.1 to 449; p<0.01). Electrolyte disturbances (hypokalemia, hypomagnesemia) were not significantly different in the two treatment groups with a relative risk (RR) of 1.47 (95%CI 0.52 to 4.15; p=0.5). Less adverse effects (tinnitus and hearing loss) were noted when continuous infusion was given, RR 0.06 (95%CI 0.01 to 0.44; p=0.005). Based on a single study, the duration of hospital stay was significantly shortened by 3.1days with continuous infusion WMD -3.1 (95%CI -4.06 to -2.20; p<0.0001) while cardiac mortality was not significantly different in the two treatment groups, RR 0.47 (95% CI 0.33 to 0.69; p<0.0001). Based on two studies, all cause mortality was not significantly different in the two treatment groups, RR 0.52 (95%CI 0.38 to 0.71; p<0.0001).

REVIEWER'S CONCLUSIONS

Currently available data are insufficient to confidently assess the merits of the two methods of giving intravenous diuretics. Based on small and relatively heterogenous studies, this review showed greater diuresis and a better safety profile when loop diuretics were given as continuous infusion. The existing data still does not allow definitive recommendations for clinical practice and larger studies should be done to more adequately settle this issue.

A study of the pharmacodynamic differences between immediate and extended release bumetanide formulations

Optimized bumetanide extended (ER) and immediate release (IR) formulations were developed using fluid bed layering and coating techniques. We postulated that the ER bumetanide formulation would have more effective and sustained diuretic and saluretic effects than IR. The diuretic/saluretic effects of both formulations were measured in rabbits (n=8) for two days after dosing with 1mg/kg bumetanide. During the first day, both formulations produced 2-3 times more urine volume and sodium excretion than baseline. In the first 24h, despite less bumetanide excretion from the ER formulation (101+/-13.9microg/kg compared to 146+/-14.6microg/kg for the IR formulation; P<0.04); the ER formulation produced diuresis and natriuresis that was equivalent to that of the IR formulation. In contrast, urine production in the IR formulation group fell below that of placebo controls on day 2. During the second day, the ER formulation was noted to produce persistent bumetanide excretion; the diuretic and natriuretic effects were not statistically significant from baseline control. We speculate that the decrease in response to bumetanide observed especially for the IR formulation during the second day may be due to the activation of compensatory counter-regulatory homeostatic mechanism(s). We conclude that the ER formulation had similar diuretic/saluretic effects but better drug excretion to urine production efficiencies than the IR formulation in the healthy rabbit model. The ER formulation, while providing comparable diuretic/saluretic effect to the IR formulation, offers the advantage of avoiding the initial, rapid and robust diuretic effect experienced with the IR formulations. Taken together, the data provide sufficient basis to warrant further investigation and refinement of our ER bumetanide formulation in humans.

Mechanisms and management of diuretic resistance in congestive heart failure

Diuretic drugs are used almost universally in patients with congestive heart failure, most frequently the potent loop diuretics. Despite their unproven effect on survival, their indisputable efficacy in relieving congestive symptoms makes them first line therapy for most patients. In the treatment of more advanced stages of heart failure diuretics may fail to control salt and water retention despite the use of appropriate doses. Diuretic resistance may be caused by decreased renal function and reduced and delayed peak concentrations of loop diuretics in the tubular fluid, but it can also be observed in the absence of these pharmacokinetic abnormalities. When the effect of a short acting diuretic has worn off, postdiuretic salt retention will occur during the rest of the day. Chronic treatment with a loop diuretic results in compensatory hypertrophy of epithelial cells downstream from the thick ascending limb and consequently its diuretic effect will be blunted. Strategies to overcome diuretic resistance include restriction of sodium intake, changes in dose, changes in timing, and combination diuretic therapy.

The rational use of diuretics in heart failure

Congestive heart failure is a progressive hemodynamic disorder associated with significant morbidity and mortality. Concomitant renal dysfunction is frequently seen in patients with heart failure, and can compromise fluid regulation, leading to acute decompensation, and increased morbidity and mortality. Diuretic therapy has been the mainstay for treatment of congestive symptoms, despite documented mortality benefits. Misuse or overuse of diuretics can have negative consequences in heart failure, and optimizing diuretic efficiency may improve outcomes. In addition, new agents targeting elevated neuropeptides may prove to be beneficial in regulating fluid status and optimizing renal function.

Association between adherence to diuretic therapy and health care utilization in patients with heart failure

STUDY OBJECTIVE

To determine the relationship between adherence to diuretic therapy and health care utilization.

DESIGN

Prospective, observational study.

SETTING

University-affiliated medical center.

PATIENTS

Forty-two patients with heart failure.

INTERVENTION

Electronic monitoring of adherence to diuretic therapy (percentage of diuretic prescription container openings) and to scheduling (percentage of container openings within a specific time).

MEASUREMENTS AND MAIN RESULTS

All patients were prescribed a diuretic, most commonly furosemide (88%). Patients varied widely in adherence to therapy (mu = 72% +/- 30%) and to scheduling (mu = 43% +/- 30%). Education was a predictor of drug-taking adherence (p=0.0062) but not of scheduling adherence. Log-linear models revealed that poor scheduling adherence was associated with increased cardiovascular-related hospitalizations (chi2 11.63, p=0.0006) and predicted more heart failure-related hospitalizations (chi2 4.04, p=0.0444). In contrast, neither measure was significantly associated with cardiovascular- or heart failure-related emergency department visits. We found a moderate correlation between scheduling adherence and taking adherence (r = 0.6513).

CONCLUSION

Patients taking a greater proportion of diuretic agents on schedule may decrease the risk of cardiovascular- and heart failure-related hospitalizations. If these findings are confirmed by a larger study, interventions to improve adherence and patient health outcomes should consider the timing of doses as well as the number of daily doses of a diuretic.

Loop diuretics: from the Na-K-2Cl transporter to clinical use

The diuretic response to loop diuretics in various disease states has consistently been found to be subnormal. One of the key determinants of the degree of diuretic response is the functional integrity of the sodium-potassium-chloride transporter in the loop of Henle. Studies in animal models suggest that expression/activity of the transporter may be affected by factors such as altered natural splicing events of NKCC2 (the gene encoding for the renal transporter), renal prostanoids, vasopressin, and other autacoids. We have reviewed the pharmacokinetics and pharmacodynamics of loop diuretics in health and in edematous disorders for which they are used. On the basis of evidence reviewed in this paper, we propose that altered expression or activity of the sodium-potassium-chloride transporter in the loop of Henle, in conjunction with events occurring in other segments of the nephron, possibly accounts for the altered diuretic response to these agents. Thus the modulators of this altered expression/activity could serve as important therapeutic targets for alternative diuretic regimens in these conditions.

Pharmacotherapy in congestive heart failure: diuretic resistance and strategies to overcome resistance in patients with congestive heart failure

Congestive heart failure is a complex clinical hemodynamic disorder characterized by chronic and progressive pump failure and fluid accumulation. Although the overall impact of diuretic therapy on congestive heart failure mortality remains unknown, diuretics remain a vital component of symptomatic congestive heart failure management. Over time, sodium and water excretion are equalized before adequate fluid elimination occurs. This phenomenon is thought to occur in one out of three patients with congestive heart failure on diuretic therapy and is termed diuretic resistance. In congestive heart failure, both pharmacokinetic and pharmacodynamic alterations are thought to be responsible for diuretic resistance. Due to disease chronicity, symptomatic management is vital to improved quality of life and enhancing diuretic response is therefore pivotal.

The clinical, cardiac, renal, arterial and neurohormonal effects of omapatrilat, a vasopeptidase inhibitor, in patients with chronic heart failure

OBJECTIVES

We sought to examine the effects of long-term vasopeptidase inhibition in patients with heart failure.

BACKGROUND

The long-term effects of omapatrilat, an agent that inhibits both neutral endopeptidase and angiotensin-converting enzyme, on clinical status, neurohormonal indexes and left ventricular function in patients with chronic heart failure (CHF) have not been previously documented.

METHODS

Forty-eight patients in New York Heart Association functional class II or III, with left ventricular ejection fraction (LVEF)< or =40% and in sinus rhythm were randomized to a dose-ranging pilot study of omapatrilat for 12 weeks. Measurements were performed at baseline and 12 weeks.

RESULTS

There was an improvement in functional status, as reported by the patient (p<0.001) and physician (p<0.001) at 12 weeks. Dose-dependent improvements in LVEF (p<0.001) and LV end-systolic wall stress (sigma) (p<0.05) were seen, together with a reduction in systolic blood pressure (p<0.05). There was evidence of a natriuretic effect (p<0.001), and total blood volume decreased (p<0.05). Omapatrilat induced an increase in postdose plasma atrial natriuretic peptide levels (p<0.01) in the high dose groups, with a reduction in predose plasma brain natriuretic peptide (p<0.001) and epinephrine (p<0.01) levels after 12 weeks of therapy. Omapatrilat was well tolerated.

CONCLUSIONS

The sustained hemodynamic, neurohumoral and renal effects of omapatrilat, together with improved functional status, suggest that vasopeptidase inhibition has potential as a new therapeutic modality for the treatment of CHF.

The influence of frusemide formulation on diuretic effect and efficiency

AIMS

Changes in drug delivery rate may result in clinically important changes in drug effects. For the loop diuretic frusemide, it would be desirable to develop controlled release preparations, that could maintain an effective urinary excretion rate over a prolonged period of time. The aim of this study was to investigate the influence of frusemide formulation on frusemide recovery, diuretic effect and efficiency.

METHODS

Twelve subjects were given 60 mg of four different frusemide controlled release formulations in a single-dose, double-blind, randomized 4-way cross-over design. The formulations were three study drugs with different extended dissolution rates (ER1Tab, ER2Tab and ER3Caps ) and one reference drug (LR). Urinary volume and contents of frusemide in urine were measured in samples collected over 24 h.

RESULTS

Substantial differences in frusemide recovery and diuretic efficiency were observed between LR and all other formulations. At 24 h, mean total frusemide recoveries of ER1Tab, ER2Tab and ER3Caps were 52%, 36% and 57% lower, respectively, compared with LR (P<0.01). Also at 24 h, mean total diuretic efficiency for ER1Tab, ER2Tab and ER3Caps was 83%, 31% and 135% higher, respectively, compared to LR. The rapid dissolution and absorption of LR resulted in a high diuretic response from 0 to 3 h after dosing. However, from 0 to 24 h, there were no differences in diuretic response between the formulations.

CONCLUSIONS

Controlled release formulations of frusemide with a low and extended rate of dissolution lead to a more prolonged absorption and subsequent diuresis, but still maintain a similar cumulative response, due to their higher diuretic efficiency.

The influence of drug input rate on the development of tolerance to frusemide

AIMS

Understanding the impact of drug input rate on its pharmacokinetic-pharmacodynamic relationship may lead to a more optimal drug therapy. The aim of the present study was to investigate the influence of the rate of administration on tolerance development to frusemide, by giving the drug at four different infusion rates.

METHODS

Eight healthy volunteers were given 10 mg of frusemide on four different occasions, as a constant-rate intravenous infusion during 10, 30, 100 and 300 min, respectively. Urinary volume and contents of frusemide and sodium were measured in samples collected over 8 h.

RESULTS

The four different infusion rates systematically influenced the frusemide excretion rate versus diuretic and natriuretic response relationship. Counter-clockwise hysteresis occurred for the most rapid infusion rate, whereas a progressive clockwise hysteresis was observed for the slower infusions, indicating development of tolerance. For each subject, diuresis and natriuresis were modeled for all four treatments simultaneously, using a feedback tolerance model. It was not possible to describe the data using a model without tolerance. The time course of tolerance development showed remarkable differences between the infusion rates. The intensity of maximum tolerance development was significantly less for the slowest infusion rate compared with the more rapid infusions and it appeared significantly later. However, no differences in diuretic or natriuretic response were found between the treatments.

CONCLUSIONS

The direction of the hysteresis loop is dependent on the input rate of frusemide. After the administration of a single low dose of frusemide, the time course of tolerance, rather than the integrated time course of tolerance, is influenced by the drug input rate.

Pharmacodynamics of variable patient compliance: implications for pharmaceutical value

Pharmaceutical value, a multidimensional factor that includes proven efficacy, is now crucial to market success. A key parameter of value is reliability in use, determined by the several sources of variance in drug response, e.g. the Harter-Peck model, based on linear pharmacometrics of theophylline, whose dose-response has an estimated 80% coefficient of variation, due mainly to variable pharmacokinetics and non-compliance. The main forms of non-compliance are multiday intervals between doses, the impact of which is difficult to assess because too little is known of the time-course of drug actions after dosing stops ('off-responses'). Omeprazole, the best-selling drug, is an exception, and its off-response data reveal markedly non-linear pharmacodynamics that appear to filter most of the variance that a linear model passes, projecting a big gain in reliability. The impact of variable compliance is attenuated by 'forgiveness', the post-dose duration of effective action (4-5 days for omeprazole) minus its recommended dosing interval.

Combination diuretic therapy in severe congestive heart failure

Severe congestive heart failure (CHF) is often characterised by fluid retention. A (chronic) state of overhydration has a negative influence on both the quality of life and prognosis of these patients. Therefore, the use of diuretics remains a cornerstone in the treatment of heart failure. However, diuretic resistance, a failure to correct the hydration state adequately with the use of conventional dosages of loop diuretics, is a frequently occurring complication in the treatment of advanced stages of CHF. Several intra- and extrarenal mechanisms may be involved in the development of diuretic resistance. An important pathophysiological mechanism leading to diuretic resistance seen after chronic use of loop diuretics is the functional adaptation of the distal tubule. Studies in animals demonstrate that the sodium reabsorption capacity of this nephron segment increases significantly when the sodium delivery to this segment is augmented, as is the case during administration of loop diuretics. The use of combinations of diuretics acting on different segments of the nephron appears to be an effective option in the treatment of diuretic resistance. Several combinations have been used; however, the combination of a loop diuretic and a thiazide drug acting on the distal tubule appears to be the most effective. However, since the use of this combination may lead to serious adverse effects such as hypokalaemia, metabolic alkalosis and dehydration, careful monitoring of the patient of combination diuretic therapy is necessary.