Edema and principles of diuretic use

Diuretics: a review

Diuretics, in one form or another, have been around for centuries and this review sets out to chart their development and clinical use. Starting with the physiology of the kidney, it progresses to explain how diuretics actually work, via symports on the inside of the renal tubules. The different classes of diuretics are characterized, along with their mode of action. The clinical use of diuretics in conditions like congestive cardiac failure and hypertension, as well as some rarer, but clinically important, conditions is then examined. An account is given of the adverse effects of diuretics and how they come about. Common adverse effects like hypokalaemia and hyponatraemia are examined in some detail, and other electrolyte disturbances like hypomagnesaemia also gain a mention. Diuretic use in chronic kidney disease is examined and new guidelines that have been introduced are presented. A section on diuretic abuse is included as this is becoming an all too common clinical scenario, and the sometimes tragic consequences of this abuse are emphasized. Diuretics also find a role in the diagnosis of forms of renal tubular acidosis and this role is explored. Finally, a selection of some of the newer approaches to diuretic therapy are presented, often the consequence of the increasing development of molecular biology, and some of the novel compounds – which may be in drug formularies of the future – are revealed.

Anti-edematous effects of tolvaptan in experimental rodent models

PURPOSE

The aim of this study was to evaluate the therapeutic efficacy of tolvaptan, a vasopressin V(2) receptor antagonist, on edema in two rat models: 1) histamine-induced vascular hyperpermeability of the dorsal skin and 2) carrageenan-induced paw edema.

METHODS

In the skin vascular hyperpermeability model, 3 h after oral administration of tolvaptan or the natriuretic agent furosemide, rats were intravenously injected with Evans Blue (EB), followed by intradermal injection of 10 μg of histamine into the dorsal skin. One hour later, blood was collected to measure serum parameters. EB leakage area into the dorsal skin was also measured. Urine was collected for 4 h to determine urine parameters. In the paw edema model, edema was induced by injecting 1% w/v carrageenan into the right hind paw. Paw volume was measured hourly for 5 h. Tolvaptan or furosemide was orally administered 1 h before carrageenan injection.

RESULTS

A single oral dose of tolvaptan (1-10 mg/kg) elicited marked and dose-dependent aquaresis, and improvements in edema. Similar effects were observed with furosemide (30 mg/kg). Tolvaptan tended to elevate the serum sodium level while furosemide caused a significant decrease.

CONCLUSION

Tolvaptan had anti-edematous effects in two different rat models. By increasing free water excretion, tolvaptan may be more advantageous for certain patients than loop diuretics because it does not cause electrolyte loss, and may prevent electrolyte abnormities, such as hyponatremia. These results suggest that tolvaptan has potential clinical benefits for the treatment of edema.

Conivaptan: a dual vasopressin receptor v1a/v2 antagonist [corrected]

Several fluid retentive states such as heart failure, cirrhosis of the liver, and syndrome of inappropriate antidiuretic hormone secretion are associated with inappropriate elevation in plasma levels of arginine vasopressin (AVP), a neuropeptide that is secreted by the hypothalamus and plays a critical role in the regulation of serum osmolality and in circulatory homeostasis. The actions of AVP are mediated by three receptor subtypes V1a, V2, and V1b. The V1a receptor regulates vasodilation and cellular hypertrophy while the V2 receptor regulates free water excretion. The V1b receptor regulates adrenocorticotropin hormone release. Conivaptan is a nonpeptide dual V1a/V2 AVP receptor antagonist. It binds with high affinity, competitively, and reversibly to the V1a/V2 receptor subtypes; its antagonistic effect is concentration dependent. It inhibits CYP3A4 liver enzyme and elevates plasma levels of other drugs metabolized by this enzyme. It is approved only for short-term intravenous use. Infusion site reaction is the most common reason for discontinuation of the drug. In animals conivaptan increased urine volume and free water clearance. In heart failure models it improved hemodynamic parameters and free water excretion. Conivaptan has been shown to correct hyponatremia in euvolemic or hypervolemic patients. Its efficacy and safety for short-term use have led to the Food and Drug Administration (FDA) approval of its intravenous form for the correction of hyponatremia in euvolemic and hypervolemic states. Despite its ability to block the action of AVP on V1a receptors, no demonstrable benefit from this action was noted in patients with chronic compensated heart failure and it is not approved for this indication. Consideration should be given to further evaluation of its potential benefits in patients with acute decompensated heart failure.

Tolvaptan: a selective vasopressin type 2 receptor antagonist in congestive heart failure

The neurohormone arginine vasopressin plays a significant role in the regulation of volume homeostasis, which is mediated via vasopressin type 2 (V2) receptors in the collecting tubules of the kidney. Diseases that are accompanied by abnormal volume homeostasis, including congestive heart failure and cirrhosis, are a frequent cause of hospital admissions and increasing healthcare costs. Recently, several nonpeptide V2 receptor antagonists have emerged as promising agents in the management of these conditions with the advantage of having no electrolyte abnormalities, neurohormonal activation or worsening renal insufficiency. Tolvaptan, a highly selective nonpeptide V2 receptor antagonist, has demonstrated an improvement in the volume status, osmotic balance and haemodynamic profile in preclinical and Phase II trials in patients with congestive heart failure and is currently undergoing testing in Phase III trials. This review discusses the evidence for the potential uses of tolvaptan, and its pharmacology and pharmacokinetics, particularly in congestive heart failure.

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.

[Torasemide (LUPRAC): a review of its pharmacological and clinical profile]

Loop diuretics potently excrete water and electrolytes and therefore have been widely prescribed for the treatment of various kinds of edema for a long time. The potent diuretic action of loop diuretics, however, often causes hypokalemia, and therefore potassium sparing diuretics have also been supplied as a concomitant drug. Torasemide (LUPRAC), a novel diuretics, shows not only an effective loop diuretic action but also a potassium sparing action due to its anti-aldosteronergic effect. Torasemide also has a high bioavailability and is only slightly influenced by meals in humans. In addition, its pharmacodynamic features contribute to its stable diuretic action without any individual differences. In animal experiments, torasemide showed about a tenfold more potent diuretic action in comparison with furosemide, an authentic loop diuretic. On the one hand, the increase in the urinary potassium excretion by torasemide was relatively slight compared to the increase in urinary sodium excretion and, as a result, the urinary sodium to potassium (Na+/K+) ratio increased. The diuretic profile of torasemide was equal to that of the concomitant use of furosemide and an anti-aldosteronergic drug, spironolactone. Torasemide showed a significant efficacy and safety in comparison with furosemide in the patients with edema in both domestic and foreign clinical studies. Moreover, torasemide also showed a decreased rate of cardiac death in comparison to furosemide in patients with chronic heart failure in a large-scale clinical study (TORIC Study). The difference in cardiac death between these two diuretics has been suggested to depend on the anti-aldosteronergic effect of torasemide. In Japan, no new loop diuretics have been developed in over 10 years. Torasemide is therefore expected to be useful as an effective diuretic for diseases with edema.

Safety of drugs commonly used to treat hypertension, dyslipidemia, and type 2 diabetes (the metabolic syndrome): part 1

The benefits of blood pressure lowering, lipid lowering, and glycemic control on morbidity and mortality have been established in major long-term clinical trials. The most extensive information is available for diuretics or beta-blockers in hypertension, hepatic hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) in dyslipidemia, and insulin or sulfonylureas in diabetes. Other drug classes provide similar improvements in blood pressure, lipid profile, and glycemic control, and thereby might be expected to provide comparable long-term benefits. As a result, national guidelines advocate treating patients aggressively in order to achieve control of blood pressure low-density lipoprotein (LDL) cholesterol, and blood glucose. The risks associated with drug treatment are generally class-specific. Among antidiabetic agents, sulfonylureas and insulin are associated with risk for severe hypoglycemia, metformin with risk for lactic acidosis, and troglitazone with risk for idiosyncratic hepatocellular injury. Similarly, widely used antihypertensive and lipid-lowering agents are associated with risk for serious complications, such as angioedema with angiotensin-converting enzyme inhibitors, possible increased risk for myocardial infarction and cancer with calcium antagonists, and myositis and liver dysfunction with statins. Physicians must take an aggressive approach to patient management in order to achieve a level of disease control that optimally reduces risk for morbidity and mortality. Serious adverse events may occur rarely with most drug classes; these events can be minimized by appropriately monitoring or selecting patients for treatment.