Coadministration of thiazides increases the efficacy of loop diuretics even in patients with advanced renal failure

Role of the kidneys in resistant hypertension

Resistant hypertension is a failure to achieve goal BP (<140/90 mm Hg for the overall population and <130/80 mm Hg for those with diabetes mellitus or chronic kidney disease) in a patient who adheres to maximum tolerated doses of 3 antihypertensive drugs including a diuretic. The kidneys play a critical role in long-term regulation of blood pressure. Blunted pressure natriuresis, with resultant increase in extracellular fluid volume, is an important cause of resistant hypertension. Activation of the renin-angiotensin-aldosterone system, increased renal sympathetic nervous system activity and increased sodium reabsorption are important renal mechanisms. Successful treatment requires identification and reversal of lifestyle factors or drugs contributing to treatment resistance, diagnosis and appropriate treatment of secondary causes of hypertension, use of effective multidrug regimens and optimization of diuretic therapy. Since inappropriate renal salt retention underlies most cases of drug-resistant hypertension, the therapeutic focus should be on improving salt depleting therapy by assessing and, if necessary, reducing dietary salt intake, optimizing diuretic therapy, and adding a mineralocorticoid antagonist if there are no contraindications.

[Physiopathology and treatment of nephrotic syndrome complications]

The nephrotic syndrome is defined by a urinary protein excretion exceeding 3g per day, associated with hypoalbuminaemia (< 30 g/L) and hypoprotidaemia (< 60 g/L). The clinical consequences of the nephrotic syndrome are multiple, essentially dominated by sodium retention and oedema formation. The oedema physiopathology is related to both increased capillary permeability and primary activation of the Na/K pump in the collect duct. Other complications of the nephrotic syndrome include thromboembolic complications, dyslipidaemia, and infections. The treatment of these complications represents an important part of the general management of the nephritic syndrome.

Management of loop diuretic resistance in the intensive care unit

PURPOSE

The management of loop diuretic resistance in the intensive care unit (ICU) is reviewed.

SUMMARY

Volume overload, a common complication of fluid resuscitation, is frequently encountered in the ICU and is associated with numerous adverse effects, including pulmonary and peripheral edema, acute lung injury, and pleural effusions. Loop diuretics are used to treat volume overload and acute renal failure and to ameliorate their associated complications. When administered intravenously, these drugs induce vigorous and prompt diuresis, which may result in negative fluid balance. This may also result in significant adverse effects, including electrolyte imbalance, ototoxicity, and volume contraction. Prolonged use of loop diuretics may lead to loop diuretic resistance, a frequent observation in the ICU. Three general mechanisms are used to explain loop diuretic resistance: rebound sodium retention, postdiuretic effect, and diuretic braking. While very few agents have joined the armamentarium and no new strategies have been developed to deal with this phenomenon, several options are available to clinicians for managing loop diuretic resistance, including salt restriction, administration of i.v. loop diuretics, continuous infusion of loop diuretics, and combination therapy using loop diuretics and thiazides.

CONCLUSION

Loop diuretic resistance presents a challenge for clinicians in the ICU setting. Strategies to improve patients' responsiveness to these agents include fluid and salt restriction, switching from oral to i.v. loop diuretics, increasing diuretic dose, continuous infusion, and combination therapy with thiazides. Several of these strategies may be used concurrently to combat diuretic resistance and promote symptomatic relief of edema in the critically ill patient.

Consensus guidelines for oral dosing of primarily renally cleared medications in older adults

OBJECTIVES

To establish consensus oral dosing guidelines for primarily renally cleared medications prescribed for older adults.

DESIGN

Literature search followed by a two-round modified Delphi survey.

SETTING

A nationally representative survey of experts in geriatric clinical pharmacy.

PARTICIPANTS

Eleven geriatric clinical pharmacists.

MEASUREMENTS

After a comprehensive literature search and review by an investigative group of six physicians (2 general internal medicine, 2 nephrology, 2 geriatrics), 43 dosing recommendations for 30 medications at various levels of renal function were created. The expert panel rated its agreement with each of these 43 dosing recommendations using a 5-point Likert scale (1=strongly disagree to 5=strongly agree). Recommendation-specific means and 95% confidence intervals were estimated. Consensus was defined as a lower 95% confidence limit of greater than 4.0 for the recommendation-specific mean score.

RESULTS

The response rate was 81.8% (9/11) for the first round. All respondents who completed the first round also completed the second round. The expert panel reached consensus on 26 recommendations involving 18 (60%) medications. For 10 medications (chlorpropamide, colchicine, cotrimoxazole, glyburide, meperidine, nitrofurantoin, probenecid, propoxyphene, spironolactone, and triamterene), the consensus recommendation was not to use the medication in older adults below a specified level of renal function (e.g., creatinine clearance <30 mL/min). For the remaining eight medications (acyclovir, amantadine, ciprofloxacin, gabapentin, memantine, ranitidine, rimantadine, and valacyclovir), specific recommendations for dose reduction or interval extension were made.

CONCLUSION

An expert panel of geriatric clinical pharmacists was able to reach consensus agreement on a number of oral medications that are primarily renally cleared.

A thiazide test for the diagnosis of renal tubular hypokalemic disorders

Although the diagnosis of Gitelman syndrome (GS) and Bartter syndrome (BS) is now feasible by genetic analysis, implementation of genetic testing for these disorders is still hampered by several difficulties, including large gene dimensions, lack of hot-spot mutations, heavy workup time, and costs. This study evaluated in a cohort of patients with genetically proven GS or BS diagnostic sensibility and specificity of a diuretic test with oral hydrochlorothiazide (HCT test). Forty-one patients with GS (22 adults, aged 25 to 57; 19 children-adolescents, aged 7 to 17) and seven patients with BS (five type I, two type III) were studied; three patients with "pseudo-BS" from surreptitious diuretic intake (two patients) or vomiting (one patient) were also included. HCT test consisted of the administration of 50 mg of HCT orally (1 mg/kg in children-adolescents) and measurement of the maximal diuretic-induced increase over basal in the subsequent 3 h of chloride fractional clearance. All but three patients with GS but no patients with BS and pseudo-BS showed blunted (<2.3%) response to HCT; patients with BS and the two patients with pseudo-BS from diuretic intake had increased response to HCT. No overlap existed between patients with GS and both patients with BS and pseudo-BS. The response to HCT test is blunted in patients with GS but not in patients with BS or nongenetic hypokalemia. In patients with the highly selected phenotype of normotensive hypokalemic alkalosis, abnormal HCT test allows prediction with a very high sensitivity and specificity of the Gitelman genotype and may avoid genotyping.

Diuretics in pediatrics : current knowledge and future prospects

This review summarizes current knowledge on the pharmacology, pharmacokinetics, pharmacodynamics, and clinical application of the most commonly used diuretics in children. Diuretics are frequently prescribed drugs in children. Their main indication is to reduce fluid overload in acute and chronic disease states such as congestive heart failure and renal failure. As with most drugs used in children, optimal dosing schedules are largely unknown and empirical. This is undesirable as it can potentially result in either under- or over-treatment with the possibility of unwanted effects. The pharmacokinetics of diuretics vary in the different pediatric age groups as well as in different disease states. To exert their action, all diuretics, except spironolactone, have to reach the tubular lumen by glomerular filtration and/or proximal tubular secretion. Therefore, renal maturation and function influence drug delivery and consequently pharmacodynamics. Currently advised doses for diuretics are largely based on adult pharmacokinetic and pharmacodynamic studies. Therefore, additional pharmacokinetic and pharmacodynamic studies for the different pediatric age groups are necessary to develop dosing regimens based on pharmacokinetic and pharmacodynamic models for all routes of administration.

The Na+-excreting efficacy of indapamide in combination with furosemide in massive edema

BACKGROUND

Massive systemic edema is often observed in patients with severe nephrotic syndrome, including diabetic nephropathy. Although furosemide, a loop diuretic, is often administered to these patients, some patients do not respond to this treatment, still showing massive edema.

METHODS

The efficacy of indapamide which has a thiazide-like effect on distal convoluted tubules in combination with furosemide, was evaluated in eight patients with massive edema, in regard to both Na+ excretion and diuresis. Indapamide 2 mg was administered once a day, in the morning, to patients in whom it was considered that furosemide treatment of 40-120 mg a day for 1 week was ineffective.

RESULTS

Urinary Na+ excretion was markedly increased, from 83.7 +/- 82.2 mEq/day to 140.7 +/- 33.8 mEq/day after 1 week of the combination therapy compared with furosemide alone (P < 0.01); urine volume was also increased, from 1070 +/- 230 ml to 1359 +/- 296 ml after 1 week of the combination therapy (P < 0.05). In this context, body weight was significantly decreased, from 57.2 +/- 12.3 kg to 53.4 +/- 12.8 kg, after the combination therapy (P = 0.01). Indapamide in combination with furosemide was well tolerated, and no significant changes in serum levels of creatinine and potassium were observed.

CONCLUSIONS

This combination therapy appears to be effective in patients with massive edema, as it increased diuresis, and achieved potent Na+ excretion.

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.

Role of nitric oxide pathway in hypotensive and renal effects of furosemide during extracellular volume expansion

OBJECTIVE

In previous studies we demonstrated that the administration of furosemide associated with L-arginine contributes to enhanced hypotension and induces greater water than electrolyte excretion, in both normal and expansion conditions. The aim of the present study was to elucidate the interaction between furosemide and the nitric oxide (NO) system in renal and vascular responses during extracellular volume expansion.

DESIGN AND METHODS

Expanded [10% body weight (bw)] and non-expanded anaesthetized male Wistar rats were treated with furosemide (7.5 mg/kg bw). Mean arterial pressure, nitrite and nitrate excretion (NOx) were determined. NADPH-diaphorase activity, a marker of nitric oxide synthase (NOS) activity, was measured histochemically in different segments of the nephron, aorta and renal arteries. NOS activity was determined using an L-[U14C]-arginine substrate in the kidney and aorta of expanded and non-expanded rats, in basal conditions and after furosemide (10 micromol/l).

RESULTS

The hypotensive effect of furosemide was enhanced when NO production was stimulated in expanded and non-expanded animals. The diuretic treatment induced a significant increase in NOx excretion, in NADPH-diaphorase activity in the thick ascending limb of Henle, renal arteries and aorta, and in NOS activity in aorta and kidney in both groups.

CONCLUSIONS

Our results suggest that the hypotensive effect of furosemide may be attributed to NO-mediated vasodilation. The enhanced NOS activity, observed in the renal artery of furosemide-treated rats, could explain the increased renal plasma flow induced by furosemide. In addition, NO-pathway stimulation in the kidney could be one of the mechanisms by which furosemide exerts its diuretic and natriuretic effects, in control and in expansion conditions.

[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.

Achievement of target blood pressure levels in chronic kidney disease: a salty question?

A large body of evidence supports the validity of lowering blood pressure (BP) to prevent cardiovascular (CV) disease in the general population. This issue becomes even more critical in renal patients because they carry a greater CV risk across the entire spectrum of chronic kidney disease (CKD). In these patients, achievement of lower BP levels also is fundamental to limit the progression of renal damage, especially in the presence of significant proteinuria. Although expert panels have strongly recommended to intensively decrease BP in patients with CKD, management of hypertension in these patients remains inadequate. Armed with the knowledge of the extreme salt-sensitivity of BP in patients with CKD, it is reasonable to hypothesize that more aggressive treatment of volume expansion can be helpful. Nevertheless, although abundant literature has evidenced that dietary sodium restriction decreases BP levels in patients with essential hypertension, no large and prospective study has been conducted to date on this issue in patients with CKD. A potential reason is the low compliance of patients with CKD to dietary prescriptions; however, this problem can be overcome by specific counseling. Alternatively, loop diuretics administered at a high dose should represent the cornerstone of therapy, but, again, well-designed studies verifying the effectiveness of these agents in a large CKD population are still awaited. Nephrologists seem to be reluctant to adequately administer diuretics because of the fear of adverse events. Conversely, the major detrimental effect, that is, excessive hypovolemia, can be prevented if daily body weight loss is limited to 0.3 to 0.5 kg during the initial period of treatment.

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.

Metolazone and its role in edema management

Metolazone is commonly administered in conjunction with a loop diuretic to manage volume overload in patients otherwise resistant to loop diuretic therapy alone. Metolazone is a thiazide-type diuretic that is characterized by slow and sometimes erratic absorption when administered as the Zaroxylyn product. This absorptive profile together with the large volume of distribution and high degree of renal clearance for metolazone provide the pharmacologic basis for a favorable diuretic combination effect. Zaroxylyn should always be administered cautiously and only with a means of surveillance allowing the patient's weight to be carefully monitored so as to avoid excessive diuresis. If an excessive diuresis occurs with a metolazone and loop diuretic combination both drugs should be stopped temporarily. The temptation should be avoided to simply reduce the doses of either metolazone or the loop diuretic as a means to controlling an active diuresis.

Effects of L-arginine and furosemide on blood pressure and renal function in volume-expanded rats

1. The aim of the present study was to investigate the effects of L-arginine (L-Arg) on blood pressure and water and electrolyte excretion in control and extracellular fluid volume-expanded rats (10% bodyweight with 0.9% NaCl) and to determine whether diuretic treatment with furosemide (FUR) can be optimized by the administration of L-Arg in this model. 2. Both groups of animals were anaesthetized, divided into groups and treated with either 7.5 mg/kg FUR, 250 mg/kg L-Arg, 1 mg/kg NG-nitro-L-arginine methyl ester (L-NAME), FUR + L-NAME or FUR + L-Arg. Mean arterial pressure (MAP), diuresis, natriuresis and kaliuresis were determined. 3. Extracellular fluid volume expansion induced no changes in MAP in control and volume-expanded rats (92+/-6 vs 100+/-8 mmHg, respectively). The hypotension induced by FUR in control and volume-expanded rats (69+/-7 and 76+/-5 mmHg, respectively) was significantly (P < 0.01) enhanced by the administration of L-Arg (54+/-3 and 64+/-3 mmHg, respectively). 4. Injection of L-NAME increased MAP and diminished diuresis, natriuresis and kaliuresis in both groups. 5. Furosemide-induced water and electrolyte excretion was blunted by the administration of L-NAME. 6. The combination of L-Arg + FUR increased diuresis induced by FUR alone (control rats: 29.33+/-1.68 vs 12.91+/- 0.41 microL/min per 100 g, respectively; volume-expanded rats: 248.5+/-25.4 vs 112,6+/-8.3 microL/min per 100 g, respectively; P < 0.01). 7. The administration of the combination of L-Arg + FUR promoted a decrease in the sodium/water excretion ratio compared with the administration of FUR alone (control rats: 0.230+/-0.018 vs 0.45+/-0.03, respectively, P < 0.001; volume-expanded rats: 0.091+/-0.010 vs 0.22+/-0.03, respectively, P < 0.01). 8. The potassium/water excretion rate induced by FUR alone and in the presence of L-Arg followed a pattern similar to that seen for natriuresis (control rats: 0.35+/-0.05 vs 0.20+/-0.05 microEq/min per 100 g, respectively; volume-expanded rats: 0.045+/-0.008 vs 0.014+/-0.003 microEq/min per 100 g, respectively; P < 0.01). 9. The decrease in the electrolyte/water excretion ratio observed with FUR + L-Arg in volume-expanded rats was greater than in control animals. 10. The results of the present study show that the administration of FUR with L-Arg contributes to enhanced hypotensive and diuretic effects of FUR, thus diminishing the relative electrolyte excretion in normal conditions and in extracellular fluid volume expansion.

Pharmacology of diuretics

The diuretics in our therapeutic armamentarium have predictable effects based on their nephron sites of action. All but spironolactone must reach the lumen or urinary side of the nephron to exert their effects. Thus, in settings of decreased renal function, doses must be increased to deliver more diuretic into the urine. In other edematous disorders, such as congestive heart failure (CHF) and cirrhosis, adequate amounts of diuretic reach the site of action if renal function is satisfactory. Diminished response in these conditions is caused by a decrease in the sensitivity of the nephron to the diuretic, the mechanism of which is unknown. Rather than using large single doses of diuretic in CHF and cirrhosis, multiple doses and/or combinations of diuretics should be used. Therefore, thiazide diuretics coupled with loop diuretics are most logical because they affect different nephron sites and the thiazide counteracts distal nephron hypertrophy that may occur with loop diuretics alone. Ample studies have shown that such combinations can result in a truly synergistic response. Using pharmacokinetics and pharmacodynamics of diuretics, we can design therapeutic regimens in which satisfactory control of fluid and electrolyte homeostasis can be achieved in the vast majority of patients.

Treatment of edematous disorders with diuretics

Generalized edema results from alterations in renal sodium homeostasis that ultimately result in an expansion of extracellular fluid volume and accumulation of interstitial fluid. The common edematous disorders include congestive heart failure, cirrhosis, nephrotic syndrome, and renal insufficiency. The abnormalities of sodium homeostasis contributing to edema formation in each condition are discussed. Management of volume homeostasis, with an emphasis on the role of diuretic therapy, is reviewed.

Renal disease and hypertension in non-insulin-dependent diabetes mellitus

Recent epidemiologic data demonstrate a dramatic increase in the incidence of end-stage renal disease (ESRD) in patients with non-insulin-dependent diabetes mellitus (NIDDM), thus dispelling the mistaken belief that renal prognosis is benign in NIDDM. Currently, the leading cause of ESRD in the United States, Japan, and in most industrialized Europe is NIDDM, accounting for nearly 90% of all cases of diabetes. In addition to profound economic costs, patients with NIDDM and diabetic nephropathy have a dramatically increased morbidity and premature mortality. NIDDM-related nephropathy varies widely among racial and ethnic groups, genders and lifestyles; and gender may interact with race to affect the disease progression. While the course of insulin-dependent diabetes mellitus (IDDM) progresses through well-defined stages, the natural history of NIDDM is less well characterized. NIDDM patients with coronary heart disease have a higher urinary albumin excretion rate at the time of diagnosis and follow-up. This greater risk may also be associated with hypertension and hyperlipidemia, and genes involved in blood pressure are obvious candidate genes for diabetic nephropathy. Hyperglycemia appears to be an important factor in the development of proteinuria in NIDDM, but its role and the influence of diet are not yet clear. Tobacco smoking can also be deleterious to the diabetic patient, and is also associated with disease progression. Maintaining euglycemia, stopping smoking and controlling blood pressure may prevent or slow the progression of NIDDM-related nephropathy and reduce extrarenal injury. Treatment recommendations include early screening for hyperlipidemia, appropriate exercise and a healthy diet. Cornerstones of management should also include: (1) educating the medical community and more widely disseminating data supporting the value of early treatment of microalbuminuria; (2) developing a comprehensive, multidisciplinary team approach that involves physicians, nurses, diabetes educators and behavioral therapists; and (3) intensifying research in this field.

Diuretic treatment and diuretic resistance in heart failure

Diuretic therapy decreases capillary wedge pressure and improves New York Heart Association (NYHA) functional class both in acute and chronic heart failure. In advanced symptomatic heart failure, loop diuretics are generally necessary to improve symptoms of congestion. Diuretic resistance in the edematous patient has been defined as a clinical state in which diuretic response is diminished or lost before the therapeutic goal of relief from edema has been reached. The major causes of diuretic resistance are functional renal failure (prerenal azotemia), hyponatremia, altered diuretic pharmacokinetics, and sodium retention caused by counterregulatory mechanisms intended to reestablish the effective arterial blood volume. Therapeutic approaches to combat diuretic resistance include restriction of fluid and sodium intake, use of angiotensin-converting-enzyme (ACE) inhibitors, changes in route (oral, intravenous) and timing (single dose, multiple doses, continuous infusion) of diuretic therapy, and use of diuretic combinations.

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.