[Renal effect of treatment for heart failure]

The case of a 66-year-old male with heart failure and cardiorenal syndrome is presented. The patient had normal renal function before intensive treatment with diuretics and ACE inhibitor. Shortly after the ACE inhibitor was stopped and diuretics were either stopped or reduced in dosage, his renal function normalized. Suggestions are presented for follow-up after initiation of ACE inhibitor treatment.

The evaluation of the diuretic action of parenteral formulations of metolazone

BACKGROUND AND OBJECTIVES

This study was design to compare the diuretic and natriuretic effects of the 2 parenteral formulations of metolazone and the combination of these 2 formulations of metolazone with the parenteral administration of furosemide. Metolazone is an anthracrene acid derivate and manifests a dual diuretic effect on the proximal and distal tubule with a minimal kaluretic effect. It is currently only marketed in an orally administrable formulation, and this has limited its utility in critically ill patients. Metolazone given orally and furosemide given orally or parenterally are frequently administrated together when furosemide alone is clinically inadequate at producing a desired diuresis.

METHODS

Sprague Dawley male rats (400 to 450 g) were divided into groups to receive a parenteral formulation of metolazone or furosemide administrated separately intraperitoneally (IP) or administrated IP in combination with one another. Tris buffer-administered IP was used as a control vehicle comparator. The urine volume voided over the following 24 hours was collected, measured and analyzed for sodium content.

RESULTS

Vehicle (Tris buffer) caused 9 +/- 1 mL/d output of urine with a sodium [Na+] concentration of 194 +/- 41 micromol/L (n=6 per group). Metolazone 2 mg/kg resulted in 16 +/- 3 mL/d urine output and sodium [Na+] of 278 +/- 76 micromol/L (n=6 per group). Furosemide 2, 4, and 6 mg/kg resulted in a volume of urine 9 +/- 1, 14 +/- 2 and 17 +/- 2 mL/d and [Na+] micromol/L of 194 +/- 41, 206 +/- 108, and 229 +/- 91, respectively. Metolazone 4 mg/kg combined with furosemide 4 mg/kg resulted in a urine volume of 21 +/- 1 mL/d and [Na+] of 326 +/- 108 micromol/L.

CONCLUSION

Combining metolazone and furosemide can cause an increase in urine volume and sodium excretion. Metolazone administrated parenterally in combination with the parenteral administration of furosemide appears to have an important clinical potential.

Pathophysiology of functional mutations of the thiazide-sensitive Na-Cl cotransporter in Gitelman disease

Most of the missense mutations that have been described in the human SLC12A3 gene encoding the thiazide-sensitive Na(+)-Cl(-) cotransporter (TSC, NCC, or NCCT), as the cause of Gitelman disease, block TSC function by interfering with normal protein processing and glycosylation. However, some mutations exhibit considerable activity. To investigate the pathogenesis of Gitelman disease mediated by such mutations and to gain insights into structure-function relationships on the cotransporter, five functional disease mutations were introduced into mouse TSC cDNA, and their expression was determined in Xenopus laevis oocytes. Western blot analysis revealed immunoreactive bands in all mutant TSCs that were undistinguishable from wild-type TSC. The activity profile was: wild-type TSC (100%) > G627V (66%) > R935Q (36%) = V995M (32%) > G610S (12%) > A585V (6%). Ion transport kinetics in all mutant clones were similar to wild-type TSC, except in G627V, in which a small but significant increase in affinity for extracellular Cl(-) was observed. In addition, G627V and G610S exhibited a small increase in metolazone affinity. The surface expression of wild-type and mutant TSCs was performed by laser-scanning confocal microscopy. All mutants exhibited a significant reduction in surface expression compared with wild-type TSC, with a profile similar to that observed in functional expression analysis. Our data show that biochemical and functional properties of the mutant TSCs are similar to wild-type TSC but that the surface expression is reduced, suggesting that these mutations impair the insertion of a functional protein into the plasma membrane. The small increase in Cl(-) and thiazide affinity in G610S and G627V suggests that the beginning of the COOH-terminal domain could be implicated in defining kinetic properties.

Difficulties of introducing the National Service Framework for heart failure into general practice in the UK

BACKGROUND

The National Service Framework (NSF) sets standards for the management of heart failure in the UK. Loop diuretics are commonly first prescribed in primary care. Some patients taking these drugs have heart failure and may benefit from other treatments including ACE inhibitors. Accurate diagnosis in primary care is essential for the aims of the NSF to be realised.

AIMS

To investigate loop diuretic prescribing in general practice, to analyse recorded clinical features, patient investigations and ACE inhibitor use in this population.

METHOD

One thousand three hundred and one patients taking loop diuretics were identified from prescription records of seven general practices. Demographic details, clinical features, investigations and drug treatments were extracted from patient records.

RESULTS

The prevalence of loop diuretic prescribing increased with age. Twenty percent of patients were attributed a diagnosis of heart failure but relevant clinical features were recorded in less than 50% of patient records. Open access echocardiography was used in 8.9% of patients. ACE inhibitors were prescribed in 39.8% of patients considered to have heart failure. 18.2% of these were taking the recommended target dose.

CONCLUSION

Loop diuretics are prescribed commonly, particularly in the elderly. There is no clear pattern of documented clinical features that leads to prescription of these drugs. Open access echocardiography is rarely used to aid diagnosis. ACE inhibitors are under-prescribed and under-dosed in patients diagnosed with heart failure in this study population.

Age- and gender-related use of low-dose drug therapy: the need to manufacture low-dose therapy and evaluate the minimum effective dose

OBJECTIVES

Low-dose drug therapy is promoted as a way to maximize benefit and minimize adverse drug effects when prescribing for older adults. This population-based study evaluates the age and sex-related use of two common therapies: thiazide diuretics, where evidence supports the use of low-dose therapy, and beta-blockers, where trials have not evaluated the minimum effective dose.

DESIGN

Using linked administrative databases we identified all of the 120,613 persons dispensed a thiazide diuretic therapy and 12,908 myocardial infarction survivors dispensed beta-blocker therapy in Canada's largest province. We used logistic regression models to study the association of age and sex with dispensing of low-dose thiazide diuretic and beta-blocker therapy at doses lower than evaluated in trials.

RESULTS

Of 120,613 older people dispensed a thiazide diuretic, 32,372 (26.8%) were dispensed a low dose. Patients 85 years of age or older, relative to the youngest group, were 30% more likely to be dispensed low-dose therapy (OR=1.31; 95% CI, 1.27 to 1.36; P < .001). Women were 8% more likely than men to be dispensed a low-dose thiazide diuretic (OR=1.08; 95% CI, 1.05 to 1.11; P < .001). Of 10,991 myocardial infarction survivors dispensed atenolol, metoprolol, propranolol, or timolol, 9458 (86.1%) were dispensed a lower-than-evaluated dose. Patients 85 years of age or older, relative to those in the youngest group, were more than twice as likely to be dispensed a lower-than-evaluated beta-blocker therapy dose (OR=2.28; 95% CI, 1.74 to 3.04; P < .001). No difference was noted in the use of beta-blocker therapy dose by sex (OR=1.0; 95% CI, .89 to 1.15; P = .95).

CONCLUSIONS

Low-dose thiazide diuretic therapy prescribed widely to older people, particularly those of advanced age and women. The vast majority of myocardial infarction survivors were dispensed beta-blocker therapy at lower-than-evaluated doses. These findings highlight the need to manufacture low-dose thiazide diuretic therapy and to evaluate the minimum effective dose of beta-blocker therapy.

Changes in body water compartments with diuretic therapy in infants with chronic lung disease

The effects of diuretic therapy on body water compartments were studied in preterm infants with chronic lung disease. Gestational age of the infants ranged from 24 to 28 weeks, while the median postnatal age at the time of study was 40 days. Infants were randomized to receive furosemide (1.0 mg/kg/day) alone (n = 5) or combined with metolazone (0.2 mg/kg/day, n = 7) for 4 consecutive days. Treatment in both groups produced a significant decrease (P < 0.05) in extracellular water (ECW) without changes in plasma volume, total body water or body weight. The decrease in ECW with furosemide (503 +/- 28 to 446 +/- 19 ml/kg initial body weight) was of similar magnitude to that seen with combined furosemide plus metolazone (522 +/- 30 to 454 +/- 15 ml/kg initial body weight). Water and electrolyte intakes were similar in both groups and unchanged over the course of the study. These findings suggest that in infants with chronic lung disease, diuretic therapy induces intercompartmental shifts in body water, ultimately decreasing interstitial water while preserving PV. Only combined treatment with furosemide plus metolazone produced a significant increase in urine output, confirming the increased efficacy of combination therapy in inducing diuresis.

Double-blind comparison of losartan, lisinopril, and metolazone in elderly hypertensive patients with previous angiotensin-converting enzyme inhibitor-induced cough

This study compared the incidence of cough with the angiotensin-converting enzyme (ACE) inhibitor lisinopril and the diuretic metolazone with angiotensin II receptor antagonist losartan in elderly hypertensive patients with previous histories of ACE inhibitor-induced cough. A randomized, double-blind, stratified, parallel-group comparison of lisinopril at 10 mg, losartan at 50 mg, and metolazone at 1 mg, each given once daily for a maximum of 10 weeks, was performed in four hypertension clinics in four centers in two countries. Cough was detected by a questionnaire (the primary end point) given to elderly patients with hypertension, and the cough frequency was quantified by a visual analog scale (a secondary end point). A total of 84 elderly patients with hypertension, all who were nonsmokers with ACe inhibitor-induced cough and were confirmed by lisinopril rechallenge then placebo dechallenge, were randomized to the three treatment groups. The incidence of cough with losartan (18%) was significantly lower than with lisinopril (97%) and similar to that for metolazone (21%). Cough frequency evaluated by the visual analog scale was significantly lower for losartan than for lisinopril and similar to that for metolazone. The specific, selective angiotensin II receptor antagonist losartan is associated with a decrease in the incidence of cough in patients with previous ACE inhibitor-induced cough.

[Metolazone in the treatment of advanced therapy-resistant dilated cardiomyopathy]

Ten patients (eight male/two female) with advanced dilated cardiomyopathy (NYHA III/IV) and a mean fractional shortening in two-dimensional echocardiogram of 20% (9 to 30%) and a mean sodium excretion of 21 mmol (8 to 40 mmol) per day, pretreated with digoxin, captopril and a mean frusemide-dose of 147 mg (80 to 500 mg) without an effective diuresis, were additional treated with 2.5 to 5 mg oral metolazone daily. All patients had a brisk diuresis within 24 hours and a mean weight loss of 8.9 kg (3 to 20 kg) until discharge. All patients improved considerably by additional metolazone-therapy. Seven patients developed a mild hyponatraemia (122 to 132 mmol/l), seven showed mild (greater than or equal to 3.2 mmol/l) and one had a serious hypokalaemia (2.8 mmol/l); spironolactone-pretreated patients developed no hypokalaemia. Notably none of the patients had serious blood pressure fluctuation or a deterioration of renal function. To avoid severe electrolyte-disturbances, additional metolazone-therapy should be practised in hospital, preferring low-dose metolazone and reducing frusemide-dose under careful biochemical monitoring after diuresis is started.

Metolazone in treatment of severe refractory congestive cardiac failure

17 patients with New York Heart Association (NYHA) class IV congestive cardiac failure, refractory to conventional treatment, were additionally treated with oral metolazone (1.25-10 mg daily). 12 improved sufficiently to be discharged from hospital (NYHA class II or III, mean weight loss 8.3 kg), 1 of whom died at home 4 weeks later. The other 5 patients were treated with intravenous dobutamine for 72 h; 2 responded (average weight loss 4.4 kg), and 2 responded to subsequent reintroduction of metolazone. 4 of these 5 patients died, 2 in hospital of acute myocardial infarction. Overall, 15 patients with very severe refractory cardiac failure improved sufficiently to be discharged from hospital. Treatment was associated with mild transient hypokalaemia in 7 patients, and hyponatraemia and renal impairment in 1, for whom metolazone dosage had to be reduced. Failure to respond to the introduction of metolazone may indicate an especially poor prognosis.

A comparison of combinations of diuretics in nephrotic edema

The metolazone-furosemide combination of diuretics was compared with the thiazide-furosemide combination in nephrotic patients with edema. Nine patients underwent a crossover, randomized study receiving furosemide (2 mg/kg per dose) and either metolazone (dose varied according to weight) or chlorothiazide (10 mg/kg per dose). An additive natriuretic and diuretic effect was observed after both metolazone and thiazide were combined with furosemide. The use of both types of diuretic combination was associated with marked kaliuresis. These combinations of diuretics seem equally effective in inducing natriuresis and diuresis in edematous nephrotic patients.

Combination of furosemide and metolazone in the treatment of severe congestive heart failure

Ten patients with severe congestive heart failure (6 women and 4 men, aged 67 +/- 4.35 years) were given diuretic therapy with either furosemide or metolazone followed by combined therapy of both agents. We found that the furosemide-metolazone combination induced greater natriuresis, urinary output and weight loss than did furosemide or metolazone alone. Notably, none of our patients displayed profound diuresis, severe hyponatremia or deterioration of renal function, found previously in high-risk patients treated with this combination.

Efficacy of metolazone and furosemide in children with furosemide-resistant edema

The effect of a combination of metolazone (0.2 to 0.4 mg/kg/d) and furosemide (2 to 4 mg/kg/d) in achieving a natriuresis and diuresis was measured in 14 children during 22 episodes of edema resistant to furosemide alone. Urinary volume increased from 24 +/- 14 mL/kg/d for patients receiving furosemide to 51 mL/kg/d with combined diuretic therapy (P less than .01), and sodium excretion increased from 34 +/- 5 mEq/d to 155 +/- 176 mEq/d (P less than .01). Two children with severe hypoalbuminemia (serum albumin level less than 1.5 g/dL) and normal renal function, and five children with chronic renal insufficiency (71%) did not respond to combined diuretic therapy. The combination of furosemide and metolazone offers a useful and effective oral therapy in most children with edema resistant to furosemide. Children with chronic renal insufficiency and furosemide-resistant edema did not respond to combination diuretic therapy.

Diuretic action of metolazone in dogs

Metolazone, the sulfonamide diuretic was investigated to determine the sites of action. We used a radioactive microsphere, clearance and stop-flow method in anesthetized dogs. Urine flow and urinary excretion of sodium and potassium were increased at 5--60 min when metolazone was given intravenously at doses of 0.2--5.0 mg/kg, while total renal blood flow, distribution of cortical renal blood flow and GFR did not change. The urinary excretion rate of sodium to potassium (Na/K) increased from 5.69 +/- 0.82 to 8.07 +/- 0.76 in a dose of 1.0 mg/kg, i.v. Osmolar clearance and free water reabsorption increased almost proportionally, indicating that metolazone has little effect on the medullary portion of the ascending limb of Henle and may have a proximal site of action. In stop-flow experiments, a significantly raised U/PNa/U/Pcreatinine was observed at the dip situated distally to the ascending limb of Henle. These findings indicate that the diuretic action of metolazone may be due to the inhibition of sodium reabsorption in the distal nephron segments, in addition to the absence of modification of the cortical regional blood flow.

[Pharmacological study on diuretic action of 2-methyl-3-(o-tolyl)-6-sulfamyl-7-chloro-1, 2, 3, 4-tetrahydro-4-quinazolinone (metolazone) (author's transl)]

Renal effects of metolazone (MET), a new diuretic agent, were compared with those of hydrochlorothiazide (HCT) in rats. MET in an oral dose of 0.01 approximately 0.5 mg/kg resulted in a dose-related increase in urine flow, sodium excretion and osmolal clearance in male rats. The natriuretic action of MET was not enhanced by administration of an increased dosage (1 approximately 5 mg/kg). Urinary excretion of potassium was significantly increased after MET, but was less than that of sodium. Therefore, the ratio of urinary concentration of sodium to potassium was markedly increased. Similar results were obtained when MET was intraperitoneally administered. In female rats, MET also proved to be an effective natriuretic. The diuretic effects of HCT were qualitatively similar to those of MET, but MET was 10--20 times as potent as HCT on a basis of minimal effective dose. In the renal clearance experiments, MET did not influence the renal plasma flow and glomerular filtration rate. From these findings, it is concluded that MET exerts a diuretic effect by inhibiting the reabsorption of electrolytes in the renal tubules.