Clinical pharmacologic implications in diuretic selection

Effect of short-term treatment with bumetanide, quinapril and low-sodium diet on dogs with moderate congestive heart failure

OBJECTIVE

To evaluate the effect of bumetanide, quinapril and a low-sodium diet on clinical response tolerance and side-effects on dogs with moderate congestive heart failure.

DESIGN

A prospective clinical study, using 32 client-owned dogs with naturally occurring disease.

PROCEDURE

Thirty-two dogs diagnosed with congestive heart failure (International Small Animal Cardiac Health Council stage II) due to mitral valve disease were included. During 4 weeks, patients received 0.5 mg/kg quinapril (Ectren, Menarini), 0.1 mg/kg bumetanide (Fordiuran, Boehringer Ingelheim) and a low sodium diet (CNM-CV, Purina) was fed. All dogs were examined weekly and results were treated statistically.

RESULTS

The treatment was safe, effective and well-tolerated and no major side-effects were observed. There were no significant changes in measured haematological and biochemical variables, including serum electrolyte concentrations and urinary fractional excretion of electrolytes.

CONCLUSION

This study suggests that the combined treatment with bumetanide, quinapril and low-sodium diet for controlling moderate CHF due to mitral insufficiency in dogs is simple, easy-to-administer and effective in controlling clinical signs and prompting improvement even after short-term treatment.

Reversing oliguria in critically ill patients

Oliguria is a common occurrence in the ICU setting. In patients with preserved renal function, fluid challenges or low doses of diuretics are generally successful. In patients with oliguric renal failure, it is still essential to ensure adequate intravascular fluid volume, especially in critically ill patients. Loop diuretics remain the mainstay of treatment. When diuretic resistance is encountered, physicians should consider further optimization of hemodynamics, alternative loop diuretics, and combined drug therapy. In some cases, continuous renal replacement therapy can be very effective. Yet, while these interventions can help reduce the morbidity of severe volume overload, they have not been shown to improve mortality rates.

Addition of a thiazide: an effective remedy for furosemide resistance after cardiac operations

BACKGROUND

The frequent use of diuretic drugs in cardiac surgical practice contrasts with the lack of documentation regarding diuretic treatment in this setting. The aims of this study were to delineate the need for diuretic drugs in adult cardiac surgical practice and to evaluate the impact of adding a combination of 50 mg hydrochlorothiazide and 5 mg amiloride orally to patients responding poorly to furosemide.

METHODS

Two hundred ten consecutive patients, 159 undergoing coronary artery bypass grafting procedures and 51 having valve operations, were studied.

RESULTS

Seventy-seven patients received large doses of furosemide (> or = 80 mg/24 h) at some time during the postoperative course, and of these 20 responded poorly to furosemide (weight loss 0.3 +/- 0.2 kg) despite considerable fluid retention. The addition of hydrochlorothiazide and amiloride provided a prompt and effective remedy to relative furosemide resistance. Average weight loss was 2.3 +/- 0.2 kg (p < 0.01 compared with response to furosemide) and average diuresis was 2,949 +/- 156 mL in the following 24 hours.

CONCLUSIONS

Relative furosemide resistance is common after cardiac operations. Thiazides, although they are mild diuretic agents, may serve as useful adjuncts in this setting.

Clinicopharmacological reappraisal of the potency of diuretics

From a clinicopharmacological standpoint, the urinary excretory potency of diuretics should be assessed comparatively on the basis of the changes in 24-hour natriuresis, with respect to 24-hour natriuresis after placebo, caused by single oral doses administered to healthy adult subjects who are in habitual and steady-state external sodium balance. The potency of various formulations of loop (e.g., furosemide), of early distal tubular (e.g., the thiazides), and of potassium-retaining diuretics, as well as of several combinations of diuretics, has been evaluated in a series of studies. Two formulations of loop diuretics (muzolimine 20 mg and torasemide 2.5 mg) are definitely nondiuretic. The majority of the other formulations of loop diuretics studied are, in general, comparatively less potent than most of the common formulations of early distal tubular diuretics studied. As a general rule, most common formulations of early distal tubular diuretics are at least not less potent than the majority of common formulations of loop diuretics. Hydrochlorothiazide 25 mg and furosemide 80 mg have similar potencies. Loop diuretics increase mean renal sodium output strikingly within the first few (0-6) hours after dosing, but this forced excretion is followed by a rebound with respect to postplacebo mean urinary sodium flow; the rebound usually takes place between 6 and 24 hours after dosing. However, no rebound in mean urinary sodium flow occurs during the 24 hours following a single dose of a distal tubular diuretic; these substances increase urinary sodium excretion with lower maximal intensity but more protractedly than loop diuretics.(ABSTRACT TRUNCATED AT 250 WORDS)

Diuretics in the therapy of hypertension: current status

Diuretics were the first effective oral agents for treating hypertension. They have proven to be safe and effective. Recently, they have been scrutinized as possibly being responsible for certain side effects that may increase risk for cardiovascular morbidity and mortality. A careful review of the literature suggests this class of agents warrants continued use as first-line therapy of hypertension, especially in certain demographic groups. However, monitoring of potential baleful effects and a general reduction in dosage are appropriate. Furthermore, selection of other (alternative) agents for monotherapy is advised in certain clinical circumstances.

Efficacy of low-dose captopril in addition to furosemide and spironolactone in patients with decompensated liver disease during blunted diuresis

The renin-angiotensin-aldosterone system is activated by diuretics and involved in the diuretic resistance of cirrhotic patients with ascites and oedema. In previous studies relatively high doses of captopril (25-400 mg daily) were unsuccessful in promoting diuresis and natriuresis in these patients. We analyzed the efficacy of a low dose of captopril in eight patients with massive ascites resistant to therapy of salt/fluid restriction and increasing doses of spironolactone and furosemide. Mean duration of diuretic use was 73 days (range 7-240 days). After at least 3 days of observation on 80 mg furosemide and 100 mg spironolactone only, captopril was added. Four out of eight patients responded with an increase in natriuresis and diuresis; daily dose of captopril was 20.6 mg in responders and 26.5 mg in non-responders. After the addition of captopril the mean weight change was -7.5 kg in responders and +0.25 kg in non-responders. Mean urinary sodium output in responders increased from 72.8 (S.D. = 35.2) to 128.5 (63.5) mmol within 10 days. Increased diuresis in responders made diuretic reduction necessary: mean furosemide from 80 to 53.3 mg, and mean spironolactone from 100 to 68.1 mg. Creatinine clearances remained stable. High levels of plasma renin activity, plasma aldosterone and angiotensin-II were found in all patients. Non-responders showed more severe hyponatremia and higher vasopressin levels. Natriuretic atrial factor (NAF) was in the upper-normal range or slightly elevated in both groups. In non-responders we noticed low levels of cGMP in 24-h urine, compared with responders.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of diuretics on outputs and flows of urine and urinary solutes in healthy subjects

The effects of single oral doses of common formulations of diuretics (i.e. formulations on the market or designed to be marketed) on 24-hour diuresis and natriuresis in healthy subjects are considered as a measure of the renal excretory potency of diuretics. Common formulations of distal tubular diuretics (e.g. hydrochlorothiazide 25mg, xipamide 10mg and 20mg) are more potent diuretics and natriuretics than common formulations of loop diuretics [e.g. furosemide (frusemide) 40mg, torasemide 2.5, 5 and 10mg]. Indeed, some common formulations of loop diuretics, such as torasemide 2.5, do not increase 24-hour diuresis or natriuresis in healthy subjects. 24-hour kaliuresis and magnesiuresis are elevated by common formulations of distal tubular diuretics, but they are only slightly increased or (more usually) not affected by common formulations of loop diuretics, when single doses are administered to healthy individuals. Common formulations of loop diuretics have lower diuretic and natriuretic potency and lower kaliuretic and magnesiuretic effects than common formulations of distal tubular diuretics, because the pronounced elevations in urinary excretions caused by loop diuretics during the first 6 hours after dosing are followed by rebounds, with respect to post-placebo excretions, between 6 and 24 hours after dosing. These rebounds, which affect the urinary flows of fluid, chloride, sodium, potassium and magnesium, do not occur after administration of common formulations of distal tubular diuretics, at least during the first 24 hours after administration of single doses to healthy subjects. The time courses of urinary excretions after loop diuretics are dose dependent. Higher doses produce more rapid changes in the urinary flows of fluid, chloride, sodium, potassium and magnesium than lower doses, to the extent that single administration of torasemide 2.5 or 5mg to healthy subjects is followed by urinary fluid and solute flows whose time courses resemble those after administration of hydrochlorothiazide 25mg.

Effect of high-dose furosemide in refractory congestive heart failure

High-dose firosemide is considered effective in primary renal sodium retention but is not generally recommended in congestive heart failure. In order to evaluate efficacy and safety of high-dose furosemide (greater than 500 mg/day), the authors studied 20 patients (pts) resistant to therapy (including furosemide less than 500 mg/day) selected from 161 pts admitted for chronic heart failure. All refractory pts (15 men and 5 women, mean age sixty +/- 12 years) were in NYHA class IV and showed hyponatremia (130 +/- 5 mEq/L) and impaired renal function (BUN 31 +/- 14 mg/dL, serum creatinine 1.3 +/- 0.3 mg/dL and BUN/creatinine ratio 23 +/- 7). In addition to digitalis, dopamine, angiotensin-converting enzyme inhibitors, or vasodilators, IV high-dose furosemide (775 +/- 419 mg/day, 500-2000) was given for ten +/- five days under daily clinical and laboratory monitoring. Three pts died of low-output syndrome while 16 pts were upgraded to NYHA class III and 1 pt to class II; a mean weight reduction of 7.3 +/- 2.9 kg in ten + five days (0.80 +/- 0.4 kg/day) and a mean diuresis increase of 88 +/- 57% occurred. The maximal dose of furosemide did not correlate with serum creatinine but did correlate with BUN/creatinine ratio (r = 0.78, p less than .001). Pts were discharged on with chronic heart failure, and 43% in the subgroup in NYHA class IV with hyponatremia. High dose furosemide was effective for rapid removal of excess water and salt in "furosemide-resistant" congestive heart failure. The relationship between renal impairment and maximal furosemide doses seems to confirm the role of renal pharmacokinetics in the appearance of furosemide resistance.