Interrelationships among thiazide diuretics and calcium, magnesium, sodium, and potassium balance in normal and hypertensive man

Antihypertensive and biochemical effects of different doses of hydrochlorothiazide alone or in combination with triamterene

The antihypertensive and biochemical effects of 25 mg hydrochlorothiazide alone or 50 mg hydrochlorothiazide alone or in combination with triamterene (either 37.5 or 75 mg) once daily were studied in 26 patients with essential hypertension. After a 5-week run-in period the patients were randomized to receive active therapy in a cross-over manner. Each treatment period lasted 3 months. All drugs significantly (p less than 0.01) lowered both systolic and diastolic blood pressure. There were no differences in blood pressure between the medication periods. Serum potassium concentration was slightly lower during all medication periods than during the run-in period. This change was statistically significant (p less than 0.01) only on 50 mg hydrochlorothiazide daily. There were no significant changes in serum magnesium during any of the periods compared to the run-in period. The lowest values were recorded on 50 mg hydrochlorothiazide alone and the highest on 50 mg hydrochlorothiazide plus 75 mg triamterene daily. A slight increase in serum urate was recorded in all medication periods compared to the run-in period. No significant changes were observed in serum total cholesterol, HDL cholesterol or triglycerides between any of the periods. It can be concluded that 25 mg of hydrochlorothiazide is as effective in lowering blood pressure as higher doses of the diuretic. Higher doses of thiazides will in some patients cause adverse metabolic reactions of which the fall in serum potassium and magnesium is effectively hindered by triamterene.

Southwestern Internal Medicine Conference: medical management of nephrolithiasis--a new, simplified approach for general practice

Considerable progress has been made regarding pathophysiology, diagnosis, and medical prevention of recurrent renal stone formation. The medical approach is not applied widely because of the availability of extracorporeal shockwave lithotripsy and the complexity of medical diagnostic and treatment modalities. In this review, a simplified program for the medical management of stones is described. From analysis of stone risk factors in 24-hour urine specimens, uncomplicated calcium stone disease is separated from other stone diseases. The uncomplicated calcium stone disease, comprising the illness in the majority of patients with recurrent renal calculi, is characterized by normocalcemia, normouricemia, calcium stones, and the absence of urinary tract infection, bowel disease, or marked hyperoxaluria. Uncomplicated calcium stone disease is separated into a hypercalciuric group and a normocalciuric group. In the simplified treatment program, the hypercalciuric group would be offered thiazide plus potassium citrate, whereas the normocalciuric group would receive potassium citrate alone.

Impairment of cardiac function by moderate potassium depletion

A previous study found that potassium depletion in dogs that resulted in a reduction in plasma potassium from 4.1 to 3.2 mmol/L was associated with impairment of many aspects of left ventricular mechanical function, including a 51% reduction in the peak rate of left ventricular filling. To determine if potassium depletion had similar effects in humans, cardiac function was assessed by Doppler and two-dimensional echocardiography in 10 normal volunteers following a 7-day period of potassium depletion, and again 7 days of potassium repletion. Potassium concentration for the group averaged 3.49 +/- 0.12 mmol/L after the depletion period, and 4.57 +/- 0.14 mmol/L after repletion. Early peak mitral flow velocity was significantly less during depletion than during repletion. The values at rest were 89.5 +/- 6.6 and 77.0 +/- 4.9 cm/s during repletion and depletion, respectively (P < .01). Isovolomic relaxation time and deceleration time of flow through the mitral valve were also significantly increased during potassium depletion. No other measured indices of cardiac function were affected by potassium depletion. The results suggest that in normal volunteers, moderate potassium depletion may impair active relaxation of the left ventricle to a degree that is clinically significant.

Do diuretics cause magnesium deficiency?

1. Controlled trials, of which there are few, do not substantiate claims that diuretics play a role in causing magnesium deficiency. Consequently, the vast majority of patients taking conventional doses of thiazide diuretics (i.e. bendrofluazide 2.5 mg day-1 or equivalent) do not need magnesium supplements. On balance, potassium-sparing diuretics tend to increase serum and intracellular magnesium content; this should not be taken as evidence of prior magnesium deficiency. It remains theoretically possible that large doses of loop diuretics given more than once daily for long periods could induce negative magnesium balance and magnesium deficiency. However, it has been difficult to run appropriately controlled trials in conditions where such therapy is needed (i.e. heart failure) and until more reliable information becomes available no absolute recommendation can be made. 2. Methods for the measurement of intracellular free magnesium levels are now available and are more relevant to the assessment of magnesium deficiency than total intracellular magnesium content; the complex relationship between intracellular free and total magnesium content remains to be defined. Future work involving the effect of diuretics on intracellular free magnesium measurements should make every attempt to avoid the errors of trial design and multiple publication that litter current and past literature.

Hypokalemia and cardiovascular disease

A growing body of experimental, epidemiologic and physiologic evidence testifies to the hazards of hypokalemia and other electrolyte disorders that can complicate the chronic use of diuretic drugs in patients with cardiovascular disease. This study reviews the complex renal and extrarenal mechanisms that regulate potassium balance in normal persons with special attention to the role of stress-related hormones. Disturbances of potassium balance are common in patients taking diuretics; indeed, the potential number of people in this country at risk of diuretic-related hypokalemia approaches 9 million. The magnitude of this problem is of particular concern, because of the compelling data that link hypokalemia in such patients to electrical instability of the heart and to a fatal outcome after an acute cardiac injury. Therefore, aggressive correction of hypokalemia is warranted in patients with cardiovascular disorders.

The role of dietary electrolytes in hypertension

The possible contribution of dietary electrolyte intake as a cause of or contributor to the development of hypertension has been intensively investigated for over 50 years. Evidence from various sources suggests a role for sodium-salt, chloride, calcium, and magnesium. In this article, we will review the evidence supporting a role for each of these electrolytes in human hypertension.

Decreased intracellular free magnesium in erythrocytes of spontaneously hypertensive rats

Using 31p-NMR (the phosphorus nuclear magnetic resonance) spectroscopy, we measured intracellular free Mg levels in the erythrocytes of untreated (n = 7) and diltiazem-treated spontaneously hypertensive rats (SHR) (n = 8), and compared them with age-matched Wistar-Kyoto rats (WKY) (n = 10). The intracellular free Mg levels were significantly (p less than 0.01) decreased in untreated SHR compared with those in control WKY. A successful antihypertensive treatment with diltiazem increased the intracellular free Mg levels compared with untreated SHR (p less than 0.05). Furthermore, an inverse correlation was observed between intracellular free Mg levels and blood pressure levels in all groups (r = -0.48, p less than 0.01, n = 25). These observations suggest that abnormalities of intracellular Mg metabolism may be, in part, related to the development or the maintenance of hypertension in SHR.

Renal actions of a uricosuric diuretic, racemic indacrinone, in man: comparison with ethacrynic acid and hydrochlorothiazide

The effects of indacrinone (IND) have been investigated in a two part study. First, a total of 36 clearance studies have been performed in 14 healthy volunteers, under conditions of either maximal hydration or hydropenia, to compare the renal sites of action of single oral doses of IND, 20 mg, ethacrynic acid (EA), 100 mg, and hydrochorothiazide (HCTZ), 100 mg. Under conditions of maximal water hydration, IND increased fractional Na+ excretion from a mean of 1.19 +/- 0.05 to 4.93 +/- 0.67% of GFR. This was similar to the response seen with HCTZ, which increased fractional Na+ clearance up to 3.16 +/- 0.17% of GFR; EA increased fractional Na+ excretion up to 14.5 +/- 2.5% of GFR. The mean reduction in fractional free-water clearance (CH2O/GFR X 100%) invoked by IND, (delta = -34.8% of control) was similar to that produced by EA, (delta = -27.2% of control), and by HCTZ, (delta = -26.6% of control). During hydropenia with superimposed mannitol diuresis, both IND and EA caused a fall in fractional free-water reabsorption (TcH2O/GFR X 100%), delta IND = -20.3% of control, delta EA = -70.1% of control. HCTZ produced a significant increase in fractional free-water reabsorption, delta HCTZ = -20.7% of control. In all studies, single doses of IND were both uricosuric and hypouricaemic. Fractional urate excretion increased from a mean 6.7 +/- 0.1 to 15.2 +/- 2.1% of GFR whilst plasma urate concentration fell from a mean of 0.36 +/- 0.03 to 0.34 +/- 0.03 mM (P less than 0.05) within 2-3 h post drug. HCTZ and EA, in single doses, had little effect on urate excretion. In the second part of the study, a total of 16 healthy volunteers received either IND, 10 mg, or HCTZ 50 mg, orally for 8 days, whilst on a diet of controlled electrolyte content. Both drugs were well tolerated by both sets of subjects with no adverse clinical or pathological findings. Both IND and HCTZ caused a significant reduction in weight and standing systolic blood-pressure during the first 48 h of therapy. At the doses administered, IND and HCTZ displayed similar diuretic responses with respect to water, Na+, Cl-, Ca2+ and PO4(3-) excretion. IND produced less kaliuresis than HCTZ during the first treatment day but cumulative K+ loss was similar for both drugs over the eight days of therapy. Fractional urate excretion after IND remained elevated throughout the 8 days of therapy and the subjects remained isouricaemic for 7 days.(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemical effects in patients with calcium oxalate stone disease during combined treatment with bendroflumethiazide and magnesium oxide

Thirteen patients with calcium oxalate stone disease were treated with 2.5 mg bendroflumethiazide and 200 mg magnesium oxide twice daily for 1 year, and the effects on serum and urine constituents were evaluated. Serum magnesium and potassium decreased, whereas urate increased during treatment. The association of decreased urinary calcium and increased urinary magnesium resulted in a reduced Ca/Mg quotient and apparently a lower risk of forming urine supersaturated with calcium oxalate. Combined treatment with a thiazide and magnesium appears to alter the composition of urine in a way that might be more favourable than treatment with either substance alone.

Mechanism of action, pharmacokinetics, adverse effects, and therapeutic uses of amiloride hydrochloride, a new potassium-sparing diuretic

Amiloride hydrochloride is a new, orally administered, potassium-sparing diuretic with mild natriuretic and diuretic properties. Its primary site of action is the distal tubule of the nephron where it selectively blocks sodium transport, thereby inhibiting sodium-potassium exchange. The mechanism of action of amiloride is independent of aldosterone. It is excreted unmetabolized in the urine and feces. Peak serum levels are seen at three hours, and the serum half-life is six hours. The drug can probably be safely administered to patients with hepatic dysfunction but should be used cautiously, if at all, in patients with renal insufficiency. Amiloride is well tolerated, and serious toxicity is rare. It should prove useful in edematous states and hypertension. When amiloride is used in fixed combination with a thiazide diuretic the risk of hypokalemia is minimal.

Hypotensive effects of xipamide in essential hypertension. Crossover comparison with hydrochlorothiazide

Twenty-nine patients with mild to severe essential hypertension were treated with titrated doses of xipamide, before or after treatment with 50 and , if necessary, 100 mg hydrochlorothiazide in a 13- to 25-week open crossover study. Based on supine diastolic pressure readings taken at weekly intervals, xipamide controlled hypertension in all subjects: 17 achieved control with a daily dose of 5 mg; seven, with 10 mg; and five, with 20 mg. In contrast, eight of the 29 patients could not be controlled with 100 mg/day hydrochlorothiazide. The only significant biochemical change observed was an increase in serum uric acid in 12 patients after hydrochlorothiazide but in only six patients after xipamide. Natriuresis was comparable after both drugs; 5 and 10 mg xipamide were as effective as 50 and 100 mg hydrochlorothiazide. The only side effect noted, cramping due to hypokalemia, occurred during treatment with hydrochlorothiazide, but not xipamide, and was reversed by potassium supplements.

Diuretic-induced ventricular ectopic activity

The need to avoid hypokalemia during diuretic therapy in nondigitalized patients has been questioned. Twenty-one patients with (1) mild essential hypertension, (2) plasma potassium of less than 3.5 meq/liter during previous diuretic treatment, and (3) normal findings [less than 6 unifocal ventricular premature beats/hour] on 24-hour ambulatory electrocardiographic monitoring and exercise testing were treated with hydrochlorothiazide (50 mg twice a day) for four weeks and then ambulatory electrocardiographic monitoring and exercise testing were repeated. Ambulatory electrocardiographic monitoring revealed that ventricular ectopic activity developed in seven patients and complex ventricular ectopic activity (multifocal ventricular premature beats, ventricular couplets and/or ventricular tachycardia) in four. Only two of these seven had ventricular ectopic activity during exercise testing while they were hypokalemic. Potassium repletion in these seven patients with spironolactone abolished complex ventricular ectopic activity and reduced unifocal ventricular premature beats significantly (p less than 0.01) from an average of 71.2 ventricular premature beats/hour/patient during hydrochlorothiazide treatment to 5.4 ventricular premature beats/hour/patient after potassium repletion. Although complex ventricular ectopic activity was more likely to occur with plasma potassium less than 3.0 meq/liter, restoration of normokalemia was required in several patients to abolish residual ventricular ectopic activity. Persistent ventricular ectopic activity in one patient suggested that myocardial injury sustained during hypokalemia may initiate chronic ventricular ectopic activity. Even in nondigitalized patients, the hazard of diuretic-induced ventricular ectopic activity warrants correction of hypokalemia.

Studies on the mechanism and characteristics of action of a uricosuric diuretic, indacrinone (MK-196)

1 The renal action of indacrinone (MK-196), a phenoxyacetic acid derivative with diuretic and uricosuric properties, has been studied in fifteen male subjects. 2 Increasing single doses of up to 60 mg of oral indacrinone produced a linear increase in urinary volume and excretion of Na+ and Cl-, whilst the responses of urinary K+, Ca2+, Mg2+ and uric acid excretion, rose to a plateau at the 40 mg dose. 3 Indacrinone evoked a rapid diuretic response which reached a maximum of 2-4 h and was largely complete at 8-12 h after administration. 4 During maximal hydration, indacrinone produced a substantial fall in fractional free water clearance (CH2O), from 8.89% to 5.83% of the filtered load of water, associated with an increase in osmolal clearance, from 1.38% to 5.78% of the filtered load of solute. The reduction in CH2O was of the same order as that produced by a dose of ethacrynic acid with comparable saluretic activity and significantly greater than that produced by an equi-saluretic dose of hydrochlorothiazide. These findings imply an action of indacrinone upon solute transport in the diluting segments of the distal tubule. 5 At the time of maximal indacrinone-induced saluresis, which amounted to an increase from 0.48% to 4.61% of the filtered load of NaCl, fractional urate clearance increased from 5.16% to 12.24% of the filtered load of uric acid. 6 Indacrinone is a long acting diuretic, sharing some properties in common with both loop diuretics and benzothiadiazines. The results are discussed in relation to structure-activity amongst derivatives of phenoxyacetic acid.

Effects of amiloride on arterial pressure and renal function

Amiloride was administered to 13 male patients with mild essential hypertension and normal renal function. It effectively reduced supine and standing arterial pressures. The antihypertensive response was associated with a significant decrease in renal inulin clearance and a rise in plasma creatinine concentration, although both values at the end of seven weeks of therapy remained within normal limits. Serum potassium concentrations rose but did not reach hyperkalemic levels. Amiloride did not increase blood levels of glucose, uric acid, lipids, calcium, or urea nitrogen. We conclude that amiloride is an effective antihypertensive and antikaliuretic agents for patients with mild hypertension and normal renal function.