Amiloride, spironolactone, and potassium chloride in thiazide-treated hypertensive patients

Personalized Treatment of Patients With Primary Aldosteronism

Primary aldosteronism (PA) is a highly prevalent yet underdiagnosed secondary cause of hypertension. PA is associated with increased cardiovascular and renal morbidity compared with patients with primary hypertension. Thus, prompt identification and targeted therapy of PA are essential to reduce cardiovascular and renal morbidity and mortality in a large population with hypertension. Unilateral adrenalectomy is preferred for lateralized PA as the only potentially curative therapy. Surgery also mitigates the risk of cardiovascular and renal complications associated with PA. Targeted medical therapy, commonly including a mineralocorticoid receptor antagonist, is offered to patients with bilateral PA and those who are not surgical candidates. Novel therapies, including nonsteroidal mineralocorticoid receptor antagonists and aldosterone synthase inhibitors, are being developed as alternative options for PA treatment. In this review article, we discuss how to best individualize therapy for patients with PA.

Diagnosis and treatment of primary aldosteronism

Primary aldosteronism is a common cause of secondary hypertension associated with excess cardiovascular morbidities. Primary aldosteronism is underdiagnosed because it does not have a specific, easily identifiable feature and clinicians can be poorly aware of the disease. The diagnostic investigation is a multistep process of screening, confirmatory testing, and subtype differentiation of unilateral from bilateral forms for therapeutic management. Adrenal venous sampling is key for reliable subtype identification, but can be bypassed in patients with specific characteristics. For unilateral disease, surgery offers the possibility of cure, with total laparoscopic unilateral adrenalectomy being the treatment of choice. Bilateral forms are treated mainly with mineralocorticoid receptor antagonists. The goals of treatment are to normalise both blood pressure and excessive aldosterone production, and the primary aims are to reduce associated comorbidities, improve quality of life, and reduce mortality. Prompt diagnosis of primary aldosteronism and the use of targeted treatment strategies mitigate aldosterone-specific target organ damage and with appropriate patient management outcomes can be excellent. Advances in molecular histopathology challenge the traditional concept of primary aldosteronism as a binary disease, caused by either a unilateral aldosterone-producing adenoma or bilateral adrenal hyperplasia. Somatic mutations drive autonomous aldosterone production in most adenomas. Many of these same mutations have been identified in nodular lesions adjacent to an aldosterone-producing adenoma and in patients with bilateral disease. In addition, germline mutations cause rare familial forms of aldosteronism (familial hyperaldosteronism types 1-4). Genetic testing for inherited forms in suspected cases of familial hyperaldosteronism avoids the burdensome diagnostic investigation in positive patients. In this Review, we discuss advances and future management approaches in the diagnosis of primary aldosteronism.

A short review of primary aldosteronism in a question and answer fashion

OBJECTIVES

The aim of this study was to present up to date information concerning the diagnosis and treatment of primary aldosteronism (PA). PA is the most common cause of endocrine hypertension. It has been reported up to 24% of selective referred hypertensive patients.

METHODS

We did a search in Pub-Med and Google Scholar using the terms: PA, hyperaldosteronism, idiopathic adrenal hyperplasia, diagnosis of PA, mineralocorticoid receptor antagonists, adrenalectomy, and surgery. We also did cross-referencing search with the above terms. We had divided our study into five sections: Introduction, Diagnosis, Genetics, Treatment, and Conclusions. We present our results in a question and answer fashion in order to make reading more interesting.

RESULTS

PA should be searched in all high-risk populations. The gold standard for diagnosis PA is the plasma aldosterone/plasma renin ratio (ARR). If this test is positive, then we proceed with one of the four confirmatory tests. If positive, then we proceed with a localizing technique like adrenal vein sampling (AVS) and CT scan. If the lesion is unilateral, after proper preoperative preparation, we proceed, in adrenalectomy. If the lesion is bilateral or the patient refuses or is not fit for surgery, we treat them with mineralocorticoid receptor antagonists, usually spironolactone.

CONCLUSIONS

Primary aldosteronism is the most common and a treatable case of secondary hypertension. Only patients with unilateral adrenal diseases are eligible for surgery, while patients with bilateral and non-surgically correctable PA are usually treated by mineralocorticoid receptor antagonist (MRA). Thus, the distinction between unilateral and bilateral aldosterone hypersecretion is crucial.

Mineralocorticoid Receptor Antagonists for Treatment of Hypertension and Heart Failure

Spironolactone and eplerenone are both mineralocorticoid-receptor antagonists. These compounds block both the epithelial and nonepithelial actions of aldosterone, with the latter assuming increasing clinical relevance. Spironolactone and eplerenone both affect reductions in blood pressure either as mono- or add-on therapy; moreover, they each afford survival benefits in diverse circumstances of heart failure and the probability of renal protection in proteinuric chronic kidney disease. However, as use of mineralocorticoid-blocking agents has expanded, the hazards inherent in taking such drugs have become more apparent. Whereas the endocrine side effects of spironolactone are in most cases little more than a cosmetic annoyance, the potassium-sparing effects of both spironolactone and eplerenone can prove disastrous, even fatal, if sufficient degrees of hyperkalemia emerge. For most patients, however, the risk of developing hyperkalemia in and of itself should not discourage the sensible clinician from bringing these compounds into play. Hyperkalemia should always be considered a possibility in patients receiving either of these medications; therefore, anticipatory steps should be taken to minimize the likelihood of its occurrence if long-term therapy of these agents is being considered.

Comparison of single and combination diuretics on glucose tolerance (PATHWAY-3): protocol for a randomised double-blind trial in patients with essential hypertension

INTRODUCTION

Thiazide diuretics are associated with increased risk of diabetes mellitus. This risk may arise from K(+)-depletion. We hypothesised that a K(+)-sparing diuretic will improve glucose tolerance, and that combination of low-dose thiazide with K(+)-sparing diuretic will improve both blood pressure reduction and glucose tolerance, compared to a high-dose thiazide.

METHODS AND ANALYSIS

This is a parallel-group, randomised, double-blind, multicentre trial, comparing hydrochlorothiazide 25-50 mg, amiloride 10-20 mg and combination of both diuretics at half these doses. A single-blind placebo run-in of 1 month is followed by 24 weeks of blinded active treatment. There is forced dose-doubling after 3 months. The Primary end point is the blood glucose 2 h after oral ingestion of a 75 g glucose drink (OGTT), following overnight fasting. The primary outcome is the difference between 2 h glucose at weeks 0, 12 and 24. Secondary outcomes include the changes in home systolic blood pressure (BP) and glycated haemoglobin and prediction of response by baseline plasma renin. Eligibility criteria are: age 18-79, systolic BP on permitted background treatment ≥ 140 mm Hg and home BP ≥ 130 mm Hg and one component of the metabolic syndrome additional to hypertension. Principal exclusions are diabetes, estimated-glomerular filtration rate <45 mL/min, abnormal plasma K(+), clinic SBP >200 mm Hg or DBP >120 mm Hg (box 2). The sample size calculation indicates that 486 patients will give 80% power at α=0.01 to detect a difference in means of 1 mmol/L (SD=2.2) between 2 h glucose on hydrochlorothiazide and comparators.

ETHICS AND DISSEMINATION

PATHWAY-3 was approved by Cambridge South Ethics Committee, number 09/H035/19. The trial results will be published in a peer-reviewed scientific journal.

TRIAL REGISTRATION NUMBERS

Eudract number 2009-010068-41 and clinical trials registration number: NCT02351973.

Outcomes of drug-based and surgical treatments for primary aldosteronism

Treatments for primary aldosteronism (PA) aim to correct or prevent the deleterious consequences of hyperaldosteronism: hypertension, hypokalemia, and direct target organ damage. Patients with unilateral PA considered fit for surgery can undergo laparoscopic adrenalectomy, which significantly decreases blood pressure (BP) and medications in most cases and cures hypertension in about 40%. Mineralocorticoid receptor antagonists (MRA) are used to treat patients with bilateral PA and those with unilateral PA if surgery is not possible or not desired. Spironolactone is more potent than eplerenone, but high doses are poorly tolerated in men. MRA can be replaced or complemented with epithelial sodium channel blockers, such as amiloride. Thiazide diuretics and calcium channel blockers are used when the first-line drugs are insufficient to control BP. Dietary sodium restriction should be implemented in all cases because the deleterious consequences of hyperaldosteronism are dependent on salt loading. Several studies comparing the results of surgery and MRA have reported no differences in terms of BP, serum potassium concentration, or cardiovascular and kidney outcomes, although the benefits of treatment tend to be observed sooner with surgery. Patients with PA display relative glomerular hyperfiltration, which is reversed by specific treatment, revealing CKD in 30% of patients. However, further kidney damage is lessened by the treatment of PA.

Pathophysiology, diagnosis, and treatment of mineralocorticoid disorders

The renin-angiotensin-aldosterone system (RAAS) is a major regulator of blood pressure control, fluid, and electrolyte balance in humans. Chronic activation of mineralocorticoid production leads to dysregulation of the cardiovascular system and to hypertension. The key mineralocorticoid is aldosterone. Hyperaldosteronism causes sodium and fluid retention in the kidney. Combined with the actions of angiotensin II, chronic elevation in aldosterone leads to detrimental effects in the vasculature, heart, and brain. The adverse effects of excess aldosterone are heavily dependent on increased dietary salt intake as has been demonstrated in animal models and in humans. Hypertension develops due to complex genetic influences combined with environmental factors. In the last two decades, primary aldosteronism has been found to occur in 5% to 13% of subjects with hypertension. In addition, patients with hyperaldosteronism have more end organ manifestations such as left ventricular hypertrophy and have significant cardiovascular complications including higher rates of heart failure and atrial fibrillation compared to similarly matched patients with essential hypertension. The pathophysiology, diagnosis, and treatment of primary aldosteronism will be extensively reviewed. There are many pitfalls in the diagnosis and confirmation of the disorder that will be discussed. Other rare forms of hyper- and hypo-aldosteronism and unusual disorders of hypertension will also be reviewed in this article.

Aldosterone synthase inhibition: cardiorenal protection in animal disease models and translation of hormonal effects to human subjects

Background

Aldosterone synthase inhibition provides the potential to attenuate both the mineralocorticoid receptor-dependent and independent actions of aldosterone. In vitro studies with recombinant human enzymes showed LCI699 to be a potent, reversible, competitive inhibitor of aldosterone synthase (K_i = 1.4 ± 0.2 nmol/L in humans) with relative selectivity over 11β-hydroxylase.

Methods

Hormonal effects of orally administered LCI699 were examined in rat and monkey in vivo models of adrenocorticotropic hormone (ACTH) and angiotensin-II-stimulated aldosterone release, and were compared with the mineralocorticoid receptor antagonist eplerenone in a randomized, placebo-controlled study conducted in 99 healthy human subjects. The effects of LCI699 and eplerenone on cardiac and renal sequelae of aldosterone excess were investigated in a double-transgenic rat (dTG rat) model overexpressing human renin and angiotensinogen.

Results

Rat and monkey in vivo models of stimulated aldosterone release predicted human dose– and exposure–response relationships, but overestimated the selectivity of LCI699 in humans. In the dTG rat model, LCI699 dose-dependently blocked increases in aldosterone, prevented development of cardiac and renal functional abnormalities independent of blood pressure changes, and prolonged survival. Eplerenone prolonged survival to a similar extent, but was less effective in preventing cardiac and renal damage. In healthy human subjects, LCI699 0.5 mg selectively reduced plasma and 24 h urinary aldosterone by 49 ± 3% and 39 ± 6% respectively (Day 1, mean ± SEM; P < 0.001 vs placebo), which was associated with natriuresis and an increase in plasma renin activity. Doses of LCI699 greater than 1 mg inhibited basal and ACTH-stimulated cortisol. Eplerenone 100 mg increased plasma and 24 h urinary aldosterone while stimulating natriuresis and increasing renin activity. In contrast to eplerenone, LCI699 increased the aldosterone precursor 11-deoxycorticosterone and urinary potassium excretion.

Conclusions

These results provide new insights into the cardiac and renal effects of inhibiting aldosterone synthase in experimental models and translation of the hormonal effects to humans. Selective inhibition of aldosterone synthase appears to be a promising approach to treat diseases associated with aldosterone excess.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0340-9) contains supplementary material, which is available to authorized users.

Discovery and in Vivo Evaluation of Potent Dual CYP11B2 (Aldosterone Synthase) and CYP11B1 Inhibitors

Aldosterone is a key signaling component of the renin-angiotensin-aldosterone system and as such has been shown to contribute to cardiovascular pathology such as hypertension and heart failure. Aldosterone synthase (CYP11B2) is responsible for the final three steps of aldosterone synthesis and thus is a viable therapeutic target. A series of imidazole derived inhibitors, including clinical candidate 7n, have been identified through design and structure-activity relationship studies both in vitro and in vivo. Compound 7n was also found to be a potent inhibitor of 11β-hydroxylase (CYP11B1), which is responsible for cortisol production. Inhibition of CYP11B1 is being evaluated in the clinic for potential treatment of hypercortisol diseases such as Cushing's syndrome.

Aldosterone-receptor antagonism in hypertension

The role of the renin-angiotensin-aldosterone system (RAAS) in hypertension has since long been recognized and aldosterone has been acknowledged as one of the key hormones in the pathophysiology, not only in primary aldosteronism but also in essential hypertension and drug-resistant hypertension. Aldosterone-receptor antagonists (ARAs) are increasingly used in patients with resistant hypertension, often with impressive results. However, definitive evidence for the benefit of ARAs in these patients from randomized, controlled trials is lacking. This review gives an overview of the current data on this topic. Future studies should focus on the identification of factors that are able to predict the response to treatment, as to select patients who will benefit most from treatment with ARAs. On the basis of the current knowledge, we recommend prescription of ARAs to patients with primary aldosteronism, resistant hypertension and patients with hypertension and hypokalemia.

Low-dose spironolactone in the management of resistant hypertension: a surveillance study

METHODS

We have conducted an open observational study of the use of spironolactone 25-50 mg in the management of patients with resistant hypertension. This drug was recommended in 133 patients who were already receiving an angiotensin-blocking drug in addition to other therapies.

RESULTS

Of these, three defaulted from follow-up and 11 could not tolerate spironolactone. We therefore have outcome data on 119 patients. The addition of spironolactone (median dose 25 mg) was associated with a mean (SD) fall in systolic blood pressure of 21.7 mmHg (24.0; P < 0.001) and diastolic blood pressure of 8.5 mmHg (14.9; P < 0.001). In two patients spironolactone had to be discontinued on account of a rise of serum potassium to above 6.0 mmol/l, whereas overall the mean increase in serum potassium was 0.3 mmol/l.

CONCLUSION

With careful monitoring of plasma electrolytes, spironolactone at a low dose is an effective add-in drug in patients with hypertension resistant to a regime that includes an angiotensin-blocking agent.

The risks and benefits of aldosterone antagonists

Spironolactone and eplerenone are mineralocorticoid- blocking agents used for their ability to block a host of epithelial and nonepithelial actions of aldosterone. These compounds are of proven benefit in reducing blood pressure and urine protein excretion, and in conferring cardiovascular gain in diverse circumstances of heart failure. However, as enthusiasm grows for use of mineralocorticoid-blocking agents, the risks inherent to use of such drugs become more pertinent. Whereas the endocrine side effects of spironolactone are in reality little more than a cosmetic disfigurement, the potassium-sparing properties of spironolactone and eplerenone can prove life-threatening if hyperkalemia develops. However, for most patients the risk of developing hyperkalemia should not dissuade the prudent clinician from use of these compounds. Hyperkalemia should be considered as a possibility in any patient receiving these medications and as such is best addressed preemptively.

Pharmacokinetics and Pharmacodynamics of Mineralocorticoid Blocking Agents and their Effects on Potassium Homeostasis

Spironolacotone and eplerenone are mineralocorticoid-blocking agents used for their ability to block both the epithelial and non-epithelial actions of aldosterone. Spironolactone is a non-selective mineralocorticoid receptor antagonist with moderate affinity for both progesterone and androgen receptors. The latter property increases the likelihood of endocrine side effects with spironolactone including loss of libido, menstrual irregularities, gynecomastia and impotence. Eplerenone is a next generation aldosterone receptor antagonist selective for aldosterone receptors alone. This lesser affinity for progesterone and androgen receptors was arrived at by replacing the 17-alpha -thioacetyl group of spironolactone with a carbomethoxy group. Eplerenone is further distinguished from spironolactone by its shorter half-life and the fact that it does not have any active metabolites. Both eplerenone and spironolactone are effective antihypertensive agents and each has been shown to improve the morbidity and mortality of heart failure. Eplerenone or spironolactone use can increase serum potassium values and occasionally results in clinically relevant hyperkalemia. This is more apt to occur with spironolactone due to the very long half-life of several of its active metabolites.

Aldosterone antagonist facilitates the cardioprotective effects of angiotensin receptor blockers in hypertensive rats

BACKGROUND

There is increasing evidence to support the importance of blocking aldosterone to prevent target-organ damage in hypertension. We recently demonstrated an aldosterone breakthrough phenomenon during administration of an angiotensin type 1 receptor blocker (ARB).

OBJECTIVE

To elucidate the pathophysiological significance of residual aldosterone by investigating the influence of the aldosterone antagonist on the cardioprotective effects of the ARB in hypertensive rats.

METHODS

Injection vehicle alone, ARB (1.0 mg/kg per day candesartan by mouth), aldosterone antagonist (10 mg/kg per day spironolactone, subcutaneously), or combined treatment were administered to male stroke-prone spontaneously hypertensive rats for 24 weeks from the age of 4 weeks. Blood pressure, plasma angiotensin II and aldosterone concentrations, left ventricular weight, expression of type I and type III collagen mRNA, and histological findings were determined.

RESULTS

In the ARB-treated group, aldosterone concentrations remained unchanged (1.10 +/- 0.20 nmol/l, compared with 1.17 +/- 0.46 nmol/l in the control group), whereas systolic blood pressure (178 +/- 9 mmHg), left ventricular weight (0.372 +/- 0.035 g/100 g body weight), expression of collagen mRNA, and cardiac interstitial and perivascular fibrosis all decreased significantly compared with the control group (systolic blood pressure: 222 +/- 10 mmHg, P < 0.05; left ventricular weight: 0.483 +/- 0.021 g/100 g body weight, P < 0.05). Although blood pressure (217 +/- 9 mmHg) and left ventricular weight (0.467 +/- 0.027 g/100 g body weight) remained unchanged in the group receiving spironolactone, the expression of both types of collagen mRNA and cardiac interstitial and perivascular fibrosis showed a significant decrease compared with the vehicle-treated group. In the rats receiving combined treatment with the ARB and spironolactone, left ventricular weight (0.352 +/- 0.005 g/100 g body weight, P < 0.05), expression of collagen mRNA, and cardiac interstitial and perivascular fibrosis all showed a further improvement compared with both the ARB and spironolactone groups.

CONCLUSIONS

These results demonstrate that residual aldosterone has a significant impact on target-organ damage in hypertension, even during chronic administration of an ARB. The addition of an aldosterone antagonist has an advantage in facilitating the cardioprotective effects of ARBs.

A comparison of the potassium and magnesium-sparing properties of amiloride and spironolactone in diuretic-treated normal subjects

1. The relative potencies of amiloride (5 and 20 mg) and spironolactone (25 and 100 mg) for plasma and erythrocyte electrolytes were investigated in a double-blind, randomised, balanced, crossover study in 12 normal men treated concomitantly with hydrochlorothiazide 100 mg daily for 1 week. 2. Participants satisfied an a priori requirement for a fall in plasma potassium concentration of at least 0.5 mmol l-1 after 7 days of treatment with hydrochlorothiazide alone. 3. After hydrochlorothiazide alone, plasma potassium and sodium concentrations fell (P < 0.001). There were associated reductions in erythrocyte sodium (P < 0.01). Plasma magnesium concentration did not change, although erythrocyte magnesium decreased (P < 0.001). 4. Both amiloride and spironolactone attenuated the thiazide-induced fall in plasma potassium (relative potency, amiloride:spironolactone 10:1, 95% confidence interval 6.3-16.2:1). Amiloride but not spironolactone was associated with a dose-related increase in plasma magnesium; a relative potency estimation was precluded. There was little evidence of influences of amiloride or spironolactone on erythrocyte electrolytes. 5. On a weight basis, amiloride is ten times more potent than spironolactone as a potassium-sparing agent in diuretic-treated subjects but neither agent had major effects on erythrocyte potassium. The drugs may have divergent actions on magnesium handling; hydrochlorothiazide alone had no influence on plasma magnesium.

Adequacy of twice daily dosing with potassium chloride and spironolactone in thiazide treated hypertensive patients

1. The effects of 4-6 weeks treatment with placebo, potassium chloride 32 mmol 12 hourly, and spironolactone 25 mg 12 hourly upon the plasma potassium concentration-time profile were examined in hypertensive patients taking bendrofluazide 5 mg daily. 2. When compared with placebo, potassium chloride increased peak plasma potassium concentration (P less than 0.05), 12 h AUC for plasma potassium (P less than 0.1), and 12 h urine potassium excretion (P = 0.002). Spironolactone increased peak plasma potassium concentration (P less than 0.05), and 12 h AUC for plasma potassium (P less than 0.05), compared with placebo values. 3. Potassium chloride and spironolactone did not differ significantly in any respect other than 12 h urine potassium excretion. The 12 h AUC for plasma potassium was 35% larger with spironolactone than potassium chloride (not significant). 4. With both active drugs peak plasma potassium was observed 2-3 h after dosing, and efficacy tended to wane towards 12 h. However, variability of plasma potassium within the dose interval was not increased markedly, and 12 hourly dosing is probably satisfactory for both potassium chloride and spironolactone at the doses studied.

Hypokalemic and ECG sequelae of combined beta-agonist/diuretic therapy. Protection by conventional doses of spironolactone but not triamterene

Salbutamol (Albuterol) and diuretics are commonly prescribed together in patients with airflow obstruction and are associated with electrocardiographic effects. We have now investigated whether the use of potassium-sparing drugs might prevent the ECG sequelae of such combined therapy. Ten healthy subjects received seven days of randomized treatments with: placebo, bendrofluazide (5 mg), bendrofluazide plus triamterene 50 mg (conventional dose), or triamterene 200 mg (high dose), and bendrofluazide plus spironolactone (100 mg). Potassium and ECG responses to inhaled salbutamol, 2 mg, were measured after each treatment period. The T-wave flattening in response to bendrofluazide and salbutamol (0.24[CI, 0.19 to 0.29]mV) was attenuated by the addition of triamterene, 200 mg (0.33[CI, 0.28 to 0.37]mV; p less than 0.05) and spironolactone 100 mg (0.42[CI, 0.37 to 0.47]mV; p less than 0.01), but not by triamterene 50 mg (0.25[CI, 0.20 to 0.30]mV). Spironolactone and high dose triamterene also diminished the frequency of U waves and ST depression. The ECG effects mirrored hypokalemic responses which were also blunted by high dose (p less than 0.01) but not low dose triamterene, as well as by spironolactone (p less than 0.001). Thus, the use of high dose triamterene and spironolactone protected against the hypokalemic and ECG sequelae of combined beta-agonist/diuretic therapy, whereas a conventional dose of triamterene had no effect. These findings may be important in the prevention of a potentially dangerous interaction in susceptible patients taking this combination of drugs.

Interaction of diuretics and electrolytes in congestive heart failure

Diuretic drugs have been the mainstay of treatment for heart failure. Specific elucidation of the effects of diuretics on electrolytes, however, has been difficult, since the heart failure state itself may alter the electrolyte balance. Nevertheless, it is noteworthy that the natriuretic effect of loop diuretics is greater in edematous patients than in healthy volunteers; yet, the initial kaliuresis is minimal--perhaps because aldosterone levels are low. With continued treatment (or after the edema has been cleared), however, the natriuretic action of loop diuretics is less than that seen in controls, but loss of potassium occurs. The addition of a thiazide to a loop diuretic enhances its natriuretic effect. Both loop and thiazide diuretics can induce depletion of magnesium. Potassium-sparing diuretic drugs augment the natriuresis induced by loop or thiazide diuretics but limit or prevent the loss of potassium or magnesium in the urine, at least in the short term. However, potassium-sparing diuretics can exacerbate the development of hyponatremia.

Spironolactone: a re-examination

A review of the aldosterone antagonist spironolactone is presented. It is effective both as monotherapy and in combination with other hypotensive agents in the control of both essential and hyperaldosterone-induced hypertension. It is useful as a diuretic in conditions such as cirrhosis and congestive heart failure, and is most commonly employed because of its potassium- and magnesium-sparing qualities. Spironolactone also has been used as an antiandrogenic agent in managing hirsutism. Its adverse effect profile, considered somewhat prohibitive in the past, is generally not significant when reasonably low doses (less than 150 mg/d) are used.

Progressive hypokalaemia in elderly patients taking three thiazide potassium-sparing diuretic combinations for thirty-six months

Three different thiazide potassium-sparing diuretic combinations were given to elderly patients for heart failure. Eighty patients received their allocated combinations for 3 years and had 6-monthly measurements of plasma potassium. A further 84 were recruited for study but 29 died within 6 months and 55 had to be withdrawn from the trial. The triamterene-containing preparation was discontinued most frequently (6/44) because of hypokalaemia (plasma potassium less than 3.0 mmol/l); amiloride (5/44) and spironolactone (1/47). The median fall in plasma potassium over 3 years in those patients not withdrawn because of hypokalaemia was similar in each case (P greater than 0.05) and possibly failed to reach significance because of the withdrawal rate (9%). The trend was for a greater fall in those patients taking triamterene. The spironolactone-containing preparation may be the least unsatisfactory of the three.

The influence of dietary potassium on the renal tubular effect of hydrochlorothiazide in the rat

The influence of dietary potassium on the natriuretic effect of hydrochlorothiazide was investigated in conscious rats which had access to 0.46 M NaCl solution; the intake of saline was used as an index of the natriuresis. Control rats drank very little saline (less than 1 mmol 24 h-1), whereas animals given hydrochlorothiazide in the food (35 mg kg-1 dry weight) increased their saline intake to approximately 10 mmol 24 h-1. In a third group of rats, on a high-potassium diet (360 mmol kg-1 dry weight vs 60 mmol kg-1 dry weight), the same dose of hydrochlorothiazide increased the saline intake to only 2 mmol 24 h-1. In order to investigate the renal mechanisms involved in these effects, animals were anaesthetized and prepared for micropuncture. Collections were made from late surface convolutions of proximal tubules and from early and late regions of distal tubules. Total glomerular filtration rate, single-nephron filtration rate, and the delivery of sodium to the end of the proximal tubule and to the beginning of the distal tubule were similar in the three groups of rats. In rats on a normal diet, hydrochlorothiazide treatment was associated with an increased delivery of sodium to the end of the distal tubule. No such increase was seen in thiazide-treated rats on a high potassium intake. It is concluded that a high potassium intake reduces the natriuretic effect of hydrochlorothiazide as a result of interference with thiazide-induced inhibition of sodium reabsorption in the distal tubule. The effect of potassium does not depend on changes in sodium handling in other nephron segments. The possible roles of aldosterone and distal tubular potassium secretion in mediating this effect are discussed.

Comparison of the antihypertensive efficacy and adverse reactions to two doses of bendrofluazide and hydrochlorothiazide and the effect of potassium supplementation on the hypotensive action of bendrofluazide: substudies of the Medical Research Council's trials of treatment of mild hypertension: Medical Research Council Working Party

As substudies of the Medical Research Council's trials of treatment of mild hypertension and of hypertension in the elderly, two studies were carried out comparing the effects of different doses of two diuretics on blood pressure, concentrations of some biochemical variables, and the incidence of subjective adverse reactions. In one study, in which 484 patients with mild hypertension participated, daily doses of bendrofluazide 5 mg and 10 mg, with and without oral potassium supplements, were compared. In the second, involving 701 elderly patients with hypertension, daily doses of hydrochlorothiazide 25 mg together with amiloride 2.5 mg were compared with hydrochlorothiazide 50 mg together with amiloride 5 mg. The mean (+/- SD) durations of treatment were 35 +/- 17 months in the first study and 10 +/- 7 months in the second. Neither study showed any significant difference in blood pressure response to the two doses of diuretic, whereas biochemical changes and the reported incidence of subjective adverse reactions were dose-related. In the first study, potassium supplementation with potassium chloride 16.8 or 33.6 mmol did not have a significant effect on the fall in serum potassium level, which was only slightly reduced, and did not have any significant effect on the antihypertensive effect of either dose of bendrofluazide.

Effects of combined therapy with amiloride and hydrochlorothiazide on plasma and total body potassium, blood pressure, and the renin-angiotensin-aldosterone system in hypertensive patients

After a run-in period of 8 weeks on a regimen of hydrochlorothiazide (HCT, median dosage 75 mg/day), patients with essential hypertension were randomly allocated to continued hydrochlorothiazide therapy (Group I) or additional treatment with amiloride (Group II, median dosage 15 mg/day, or 5 mg per 25 mg hydrochlorothiazide) for the following 12 weeks. Thereafter all the patients were changed to treatment with a fixed combination tablet containing 5 mg amiloride and 50 mg hydrochlorothiazide (Moduretic), keeping the thiazide dosage unchanged for an additional 12 weeks. In Group I patients there was no change in plasma potassium, total body potassium content or the renin-angiotensin-aldosterone system during the 12 weeks on HCT. When the treatment was changed to Moduretic, significant increases were found of 10% in plasma potassium and 3% in total body potassium content. No important stimulation of the renin-angiotensin-aldosterone system was found. In Group II patients addition of an average of 15 mg amiloride to the hydrochlorothiazide treatment led to significant increases in plasma potassium and total body potassium content of approximately 15% and 4%, respectively. There was also a significant increase in the plasma concentrations of renin, angiotensin II and aldosterone. Reducing the average dose of amiloride to 7.5 mg/day by use of Moduretic did not lead to decrease in plasma potassium or total body potassium content. Plasma concentrations of renin, angiotensin II, and aldosterone were decreased, but the individual changes varied markedly and no significant overall change was found.

Pharmacokinetics of potassium chloride in wax-based and syrup formulations

The effect on plasma potassium of 64 mmol potassium chloride (KCl) in two oral formulations was compared against placebo in five healthy men, and their bioavailability was calculated from urinary data. Mean plasma potassium varied between 4.0-4.6 mmol/l during the placebo phase and mean (s.d.) urinary potassium excretion was 84.4 (18.5) mmol over 36 h. KCl syrup produced a significant change in plasma potassium over 24 h (P less than 0.02) with a marked elevation in the first 3 h after dosing and a mean (s.d.) peak plasma potassium 1.72 (0.52) mmol/l higher than placebo (P less than 0.05). By 36 h an excess of 55.9 (23.9) mmol potassium, equivalent to 87.3% of the stated dose, was excreted in the urine. KCl in wax base had a less consistent effect on plasma potassium (P greater than 0.5) and its effect was no more prolonged. The mean peak increment in plasma potassium was 1.03 (0.42) mmol/l (P less than 0.01) and the total potassium excretion was 50.5 (17.7) mmol higher than placebo values giving a bioavailability of 78.8% calculated from the stated dose.

Thiazide-induced hypokalaemia; prevalence higher in women

In 193 hypertensive patients taking bendrofluazide 5 mg daily, the mean serum potassium concentration was lower in women than in men (3.77 vs 3.99 mmol/l, P less than 0.001) and the prevalence of hypokalaemia (less than 3.5 mmol/l) was higher (25% vs 12%, P less than 0.05). This difference between the sexes was independent of age, body weight, renal function, the use of other antihypertensive drugs and compliance with treatment as judged by tablet counts. Severe hypokalaemia (less than 3.0 mmol/l) was uncommon and showed no difference between the sexes.

Metabolic effects of high dose amiloride and spironolactone: a comparative study in normal subjects

Amiloride (75 mg daily) and spironolactone (300 mg daily) were given to five normal subjects for 7 days in order to compare metabolic effects at maximal doses. Blood pressure, body weight, Na+ and K+ balance, and plasma concentrations of Na+, K+, active and total renin, angiotensin II, aldosterone, 11-deoxycorticosterone (DOC), 18-hydroxydeoxycorticosterone (18-OH DOC), corticosterone (B), 18-hydroxycorticosterone (18-OH B) and cortisol were measured before and on each day of treatment. Natriuresis and K+ retention were significantly greater with amiloride. Plasma K+ increased from 4.1 +/- 0.2 to 4.9 +/- 0.2 mmol/l (mean +/- s.d.) on amiloride and from 4.0 +/- 0.2 to 4.4 +/- 0.2 mmol/l with spironolactone. Stimulation of renin, angiotensin II, aldosterone and 18-OH B occurred with both drugs but was greater with amiloride in each case. A transient decrease in systolic and diastolic blood pressure was observed after 2 days of spironolactone treatment but not with amiloride. The slope of the regression of aldosterone on angiotensin II during spironolactone treatment was less than that with amiloride, consistent with partial blockade of aldosterone synthesis by spironolactone. These data suggest that the maximum metabolic effects of amiloride exceed those of spironolactone.

Relative potency of prorenoate potassium and spironolactone in attenuating diuretic induced hypokalaemia

The plasma potassium responses to the aldosterone antagonists prorenoate K (10 mg/day and 40 mg/day) and spironolactone (25 mg/day and 100 mg/day) were compared following treatment for 11 days in combination with the diuretic metolazone (2.5 mg/day) in a double-blind crossover study in twelve healthy men. The best estimate of the potency of prorenoate K relative to spironolactone in attenuating metolazone induced hypokalaemia was 5.6 with 95% confidence limits 2.4-35.2. The method employed allowed a statistically valid quantitative comparison of the potassium sparing properties of the mineralocorticoid antagonists after repeated doses and may be useful in the preclinical evaluation of these drugs.

Potassium-sparing diuretics: interaction with digoxin in elderly men

The effects of two potassium-sparing diuretic combination drugs, triamterene-hydrochlorothiazide and spironolactone-hydrochlorothiazide, were compared with those of two kaliuretic diuretics, hydrochlorothiazide and furosemide, in order to ascertain the effects of those diuretics on concentrations of serum digoxin, serum potassium, and erythrocyte potassium, and to determine whether any of these diuretics should be preferred for patients taking digoxin. It was concluded that in patients for whom potassium depletion may lead to digoxin toxicity, a potassium-sparing diuretic may safely be used in order to reduce potassium excretion and thereby reduce the risk of arrhythmias.

Studies of impaired aldosterone response to spironolactone-induced renin and potassium elevations in adenomatous but not hyperplastic primary aldosteronism

Spironolactone (SPL) corrects hypertension, hypokalemia, and hyporeninemia in patients with primary hyperaldosteronism (PHA) by blocking mineralocorticoid (MCH) receptors. We evaluated the effect of continuous SPL treatment (100 to 300 mg/day for 7 days to 9 years) on plasma renin (PRC), potassium, aldosterone (PA), 18-hydroxycorticosterone (18-OHB), deoxycorticosterone (DOC), and corticosterone (B) concentrations and 24-hour urinary excretion of aldosterone (UA) in 24 patients with PHA (15 with an aldosterone-producing adenoma [APA] and nine with idiopathic PHA [IHA]). Despite the normalization of PRC and K in both APA and IHA patients by SPL, UA and PA failed to increase in APA (55.8 +/- 8.8 to 51.4 +/- 7.3 micrograms/24 hr and 54.0 +/- 9.4 to 44.6 +/- 6.2 ng/dl, respectively) in contrast to rises in IHA patients (22.3 +/- 2.5 to 69.3 +/- 10.3 micrograms/24 hr and 16.0 +/- 1.0 to 49.9 +/- 9.9 ng/dl). Similar corrections with amiloride (20-40 mg/day for 2 months) in one patient with APA produced a three- to fourfold increase in UA and PA. In addition, while on SPL the characteristic fall or no change in PA and 18-OHB during upright posture persisted in all APA patients despite further increases in PRC (4.48 +/- 1.15 to 7.86 +/- 1.89) and K (4.0 +/- 0.1 to 4.3 +/- 0.1). The patterns of the aldosterone precursors, DOC, B, and 18-OHB, and their ratios to acute stimulation with cosyntropin were not altered by SPL. Thus, SPL treatment causes a sustained impairment of the aldosterone secretory response to normalized PRC and K, but not to ACTH stimulation, only in patients with APA.

Use of a bioassay in healthy men to evaluate diuretic-spironolactone combinations

The plasma potassium responses to 1 week's treatment with metolazone 0.625 mg, 1.25 mg and 2.5 mg in combination with spironolactone 50 mg, and metolazone 2.5 alone were examined in a double-blind, crossover study in twelve healthy subjects. Spironolactone attenuated the hypokalaemia induced by metolazone--addition of spironolactone 50 mg to metolazone 2.5 mg raised plasma potassium by 0.18 mmol/l (P less than 0.025). In the presence of spironolactone, a linear log metolazone dose-plasma potassium response relationship (P less than 0.01) was demonstrated. Spironolactone was unable to compensate fully for metolazone's hypokalaemic effect although in combination with metolazone 0.625 mg and 1.25 mg, plasma potassium concentration was maintained close to pretreatment levels. The human bioassay employed provided conveniently quantitative information which allows the rational development of a fixed dose diuretic-spironolactone combination tablet.

The therapeutic use of a new potassium-sparing diuretic, amiloride, and a converting enzyme inhibitor, MK-421, in preventing hypokalemia associated with primary and secondary hyperaldosteronism

This presentation is a summary of our recent clinical studies on the therapeutic use of a new potassium-sparing diuretic, amiloride, and a converting enzyme inhibitor, MK-421, in preventing hypokalemia associated with primary and secondary hyperaldosteronism. These drugs are quite different in their physiologic action but they both may be effective in preventing the potassium depletion associated with increased aldosterone production. Amiloride, which blocks the sodium channels in distal renal tubular cells, was administered to 10 patients with primary hyperaldosteronism and five patients with Bartter's syndrome (secondary hyperaldosteronism). Amiloride, at doses of 10-40 mg/day, increased mean plasma potassium levels in both primary hyperaldosteronism (3.2-4.5 mEq/L) and, to a lesser extent, in Bartter's syndrome (2.5-3.6 mEq/L). The blood pressure fell slightly but significantly in primary hyperaldosteronism (171/112 vs 150/97 mm Hg) and remained unchanged in Bartter's syndrome (116/80 vs 117/71 mm Hg). The plasma renin activity and plasma aldosterone rose in primary aldosteronism (PRA 0.39-2.21 ng A1/m1/h and PA 28.4-54.3 ng/d1); but in Bartter's syndrome, the PRA declined (25.3-11.9 ng A1/m1/h) and the PA rose (19.5-38.0 ng/d1). The discrepancy in the PRA between primary aldosteronism and Bartter's syndrome may be due to the effects of potassium repletion on suppressing renin and stimulating aldosterone; while in primary aldosteronism, a mild diuretic effect could explain the rise in PRA. In both of these disorders, despite the rise in plasma potassium levels, amiloride produced a counter-therapeutic rise in PA which could potentiate further potassium losses. Therefore, we undertook a study to evaluate the prevention of diuretic-induced hypokalemia and secondary hyperaldosteronism using a new converting enzyme inhibitor, MK-421. Eighteen normal subjects were randomized into three groups receiving either (1) hydrochlorothiazide alone (50 mg/day), (2) MK-421 alone (10 mg/day), or (3) hydrochlorothiazide (50 mg/day) plus MK-421 (10 mg/day). Although MK-421 did not prevent diuretic-induced hypokalemia or hyperaldosteronism in the first week, after that time hypokalemia was reversed and ASR returned to normal. In these studies, it therefore appears that while potassium-sparing diuretics may remain the medical mainstay in treating primary aldosteronism, new converting enzyme inhibitors such as MK-421 may be more effective in treating secondary hyperaldosteronism, since potassium levels can be normalized without increasing aldosterone secretion.

Diuretic induced hypokalaemia: relationship to dosage interval and plasma aldosterone

Plasma potassium and aldosterone responses to 9 days treatment with hydrochlorothiazide (100 mg/day) alone or in combination with spironolactone (100 mg/day), prescribed once daily or in doses 12 h apart, were examined in a double-blind, crossover study in twelve healthy subjects. Plasma potassium concentrations were lower when the drugs were administered 12 h apart (P less than 0.01). Spironolactone attenuated significantly hydrochlorothiazide induced hypokalaemia--mean rise in plasma potassium, 0.36 mmol/l (P less than 0.001). The increase in plasma aldosterone was greater following combination therapies (P less than 0.001), but there were no significant differences between once daily and twice daily regimens. We conclude that plasma potassium concentration is better maintained when diuretics are given once daily and that this is not related closely to differences in plasma aldosterone responses.

Relative potency of spironolactone, triamterene and potassium chloride in thiazide-induced hypokalaemia

1 The influence of spironolactone 50 mg and 100 mg daily, triamterene 100 mg and 200 mg daily, potassium chloride 32 mmol and 64 mmol daily and placebo on plasma potassium and other variables was examined in a random crossover study of nine hypertensive patients taking bendrofluazide 10 mg daily. 2 Spironolactone and triamterene had significant and parallel dose-response curves for plasma potassium, with a relative potency for triamterene:spironolactone of 0.25:1, significantly lower than the accepted 0.5:1 ratio. These drugs also lowered serum sodium, bicarbonate and body weight, and increased serum urea and creatinine. 3 Potassium chloride increased plasma potassium above placebo values, but the dose-response was not significant and was not parallel with those of the potassium-sparing drugs. Seven of nine patients remained hypokalaemic despite treatment with 64 mmol potassium chloride daily. 4 The relative expense, convenience and toxicity of the potassium-sparing drugs should be assessed at equivalent doses, namely spironolactone 50 mg:triamterene 200 mg:amiloride 20 mg. Potassium chloride does not correct moderate diuretic-induced hypokalaemia even at doses of 64 mmol daily.

Amiloride: a molecular probe of sodium transport in tissues and cells

The potassium-sparing diuretic amiloride has proven to be a useful pharmacological tool for elucidating the molecular basis and physiological regulation of facilitated sodium entry in tissues and cells. There are two general classes of Na+ transport mechanisms which are sensitive to this drug: 1) a conductive Na+ entry pathway found in electrically high resistance epithelia and 2) a Na+-H+ electroneutral exchange system found in certain leaky epithelia such as the renal proximal tubule. This latter system is also found in many different cellular preparations and seems to function in cell proliferation and differentiation, volume regulation, and intracellular pH regulation. In these cells, this exchange pathway becomes operational usually after some external stimuli. Much higher concentrations of amiloride are required to inhibit the exchange pathway than those required to inhibit the Na+ entry pathway. This drug is the most potent and specific inhibitor of Na+ entry found to date and thus affords the opportunity to be used as a label for the isolation of these transport moieties.

Potassium conservation with amiloride/hydrochlorothiazide ("Moduret') in thiazide-induced hypokalaemia in hypertension

A double-blind study was carried out in 24 hypertensive patients with thiazide-induced hypokalaemia (serum potassium less than 3.2 mmol/l) to compare the effects of treatment with an amiloride/hydrochlorothiazide combination or hydrochlorothiazide alone. The study was divided into three phases: (i) potassium repletion (Weeks 0 to 4) with oral potassium chloride (40 mmol/day), (ii) stabilization (Weeks 4 to 6) of normokalaemia, and (iii) active drug treatment (Weeks 6 to 14), patients being allocated at random to receive one or other of the two treatments. Dosage was 2 tablets per day of the 5 mg amiloride plus 50 mg hydrochlorothiazide combination or of 50 mg hydrochlorothiazide alone. The results showed that blood pressure control was comparable in both treatment groups but hydrochlorothiazide alone caused a statistically significant reduction in serum potassium levels compared to the drug combination. Apart from 1 patient who developed hypokalaemia on hydrochlorothiazide alone, no other side-effects of treatment were reported.

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.

Spironolactone in thiazide-induced hypokalaemia: variable response between patients

1 The influence of spironolactone 25, 50, 100 and 200 mg daily, and placebo, on plasma potassium and other variables was examined in a random crossover study of 15 hypertensive patients taking bendrofluazide 10 mg daily. 2 Spironolactone produced significant dose-related increases in plasma potassium and aldosterone, and reductions in plasma sodium and bicarbonate. 3 In 14 compliant patients plasma concentrations of the major metabolite canrenone were related linearly to the dose of spironolactone, and there was less than twofold variation between patients. The plasma canrenone concentration correlated negatively with body weight (r = -0.77, P less than 0.001). 4 The plasma potassium response to spironolactone varied sevenfold between compliant patients. The response correlated negatively with placebo plasma potassium (r = -0.62, P less than 0.02), positively with plasma canrenone (r = +0.55, P less than 0.05), but was unrelated to plasma aldosterone (r = -0.22). In one patient relative resistance to spironolactone was attributed to exaggerated secondary hyperaldosteronism induced by the drug. 5 The variability in response to spironolactone between patients is such that fixed dose thiazide-spironolactone combination tablets are unlikely to prevent hypokalaemia reliably.

Diuretic treatment of resistant hypertension

In patients with hypertension resistant to three or four drugs including a thiazide diuretic substitution of frusemide for the thiazide, or the addition of spironolactone, produced significant reductions in blood pressure and body weight. The response did not depend on the presence of overt fluid retention, renal impairment, or the use of antihypertensive drugs of high potency. Women had larger responses than men. Expansion of the plasma or extracellular fluid volume is an important cause of resistance to treatment even when a thiazide diuretic is used. An increase in diuretic treatment should be tried before using the postganglionic adrenergic blockers or minoxidil in resistant hypertension.