**4. Spironolactone**

Spironolactone (Figure 1) was synthesized in the Searle Laboratories in 1958 and its aldosterone blocking activity was discovered in 1959 (Cella et al., 1959). The molecule was approved for clinical use in 1962 and has been used for many decades in the treatment of primary aldosteronism, ascites associated with portal hypertension, and congestive heart failure. It has been used also for the treatment of primary hypertension (De Gasparo et al., 1987).

## **4.1 Metabolism**

Spironolactone is a well-absorbed (approximately 65%), lipid-soluble, and highly protein bound steroidal aldosterone antagonist. It is largely metabolized in a hepatic first-pass with a high degree of enterohepatic cycling and a half-life of 1.6 hours, as such. In fact, spironolactone is transformed to either 7-thiomethylspirolactone or canrenone, two active metabolites that account for much of its pharmacological activity. Canrenone has a 20-hour half-life, but this is prolonged in patients with cardiac insufficiency. Spironolactone is also an inducer of microsomal drug metabolizing enzymes in the liver. The onset of action of spironolactone is slow, with a peak response that is reached approximately 48 hours after the first oral dose. Spironolactone is moderately more potent than eplerenone in blocking mineralocorticoid receptors. Spironolactone remains active when renal function is impaired because it reaches its site of action independent of glomerular filtration. This accounts for the risk of hyperkalemia observed in patients with chronic kidney disease and in patients with congestive heart failure and impaired renal function.

#### **4.2 Dosing**

74 Antihypertensive Drugs

Fig. 4. Effect of aldosterone (A) on blood vessels. Aldosterone binds to mineralocorticoid receptors (MR) increasing generation of reactive oxygen species (ROS) and induces endothelial cell swelling and stiffening via a mineralocorticoid receptor-dependent pathway involving the NADPH oxidase and epithelial sodium channel, respectively. Both effects are blocked by mineralocorticoid receptor antagonists. Increased oxidative stress turns cortisol (C) to be an agonist rather than an antagonist of mineralocorticoid receptor. Aldosterone might exert its deleterious cardiovascular effects also through a mineralocorticoid receptor-independent pathway involving the G protein coupled receptor (GPR30) that can induce vascular smooth muscle cell apoptosis and inappropriate vasoconstriction. The pathophysiological role of these

Spironolactone (Figure 1) was synthesized in the Searle Laboratories in 1958 and its aldosterone blocking activity was discovered in 1959 (Cella et al., 1959). The molecule was approved for clinical use in 1962 and has been used for many decades in the treatment of primary aldosteronism, ascites associated with portal hypertension, and congestive heart failure. It has been used also for the treatment of primary hypertension (De Gasparo et al.,

Spironolactone is a well-absorbed (approximately 65%), lipid-soluble, and highly protein bound steroidal aldosterone antagonist. It is largely metabolized in a hepatic first-pass with a high degree of enterohepatic cycling and a half-life of 1.6 hours, as such. In fact, spironolactone is transformed to either 7-thiomethylspirolactone or canrenone, two active metabolites that account for much of its pharmacological activity. Canrenone has a 20-hour half-life, but this is prolonged in patients with cardiac insufficiency. Spironolactone is also an inducer of microsomal drug metabolizing enzymes in the liver. The onset of action of spironolactone is slow, with a peak response that is reached approximately 48 hours after

"non-genomic" effects of aldosterone needs to be further explored.

**4. Spironolactone** 

1987).

**4.1 Metabolism** 

The recommended oral dosing range of spironolactone is from 12.5 to 250 mg once or twice a day in primary hypertension and other disease conditions in which the use of this agent is indicated.

#### **4.3 Clinical use**

Spironolactone is a medication that has been used for more than 50 years to treat hypertension, edema, primary aldosteronism, and, more recent evidence indicates benefits also in patients with congestive heart failure and proteinuria.

Almost a decade ago, a landmark trial investigated the effects of spironolactone in patients with functional class III-IV systolic heart failure, showing a significant decrease in the mortality rate as compared to patients who received placebo on top of conventional treatment. The Randomized Aldactone Evaluation Study (RALES) (Pitt et al., 1999) was conducted in patients with New York Heart Association (NYHA) class III-IV heart failure who were treated with spironolactone. More recently, it has been suggested that the benefits of spironolactone in the context of cardiac failure are not restricted to patients with impaired systolic function and some studies have tested the effects of spironolactone in patients with heart failure and preserved systolic function (HFPSF). Edwards et al. reported improved diastolic function parameters with use of spironolactone in 112 patients with stage 2-3 chronic renal failure and HFPSF who were included in the Chronic Renal Impairment in Birmingham (CRIB II) study. In this study, the effects of spironolactone on left ventricular function and circulating markers of collagen turnover were compared with those of placebo. After 40 weeks, spironolactone improved significantly markers of left ventricular relaxation and attenuated significantly the increase in aminoterminal propeptide of type-III procollagen that was observed with placebo. This and other studies on HFPSF suggest a possible benefit of spironolactone also on this subtype of cardiac insufficiency. Notably, all these studies have employed doses of spironolactone (from 25 to 50 mg/day) that did not lower blood pressure suggesting that the cardioprotective effects of spironolactone occurs independent of the blood pressure-related hemodynamic load to the heart. Taken together, the findings obtained in the studies that have tested the effects of spironolactone in heart failure provide indirect evidence of untoward effect of aldosterone on the heart.

Many studies have reported a beneficial effect of blockers of the renin-angiotensinaldosterone system in slowing down progression of renal disease, but the relative contributions of angiotensin II versus aldosterone have been dissociated only recently in animal studies. Clinical studies have supported the view that mineralocorticoid receptor blockade may exert an antialbuminuric effect in patients with proteinuria. In patients with diabetic nephropathy, it was shown that the antiproteinuric effect of angiotensin-converting enzyme (ACE) inhibitors reverts to baseline in patients who manifest aldosterone escape

Potassium-Sparing Diuretics in Hypertension 77

Several clinical case reports suggested that spironolactone can be useful in the treatment of resistant hypertension and, in particular, in hypertension associated to obesity or obstructive sleep apnea syndrome. One controlled and several non-controlled studies have confirmed that addition of 25-50 mg of spironolactone to current treatment effectively reduces blood pressure in patients with resistant hypertension. In the ASPIRANT trial, 117 patients with resistant hypertension were randomized to treatment with spironolactone or placebo in a double-blind protocol. The trial was prematurely stopped after the first interim analysis because of a significant reduction of systolic blood pressure in patients taking spironolactone as compared to those taking placebo. Notably, the average BMI of the study population in this trial was 32.3 clearly indicating that patients were either obese or overweight. In the prospective, uncontrolled study of Souza et al., 175 patients with resistant hypertension were treated with 25-100 mg/day of spironolactone and, after a median interval of 7 months, 24-hour systolic and diastolic blood pressure decreased by 16 mm Hg and 9 mm Hg, respectively. The baseline characteristics of these patients showed again that they were either overweight or obese and had high prevalence of diabetes, dyslipidemia, left ventricular hypertrophy, and previous cardiovascular diseases. In the ASCOT-BPLA trial, patients who took spironolactone as fourth line therapy because of resistant hypertension were analyzed retrospectively. In these patients, spironolactone at a median dose of 25 mg/day significantly reduced blood pressure by 21.9/9.5 mm. Even in this study, patients with resistant hypertension had significantly higher body mass index, systolic blood pressure, and prevalence of diabetes and left ventricular hypertrophy than patients who were not resistant to treatment. Very similar results were reported in other studies

The beneficial effect of spironolactone in patients with resistant hypertension is currently unexplained, although this effect suggests a substantial contribution of aldosterone to maintenance of increased blood pressure despite of treatment. Inappropriate secretion of aldosterone has been reported in hypertensive patients with associated obesity and/or obstructive sleep apnea syndrome. Also, it is well known that aldosterone can escape the inhibitory effects of renin-angiotensin system blockers in patients treated with these drugs, thereby leading to a form of hypertension that is largely aldosterone-dependent. Finally, it cannot be excluded that, at least in some cases, resistance to antihypertensive treatment

Spironolactone is the drug of choice in the medical treatment of primary aldosteronism in which hypertension is due to an excessive aldosterone secretion from the adrenal gland. In this clinical setting, spironolactone reduces blood pressure, corrects hypokalemia, and reverts cardiac and renal abnormalities as it has been reviewed recently. This was demonstrated in long-term follow-up studies in which treatment with spironolactone reduced cardiovascular and renal events and decreased left ventricular mass and urinary

Cardiovascular outcomes were compared in 108 patients with essential hypertension and in 54 patients with primary aldosteronism who were comparable for demographic variables and had comparable risk factors, but greater retrospective incidence of coronary artery

protein excretion in patients with primary aldosteronism (Sechi et al., 2010).

**4.3.2 Resistant hypertension** 

conducted on patients of different geographical areas.

hides a mild form of primary aldosteronism.

**4.3.3 Primary aldosteronism** 

and that spironolactone combined with an ACE inhibitor results in an additional decrease in albuminuria (Sato et al., 2003). Also, spironolactone effectively reduced proteinuria in patients with idiopathic chronic glomerulonephritis previously treated with either ACE inhibitors or angiotensin receptor blockers (Bianchi et al., 2005). Another, more recent, study has shown that spironolactone added to an ACE inhibitor or an angiotensin receptor blocker reduces albuminuria in patients with type 2 diabetes and nephropathy. Collectively, these observations suggest that the mechanisms of the antialbuminuric effect of spironolactone are independent of blood pressure reduction and occur on top of those of other blockers of the renin-angiotensin system.

#### **4.3.1 Essential hypertension**

The anti-hypertensive effects of spironolactone have been overviewed in a recent metaanalysis that has included five cross-over studies and one randomized controlled trial with a total of 179 essential hypertensive patients that were followed from 4 to 8 weeks (Batterink et al., 2010). This meta-analysis showed that spironolactone decreases systolic and diastolic blood pressure by 20 and 7 mmHg, respectively, but this effect is reached with doses between 100 and 500 mg per day. With these doses, the risk of hyperkalemia is an important limitation and this is why use of spironolactone in the treatment of essential hypertension has been limited to combination with other types of diuretics. The dose of 25 mg/day did not change either systolic or diastolic blood pressure. None of the studies that were included in this meta-analysis reported results for hard endpoints such as mortality and major cardiovascular events. Therefore, at present there is no evidence that use of spironolactone decreases the risk of cardiovascular disease.

Despite the effects of spironolactone on blood pressure in essential hypertensive patients are modest and there is no demonstration that spironolactone protects from cardiovascular events, possible benefits on subclinical hypertensive organ damage that might be obtained even with the lower doses of the drug should be considered. Some small studies conducted in patients with hypertension-induced left ventricular hypertrophy have reported that addition of spironolactone to blockers of the renin-angiotensin system increases the effects on left ventricular mass reduction. The effects of an ACE-inhibitor alone or an ACE-inhibitor plus spironolactone (25 mg/day) on blood pressure and left ventricular mass changes were compared in essential hypertensive patients with left ventricular hypertrophy. Left ventricular mass index decreased in both treatment groups, but the extent of reduction was significantly greater in patients who were treated with the combination of the ACE-inhibitor and spironolactone. Similarly, the effects of candesartan (8 mg/day) alone or combined with spironolactone (25 mg/day) were tested in patients with hypertension and different patterns of left ventricular geometry. Changes in blood pressure did not differ between the two groups, whereas only the combination of candesartan and spironolactone decreased left ventricular mass with a change that was significant only in patients with concentric hypertrophy. In another study, 30 hypertensive patients with impaired diastolic function were randomized to receive either 25 mg/day of spironolactone or placebo for 6 months. Peak systolic strain and cyclic variation of integrated backscatter were improved by spironolactone with significant differences with patients treated with placebo. Thus, current evidence indicates that spironolactone could have a considerable place in the treatment of essential hypertensive patients with left ventricular hypertrophy and/or diastolic dysfunction.

#### **4.3.2 Resistant hypertension**

76 Antihypertensive Drugs

and that spironolactone combined with an ACE inhibitor results in an additional decrease in albuminuria (Sato et al., 2003). Also, spironolactone effectively reduced proteinuria in patients with idiopathic chronic glomerulonephritis previously treated with either ACE inhibitors or angiotensin receptor blockers (Bianchi et al., 2005). Another, more recent, study has shown that spironolactone added to an ACE inhibitor or an angiotensin receptor blocker reduces albuminuria in patients with type 2 diabetes and nephropathy. Collectively, these observations suggest that the mechanisms of the antialbuminuric effect of spironolactone are independent of blood pressure reduction and occur on top of those of other blockers of

The anti-hypertensive effects of spironolactone have been overviewed in a recent metaanalysis that has included five cross-over studies and one randomized controlled trial with a total of 179 essential hypertensive patients that were followed from 4 to 8 weeks (Batterink et al., 2010). This meta-analysis showed that spironolactone decreases systolic and diastolic blood pressure by 20 and 7 mmHg, respectively, but this effect is reached with doses between 100 and 500 mg per day. With these doses, the risk of hyperkalemia is an important limitation and this is why use of spironolactone in the treatment of essential hypertension has been limited to combination with other types of diuretics. The dose of 25 mg/day did not change either systolic or diastolic blood pressure. None of the studies that were included in this meta-analysis reported results for hard endpoints such as mortality and major cardiovascular events. Therefore, at present there is no evidence that use of spironolactone

Despite the effects of spironolactone on blood pressure in essential hypertensive patients are modest and there is no demonstration that spironolactone protects from cardiovascular events, possible benefits on subclinical hypertensive organ damage that might be obtained even with the lower doses of the drug should be considered. Some small studies conducted in patients with hypertension-induced left ventricular hypertrophy have reported that addition of spironolactone to blockers of the renin-angiotensin system increases the effects on left ventricular mass reduction. The effects of an ACE-inhibitor alone or an ACE-inhibitor plus spironolactone (25 mg/day) on blood pressure and left ventricular mass changes were compared in essential hypertensive patients with left ventricular hypertrophy. Left ventricular mass index decreased in both treatment groups, but the extent of reduction was significantly greater in patients who were treated with the combination of the ACE-inhibitor and spironolactone. Similarly, the effects of candesartan (8 mg/day) alone or combined with spironolactone (25 mg/day) were tested in patients with hypertension and different patterns of left ventricular geometry. Changes in blood pressure did not differ between the two groups, whereas only the combination of candesartan and spironolactone decreased left ventricular mass with a change that was significant only in patients with concentric hypertrophy. In another study, 30 hypertensive patients with impaired diastolic function were randomized to receive either 25 mg/day of spironolactone or placebo for 6 months. Peak systolic strain and cyclic variation of integrated backscatter were improved by spironolactone with significant differences with patients treated with placebo. Thus, current evidence indicates that spironolactone could have a considerable place in the treatment of essential

hypertensive patients with left ventricular hypertrophy and/or diastolic dysfunction.

the renin-angiotensin system.

**4.3.1 Essential hypertension** 

decreases the risk of cardiovascular disease.

Several clinical case reports suggested that spironolactone can be useful in the treatment of resistant hypertension and, in particular, in hypertension associated to obesity or obstructive sleep apnea syndrome. One controlled and several non-controlled studies have confirmed that addition of 25-50 mg of spironolactone to current treatment effectively reduces blood pressure in patients with resistant hypertension. In the ASPIRANT trial, 117 patients with resistant hypertension were randomized to treatment with spironolactone or placebo in a double-blind protocol. The trial was prematurely stopped after the first interim analysis because of a significant reduction of systolic blood pressure in patients taking spironolactone as compared to those taking placebo. Notably, the average BMI of the study population in this trial was 32.3 clearly indicating that patients were either obese or overweight. In the prospective, uncontrolled study of Souza et al., 175 patients with resistant hypertension were treated with 25-100 mg/day of spironolactone and, after a median interval of 7 months, 24-hour systolic and diastolic blood pressure decreased by 16 mm Hg and 9 mm Hg, respectively. The baseline characteristics of these patients showed again that they were either overweight or obese and had high prevalence of diabetes, dyslipidemia, left ventricular hypertrophy, and previous cardiovascular diseases. In the ASCOT-BPLA trial, patients who took spironolactone as fourth line therapy because of resistant hypertension were analyzed retrospectively. In these patients, spironolactone at a median dose of 25 mg/day significantly reduced blood pressure by 21.9/9.5 mm. Even in this study, patients with resistant hypertension had significantly higher body mass index, systolic blood pressure, and prevalence of diabetes and left ventricular hypertrophy than patients who were not resistant to treatment. Very similar results were reported in other studies conducted on patients of different geographical areas.

The beneficial effect of spironolactone in patients with resistant hypertension is currently unexplained, although this effect suggests a substantial contribution of aldosterone to maintenance of increased blood pressure despite of treatment. Inappropriate secretion of aldosterone has been reported in hypertensive patients with associated obesity and/or obstructive sleep apnea syndrome. Also, it is well known that aldosterone can escape the inhibitory effects of renin-angiotensin system blockers in patients treated with these drugs, thereby leading to a form of hypertension that is largely aldosterone-dependent. Finally, it cannot be excluded that, at least in some cases, resistance to antihypertensive treatment hides a mild form of primary aldosteronism.

#### **4.3.3 Primary aldosteronism**

Spironolactone is the drug of choice in the medical treatment of primary aldosteronism in which hypertension is due to an excessive aldosterone secretion from the adrenal gland. In this clinical setting, spironolactone reduces blood pressure, corrects hypokalemia, and reverts cardiac and renal abnormalities as it has been reviewed recently. This was demonstrated in long-term follow-up studies in which treatment with spironolactone reduced cardiovascular and renal events and decreased left ventricular mass and urinary protein excretion in patients with primary aldosteronism (Sechi et al., 2010).

Cardiovascular outcomes were compared in 108 patients with essential hypertension and in 54 patients with primary aldosteronism who were comparable for demographic variables and had comparable risk factors, but greater retrospective incidence of coronary artery

Potassium-Sparing Diuretics in Hypertension 79

Ciba-Geigy laboratories in the mid-80s and was approved in the United States for clinical

Eplerenone was synthesized by replacing the 17-thioacetyl group with a carbomethoxy group in the molecule of spironolactone (Figure 1). The critical feature in the eplerenone molecule however, conferring enhanced mineralocorticoid receptor selectivity is the presence of the epoxide group in the lactone ring. The activity of eplerenone in vitro was assessed in vitro using recombinant steroid receptors. The potency of eplerenone at other steroid receptors was significantly reduced and, unlike previous aldosterone blockers, eplerenone possesses

Oral bioavailability is approximately 95% and meals have no effect on the extent of absorption. Eplerenone does not undergo relevant metabolic first-pass in the liver neither it induces cytochrome P450 activity, although interactions with drugs that are metabolized by cytochrome P450 are not excluded. The two main metabolites of eplerenone (6β-OH eplerenone and open lactone ring) are both mineralocorticoid receptor-inactive. The plasma

The recommended oral dosing range for eplerenone is from 50 to 100 mg once or twice daily in essential hypertension. No correlations between eplerenone disposal and renal function

Eplerenone has come into the clinical arena in the last decade and has been employed to lower blood pressure in essential hypertensive patients. Similar to spironolactone, recent studies have reported beneficial effects of eplerenone in congestive heart failure and renal disease with proteinuria. The Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival Study (EPHESUS) (Pitt et al. 2003) investigated the effects of eplerenone in postmyocardial infarction patients with severely impaired left ventricular function, showing a significant decrease in the mortality rate as compared to patients who received placebo on top of conventional treatment. Recently, these observations have been extended to patients with milder degrees of cardiac dysfunction in the Eplerenone in Mild Patients Hospitalization and Survival Study in Heart Failure (EMPHASIS-HF) (Zannad et al., 2011) study. In this study, 2737 patients with NYHA class II cardiac insufficiency and left ventricular ejection fraction of less than 35% were randomized to receive either eplerenone or placebo in addition to conventional treatment. This trial ended prematurely after a median follow-up of 21 months because the composite endpoint of cardiovascular death and hospitalization for heart failure were significantly less frequent in patients who were treated with eplerenone. Thus,

eplerenone seems to be beneficial even at the early stages of systolic cardiac failure.

As for spironolactone, the possibility that eplerenone may result beneficial also in patients with HFPSF has been investigated. Forty-four elderly patients with heart failure and left ventricular ejection fraction of more than 45% were randomized to conventional treatment with or without eplerenone and left ventricular function was reassessed with conventional echocardiography and tissue Doppler imaging at 6 and 12 months. In patients who were treated with eplerenone, deceleration time had a significantly greater decrease than in

very low activity on the androgen, progesterone, and glucocorticoid receptors.

use in arterial hypertension in 2002.

half-life of eplerenone is approximately 5 hours.

**6.1 Pharmacology** 

have been found.

**6.2 Clinical use** 

disease, cerebrovascular events, and sustained arrhythmias (Catena et al. 2008). Patients were followed for an average of 7.4 years after surgical removal of an adrenal adenoma or treatment with spironolactone, with a combined end point including myocardial infarction, stroke, any type of revascularization procedure, and sustained arrhythmias. During followup, blood pressure was comparable in the primary aldosteronism and essential hypertension group, and 10 patients in the former group and 19 in the latter group reached the end point. Actuarial analysis of patients treated with surgery vs. spironolactone did not reveal significant difference in the occurrence of the combined end point. In the same cohort of patients, the outcomes of renal function were investigated by measuring the rates of change of glomerular filtration and albuminuria (Sechi et al., 2006). After an initial decline in creatinine clearance, due to correction of the aldosterone-induced intrarenal hemodynamic adaptation, subsequent decrease of glomerular filtration in patients with primary aldosteronism and essential hypertension were comparable. Urinary albumin losses did not differ between patients with primary aldosteronism and essential hypertension during follow-up. Evaluation of renal outcomes in patients with primary aldosteronism who were treated with surgery or spironolactone did not reveal significant difference. These two studies clearly demonstrate that spironolactone has the same therapeutic value as surgery in the treatment of primary aldosteronism and in the prevention of cardiovascular and renal complications.

In addition to excess cardiovascular and renal events as compared to matched patients with essential hypertension, patients with primary aldosteronism are characterized by cardiac, renal, and metabolic subclinical structural and functional abnormalities (Rossi et al., 2008). A number of cross-sectional cardiac ultrasound studies have reported an excess increase of left ventricular mass in patients with primary aldosteronism as compared to other types of hypertensive disease. In a 7-year echocardiographic study it was demonstrated that patients with primary aldosteronism treated with either surgery or spironolactone have significant and comparable decrease of left ventricular mass, although decrease is significant within the first year only after adrenalectomy (Catena et al., 2007). We have already mentioned the effects of spironolactone on correction of albuminuria. These effects are at least in part related to reversal of an intrarenal hemodynamic adaptation to aldosterone excess with a vasodilatory response that has been demonstrated with intrarenal echo-Doppler examination (Sechi et al., 2009).
