Comparison of thiazides and amiloride in treatment of moderate hypertension

Amiloride: A review

Amiloride is a potassium retaining diuretic and natriuretic which acts by reversibly blocking luminal epithelial sodium channels (ENaCs) in the late distal tubule and collecting duct. Amiloride is indicated in oedematous states, and for potassium conservation adjunctive to thiazide or loop diuretics for hypertension, congestive heart failure and hepatic cirrhosis with ascites. Historical studies on its use in hypertension were poorly controlled and there is insufficient data on dose-response. It is clearly highly effective in combination with thiazide diuretics where it counteracts the adverse metabolic effects of the thiazides and its use in the Medical Research Council Trial of Older Hypertensive Patients, demonstrated convincing outcome benefits on stroke and coronary events. Recently it has been shown to be as effective as spironolactone in resistant hypertension but there is a real need to establish its potential role in the much larger number of patients with mild to moderate hypertension in whom there is a paucity of information with amiloride particularly across an extended dose range.

Effect of amiloride, or amiloride plus hydrochlorothiazide, versus hydrochlorothiazide on glucose tolerance and blood pressure (PATHWAY-3): a parallel-group, double-blind randomised phase 4 trial

BACKGROUND

Potassium depletion by thiazide diuretics is associated with a rise in blood glucose. We assessed whether addition or substitution of a potassium-sparing diuretic, amiloride, to treatment with a thiazide can prevent glucose intolerance and improve blood pressure control.

METHODS

We did a parallel-group, randomised, double-blind trial in 11 secondary and two primary care sites in the UK. Eligible patients were aged 18-80 years; had clinic systolic blood pressure of 140 mm Hg or higher and home systolic blood pressure of 130 mmHg or higher on permitted background drugs of angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, β blockers, calcium-channel blockers, or direct renin inhibitors (previously untreated patients were also eligible in specific circumstances); and had at least one component of the metabolic syndrome in addition to hypertension. Patients with known diabetes were excluded. Patients were randomly assigned (1:1:1) to 24 weeks of daily oral treatment with starting doses of 10 mg amiloride, 25 mg hydrochlorothiazide, or 5 mg amiloride plus 12·5 mg hydrochlorothiazide; all doses were doubled after 12 weeks. Random assignment was done via a central computer system. Both participants and investigators were masked to assignment. Our hierarchical primary endpoints, assessed on a modified intention-to-treat basis at 12 and 24 weeks, were the differences from baseline in blood glucose measured 2 h after a 75 g oral glucose tolerance test (OGTT), compared first between the hydrochlorothiazide and amiloride groups, and then between the hydrochlorothiazide and combination groups. A key secondary endpoint was change in home systolic blood pressure at 12 and 24 weeks. This trial is registered with ClinicalTrials.gov, number NCT00797862, and the MHRA, Eudract number 2009-010068-41, and is now complete.

FINDINGS

Between Nov 18, 2009, and Dec 15, 2014, 145 patients were randomly assigned to amiloride, 146 to hydrochlorothiazide, and 150 to the combination group. 132 participants in the amiloride group, 134 in the hydrochlorothiazide group, and 133 in the combination group were included in the modified intention-to-treat analysis. 2 h glucose concentrations after OGTT, averaged at 12 and 24 weeks, were significantly lower in the amiloride group than in the hydrochlorothiazide group (mean difference -0·55 mmol/L [95% CI -0·96 to -0·14]; p=0·0093) and in the combination group than in the hydrochlorothiazide group (-0·42 mmol/L [-0·84 to -0·004]; p=0·048). The mean reduction in home systolic blood pressure during 24 weeks did not differ significantly between the amiloride and hydrochlorothiazide groups, but the fall in blood pressure in the combination group was significantly greater than that in the hydrochlorothiazide group (p=0·0068). Hyperkalaemia was reported in seven (4·8%) patients in the amiloride group and three (2·3%) patients in the combination group; the highest recorded potassium concentration was 5·8 mmol/L in a patient in the amiloride group. 13 serious adverse events occurred but the frequency did not differ significantly between groups.

INTERPRETATION

The combination of amiloride with hydrochlorothiazide, at doses equipotent on blood pressure, prevents glucose intolerance and improves control of blood pressure compared with montherapy with either drug. These findings, together with previous data about morbidity and mortality for the combination, support first-line use of amiloride plus hydrochlorothiazide in hypertensive patients who need treatment with a diuretic.

FUNDING

British Heart Foundation and National Institute for Health Research.

A double-blind, placebo-controlled, crossover trial comparing the effects of amiloride and hydrochlorothiazide on glucose tolerance in patients with essential hypertension

Hypertension guidelines advise limiting the dose of thiazide diuretics and avoiding combination with β-blockade, because of increased risk of diabetes mellitus. We tested whether changes in the 2-hour oral glucose tolerance test could be detected after 4 weeks of treatment with a thiazide and could be avoided by switching to amiloride. Two double-blind, placebo-controlled, crossover studies were performed. In study 1 (41 patients), we found that changes in glucose during a 2-hour oral glucose tolerance test could be detected after 4 weeks of treatment with bendroflumethiazide. In study 2, 37 patients with essential hypertension received, in random order, 4 weeks of once-daily treatment with hydrochlorothiazide (HCTZ) 25 to 50 mg, nebivolol 5 to 10 mg, combination (HCTZ 25-50 mg+nebivolol 5-10 mg), amiloride (10-20 mg), and placebo. Each drug was force titrated at 2 weeks and separated by a 4-week placebo washout. At each visit, we recorded blood pressure and performed a 75-g oral glucose tolerance test. Primary outcome was the difference in glucose (over the 2 hours of the oral glucose tolerance test) between 0 and 4 weeks, when HCTZ and amiloride were compared by repeated-measures analysis. For similar blood pressure reductions, there were opposite changes in glucose between the 2 diuretics (P<0.0001). Nebivolol did not impair glucose tolerance, either alone or in combination. There was a negative correlation between Δpotassium and Δ2-hour glucose (r=-0.28; P<0.0001). In 2 crossover studies, 4 weeks of treatment with a thiazide diuretic impaired glucose tolerance. No impairment was seen with K(+)-sparing diuretic or β(1)-selective blockade. Substitution or addition of amiloride may be the solution to preventing thiazide-induced diabetes mellitus.

Hydrochlorothiazide and potassium chloride in comparison with hydrochlorothiazide and amiloride in the treatment of mild hypertension

A randomized, double-blind, cross-over study comparing 50 mg hydrochlorothiazide plus 5 mg amiloride (HCTZ/A) with 50 mg hydrochlorothiazide plus 26 mmol potassium chloride (HCTZ/K) was conducted in 18 patients with mild essential hypertension (diastolic pressure 90-105 mmHg). The sequence of treatment was: placebo for 2 weeks, one active drug for 3 weeks, placebo for 2 weeks, the other active drug for 3 weeks. The two agents were significantly and equally efficacious in lowering the systolic and diastolic blood pressure. Baseline vs. treatment mean serum potassium levels were 3.82 vs. 3.78 mmol/l for HCTZ/A and 3.82 vs. 3.70 mmol/l for HCTZ/K. The decrease in serum potassium level from baseline was significant for both agents but not significantly different when the two treatment forms were compared. Both treatment forms elevated fasting serum cholesterol and glucose. Serum triglycerides and uric acid rose significantly with HCTZ/K. Amiloride may affect the tubular handling of uric acid causing increased uric acid excretion, thus counteracting thiazide-induced hyperuricemia. During 3 weeks' extension of the main study, 5 patients received HCTZ/A in double the original dose (100 mg/10 mg) and 6 patients received HCTZ/K in double the original dose (100 mg/52 mmol). No further blood pressure reduction was observed on treatment with these doses. The mean serum potassium levels did not decrease further on doubling the HCTZ/A dose, while a significant fall was observed for HCTZ/K (3.60 vs. 3.42 mmol/l) (p less than 0.05, single tailed t-test). Both drug combinations were well tolerated and side-effects were not significantly different from those during placebo administration. This study demonstrates that 50 mg hydrochlorothiazide plus 26 mmol potassium chloride are as effective as 50 mg hydrochlorothiazide plus 5 mg amiloride, both in reducing blood pressure and preventing hypokalaemia in the treatment of essential hypertension. A small extension study indicates that amiloride might be more effective than potassium chloride in preventing hypokalaemia when high doses (100 mg/day) of hydrochlorothiazide are administered.

Thiazides and loop-diuretics therapeutic aspects

Thiazides and compounds with similar models of action exert their most important renal effects on the cortical-diluting segment of the nephron, most likely from the peritubular side. In contrast, the most important site of action of loop-diuretics is the luminal side of the ascending part of the diluting segment. The different sites of action explain the clinically proven efficacious combination of thiazides and loop-diuretics in severe cardiac failure. Most thiazides and loop-diuretics are eliminated via renal tubular secretion, which leads to decreased renal clearance in patients with chronic heart failure (CHF) as their renal blood flow is decreased even if glomerular filtration rate (GFR) is maintained. A rational approach to enhance the effects of loop-diuretics is to combine them with drugs that increase renal blood flow, thereby increasing the rate of delivery of the drug to its site of action. Dilutional hyponatremia is an important complication of treatment with diuretics. An efficacious treatment of that condition seems to be a combination of loop-diuretics and ACE-inhibitors. Thiazides decrease the urinary excretion of calcium, while loop-diuretics have the opposite effect. The possibility of loop-diuretic induced osteopenia cannot be ruled out, which should be considered when choosing between thiazides and loop-diuretics for the treatment of mild to moderate CHF.

The spironolactone, amiloride, losartan, and thiazide (SALT) double-blind crossover trial in patients with low-renin hypertension and elevated aldosterone-renin ratio

BACKGROUND

There is continuing variation in diagnosis and estimated prevalence of primary hyperaldosteronism. The higher estimates encourage search for adrenal adenomas in patients with elevated ratios of plasma aldosterone to renin. However, it is more likely that patients with normal plasma K+ and aldosterone belong to the polygenic spectrum of low-renin hypertension rather than have the same monogenic syndrome as classic Conn's. Our primary hypothesis was that in low-renin patients with normal plasma K+ and aldosterone, a thiazide diuretic, bendroflumethiazide, would be as effective as spironolactone in overcoming the Na+ retention and lowering blood pressure. Secondary objectives were to compare the dose response for each diuretic and to evaluate amiloride as an alternative to spironolactone.

METHODS AND RESULTS

Fifty-seven patients entered and 51 patients completed a placebo-controlled, double-blind, randomized crossover trial. Entry criteria included low plasma renin, normal K+, elevated aldosterone-renin ratio, and a previous systolic blood pressure response to spironolactone of > or = 20 mm Hg. Two doses each of spironolactone and bendroflumethiazide were compared. The crossover also included amiloride and losartan. Outcome measures were blood pressure, plasma renin, and other biochemical markers of diuretic action. Spironolactone 100 mg and bendroflumethiazide 5 mg caused similar falls in systolic blood pressure, whereas bendroflumethiazide 2.5 mg was 5/2 mm Hg less effective in reducing blood pressure than either bendroflumethiazide 5 mg or spironolactone 50 mg (P<0.005). Amiloride 40 mg was as effective as the other diuretics. Biochemical indices of natriuresis showed bendroflumethiazide to be less effective than either spironolactone or amiloride; plasma renin rose 4-fold on spironolactone but only 2-fold on bendroflumethiazide (P=0.003).

CONCLUSIONS

In hypertensive patients with a low plasma renin but normal K+, bendroflumethiazide 5 mg was as effective as spironolactone 100 mg in lowering blood pressure, despite patients being selected for a previous large fall in blood pressure on spironolactone. Because this result differs from that expected in primary hyperaldosteronism, our finding argues against low-renin hypertension including a large, undiagnosed pool of primary hyperaldosteronism. However, spironolactone was the more effective natriuretic agent, suggesting that inappropriate aldosterone release or response may still contribute to the Na+ retention of low-renin hypertension.

Aldosterone deficiency in a patient with idiopathic haemochromatosis

Postural hypotension due to low aldosterone secretion was the presenting feature of idiopathic haemochromatosis in a 35-year-old man. Repeated venesection is beneficial in this disease but it is suggested that aldosterone deficiency be excluded before treatment to avoid depletion of circulating volume.