Plasma potassium levels in hypertensive patients receiving fixed-combination diuretic therapy

Update on management of hypokalemia and goals for the lower potassium level in patients with cardiovascular disease: A review in collaboration with the European Society of Cardiology Working Group on Cardiovascular Pharmacotherapy

Hypokalaemia is common in patients with cardiovascular disease. In this review, we emphasize the importance of tight potassium regulation in patients with cardiovascular disease based on findings from observational studies. To enhance the understanding, we also describe the mechanisms of potassium homeostasis maintenance, the most common causes of hypokalaemia and present strategies for monitoring and management of low potassium levels. We propose elevation of potassium in asymptomatic patients with lower normal concentrations and concurrent cardiovascular disease. These proposals are intended to assist clinicians until more evidence is available.

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.

Potassium supplements or potassium-sparing agents

During diuretic treatment alterations in myocardial cellular excitability due to potassium-induced disturbances of the membrane potential may arise without obvious changes of total body K. This may be explained by coexisting disturbances of the acid/base balance and other ions such as magnesium, two factors which independently influence the transport of potassium across the cell membrane. The consequence may be cardiac arrhythmias, particularly in the presence of digitalis. On the other hand hypokalemia, induced by diuretics, may also be accompanied by a significant depletion of total body K, bringing about more general consequences. It must be considered essential to maintain a normal general electrolyte balance during diuretic therapy. Potassium supplements may be used if true depletion of total body K is suspected, e.g. in hypokalemia with acidosis. Its use may, however, otherwise be questioned, as it is only directed towards the potassium situation and neglects the influence of diuretics upon other ions, such as H+ and Mg++. The potassium-sparing agents amiloride and triamterene normalize the general electrolyte situation in the distal tubules and should thus be regarded as drugs of first choice. Spironolactone has identical properties concerning the electrolytes but more serious side effects. It should be preferred when a significant secondary hyperaldosteronism is suspected and/or a more intense diuresis or an accentuated antihypertensive action is desired. The role of captopril in this context has not yet been established.

Combination therapy as first-line treatment for hypertension

With the cut-off point between "normal" and "high" blood pressure (BP) being pushed increasingly downward, especially for patients with multiple cardiovascular risk factors, most hypertensives need more than one antihypertensive agent to reach their target BP. In this article, we examine the rationale for combining drugs from different classes that have synergistic or additive effects and properties that might offset one another's adverse hemodynamic and/or metabolic reactions. We suggest circumstances in which the initiation of therapy with a fixed two-drug combination might be preferable to the usual practice of starting with monotherapy followed by upward titration and addition of other agents, and we briefly review the existing fixed drug combinations. We end with the intriguing and provocative notion of the future "polypill," a fixed combination of agents addressing various components of the metabolic syndrome as well as other coexisting common risk factors in both high-risk patients with conditions requiring polypharmacy and in healthy, asymptomatic individuals.

Renal excretory actions of antihypertensive agents. Effects of rilmenidine

The acute renal excretory actions of several antihypertensive agents were assessed in healthy volunteers. Rilmenidine (1 mg) did not affect water and electrolyte balance. Beta-adrenergic blockers had little effect upon urinary composition, whereas diuretics caused significant urinary losses of fluid, sodium, potassium, and magnesium as expected. The vasodilators ketanserin and flosequinan did not affect water and electrolyte excretion. Ketanserin increased urate output in common with angiotensin-converting enzyme inhibitors, which may act as facultative diuretics. Combining the angiotensin-converting enzyme inhibitor captopril (100 mg) or rilmenidine (1 mg) with hydrochlorothiazide (25 mg) had little influence upon the known actions of the diuretic. When the beta-blocker pindolol (10 mg) was given with the diuretic clopamide (5 mg), beneficial effects were noted; potassium and magnesium losses were markedly reduced, whereas the natriuretic and diuretic effects of clopamide were unchanged. These short-term studies in healthy volunteers provide useful pointers to some possible pharmacodynamic effects of antihypertensive drugs in patients.

Plasma electrolytes in elderly patients taking fixed combination diuretics

Plasma potassium and sodium concentrations were measured in a group of elderly patients taking maintenance thiazide diuretic therapy alone, with a potassium supplement or in combination with a potassium sparing diuretic. Fixed dose combinations of a thiazide and potassium sparing diuretic did not significantly reduce the prevalence of hypokalaemia and the combination of amiloride-hydrochlorothiazide was associated with a disproportionate number of cases of hyponatraemia. The desirability of the current widespread use of fixed dose combination diuretics over less expensive single agents is questioned.

Initial therapy for mild hypertension

The treatment of mild hypertension has been a subject of controversy because its benefits versus risks are not as well established as they are for moderate to severe hypertension. Results of several studies, however, now show that treatment reduces the frequency of stroke in those with milder blood pressure elevations. New guidelines published by the Joint National Committee recommend that treatment of mild hypertension begin with either a diuretic or a beta blocker. The effect on the most common complication of mild hypertension, that is, coronary heart disease (myocardial infarction and sudden cardiac death), has, however, not been encouraging in studies in which diuretics have been used as first-line treatment. Two large-scale primary preventive studies compared the efficacy of diuretics and beta blockers in reducing coronary heart disease in hypertensive patients; results were in favor of beta blocker regimens in men. So far there is some evidence, but no hard scientific proof, that certain beta blockers offer advantages over diuretics in preventing myocardial infarction and sudden cardiac death in hypertensive patients. A major concern with the use of diuretics is the risk of hypokalemia; this can be reduced when they are combined with beta blockers.

Single and divided daily dose piretanide in the treatment of uncomplicated essential hypertension: a double-blind comparison with a combination of hydrochlorothiazide and amiloride

In a randomised double blind study in patients with mild to moderate hypertension, piretanide 6 mg once and twice daily significantly reduced both supine and erect blood pressure. This was seen after only 2 weeks and a further progressive reduction was evident over the ensuing 12-week trial period. The higher dose produced a mean maximal fall of 29% in supine diastolic pressure, compared with 23% after the lower dose; the difference is not significant. Hydrochlorothiazide 50 mg/amiloride 5 mg twice daily (HCT/A) also reduced supine blood pressure significantly after 2 weeks, but the reduction in erect diastolic blood pressure did not achieve statistical significance until 8 weeks. The maximal effect (a 13% fall in supine diastolic blood pressure) was significantly less than that of either piretanide regimen. Blood pressures in this group also returned more rapidly to pretreatment levels during the placebo washout phase at the end of the study. HCT/A produced a significant sustained rise in serum potassium and a reduction in serum sodium and chloride. Piretanide had minimal effects on serum electrolytes.

New drug evaluations amiloride (Midamor, Merck, Sharp and Dohme)

Amiloride is a potassium-sparing diuretic that is pharmacologically similar to triamterene. It has been widely used abroad for several years, alone and in combination with hydrochlorothiazide. As a potassium-sparing agent, amiloride appears to be approximately as effective as triamterene and spironolactone and to have a longer duration of action than triamterene, allowing once daily dosing. The diuretic effect of amiloride is mild, as are all agents that act at distal tubular sites. Amiloride appears to have an antihypertensive effect approximating that of the thiazides and spironolactone-an advantage over triamterene, which is devoid of antihypertensive effects. Amiloride will probably be most useful as a potassium-sparing agent in combination with the thiazide and loop diuretics. It should be kept in mind, however, that many patients on thiazide diuretics do not need supplemental potassium or potassium-sparing agents if they have no other complicating factors, such as digitalis therapy. When hypokalemia causes symptoms, a potassium-sparing agent have advantages over oral potassium supplements in patient tolerance and compliance. Because of the possibility of tumorigenicity and estrogenic side effects, spironolactone's popularity has been decreasing in recent years. Amiloride will probably be a strong competitor of triamterene and spironolactone because of its longer duration of action than triamterene and, from early indications (cf. ticrynafen), more benign side effects than spironolactone. The drug should be used with great caution, if at all, in patients with impaired renal function, however. The benefits of amiloride will have to be weighed against the cost of the drug in individual patients.