The effects of potassium supplements, spironolactone of amiloride on the potassium status of patients with heart failure

Hypokalemia in cardiac decompensation

The problem of hypokalemia in cardiac decompensation is reviewed. Some methodological sources of error in connection with blood sampling is discussed, as is the definition of hypokalemia. "Hypokalemia" may be present with a serum potassium value within the reference range of 3.5-5.0 mmol/l. Although diuretics are the most common cause of hypokalemia in patients with cardiac decompensation, there are other factors at work. One is an increase of the plasma aldosterone concentration and another the increased sympathetic nervous activity--adrenaline administration reduces the plasma potassium concentration. The clinical importance of hypokalemia, especially for cardiac arrhythmias, is discussed.

Total body electrolyte composition in patients with heart failure: a comparison with normal subjects and patients with untreated hypertension

Total body elemental composition was measured in 40 patients with well documented heart failure who were oedema-free on digoxin and diuretics. The results were compared with values for 20 patients with untreated essential hypertension matched for height, weight, age, and sex. Total body potassium alone was also measured in 20 normal subjects also matched for anthropomorphic measurements. Patients with hypertension had a very similar total body potassium content to that of normal subjects, but patients with heart failure had significantly reduced total body potassium. This could not be explained by muscle wasting because total body nitrogen, largely present in muscle tissue, was well maintained. When total body potassium was expressed as a ratio of potassium to nitrogen mass a consistent depletion of potassium was revealed in the group with heart failure. Potassium depletion was poorly related to diuretic dose, severity of heart failure, age, or renal function. Activation of the renin-angiotensin-aldosterone system was, however, related to hypokalaemia and potassium depletion. Such patients also had significantly lower concentrations of serum sodium and blood pressure. Serum potassium was related directly to total body potassium. Despite the absence of clinically apparent oedema total body chlorine was not consistently increased in heart failure, but the calculated extracellular fluid volume remained expanded in the heart failure group. Total body sodium was significantly increased in patients with heart failure, but less than half of this increase could be accounted for by extracellular fluid volume expansion. Potassium depletion in heart failure may account in part for the high frequency of arrhythmias and sudden death in this condition.

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.

Fixed combination drug therapy

Almost half of all marketed drugs are fixed combination preparations, yet the World Health Organization included only 7 in its list of 240 "essential' drugs. There has been little scientific study of these preparations but much emotion and rhetoric has been expended both for and against them. Potential advantages of fixed combination preparations include: increased compliance, synergy and increased efficacy, and reduced side effects and cost. Potential disadvantages include: inflexible fixed dose ratio, incompatible pharmacokinetics, increased toxicity, and physician and pharmacist ignorance of content. There are a few combinations of undisputed value such as oral contraceptives, levodopa with decarboxylase inhibitors, and pyrimethamine with sulphadoxine. In other cases fixed-dose combinations may have value in strictly specified circumstances, but are probably overprescribed. There is also widespread, unjustified use of combinations in over-the-counter preparations which may have unrecognised adverse effects. Combinations should only be used if each component is necessary for the desired effect and if the advantages outweigh the added risks of using 2 or more drugs. Before prescribing combination drugs, clinicians should always ask themselves a series of questions of which the most important is whether the patient needs each drug in a particular combination, or if 1 component alone would be adequate. In general, government regulatory bodies in "developed' countries are attempting to curb the use of combination drugs, but a more profitable approach might be to better educate doctors on both the advantages and disadvantages of fixed combination preparations leading to improved prescribing habits.

Diuretics and the institutional elderly: a case against routine potassium prescribing

In 14 elderly male residents of a veterans' care complex who were receiving diuretic therapy for cardiac failure, oral potassium (K) supplements were withdrawn. Plasma and erythrocyte K levels were measured immediately before and six weeks after withdrawal of the supplements (38 mEq K daily). The controls comprised 19 elderly residents without disease and not taking drugs likely to influence K status. Study subjects and controls were receiving the same diet (average daily K content 100 mEq). After withdrawal of K supplements, the mean plasma K level fell significantly but the mean erythrocyte K level remained unchanged and did not differ from the control values. For a further six weeks after the withdrawal period, 7 subjects were treated with Aldactazide (diuretic hydrochlorothiazide plus K-sparing spironolactone). The plasma K level increased significantly but the erythrocyte K level remained unchanged. It was concluded that, in this setting, diuretic-induced hypokalemia is not necessarily accompanied by intracellular K depletion and that routine prophylaxis with K supplements or K-sparing agents is unnecessary and not without risk. Such therapy should be reserved for patients considered at special risk of K depletion because of known poor dietary intake, advanced liver disease, secondary hyperaldosteronism with renovascular hypertension, gastrointestinal losses, or nondiuretic medication known to affect K status adversely.