Potassium

Overview

Potassium is the principal cation (positively charged element of an electrolyte) of intracellular fluid with a concentration of 140 mmol/L. The extracellular fluid potassium concentration is 3.5 to 5.5 mmol/L, making it thirty times less concentrated than the intracellular fluid. Together with sodium, the principal cation of the extracellular fluid, potassium maintains the potential difference across cell membranes. The importance of potassium's contribution to this function is best demonstrated by the consequences of hyperkalemia (increase in extracellular potassium concentration) and hypokalemia (decrease in extracellular potassium concentration) on the heart. Both conditions result in abnormal depolarization and repolarization of cardiac cells, leading to potentially fatal cardiac arrhythmias and conduction disturbances.

Other physiologic functions in which potassium plays a role include energy metabolism, membrane transport, normal water balance, acid–base balance, and osmotic equilibrium. The relationship of potassium and sodium is essential to good health, with a ratio of dietary potassium to sodium recommended at 5:1.

Recent studies have provided strong evidence that potassium may have an antihypertensive function. A meta-analysis of 33 randomized controlled clinical trials with about 2,600 participants demonstrated that potassium supplementation was associated with a significant reduction in mean systolic and diastolic blood pressure. The mechanisms behind the blood pressure–lowering effects of potassium include effects on natriuresis, the renin-angiotensin-aldosterone system, direct vasodilatory functions, baroreflex sensitivity, and catecholaminergic functions as well as an improvement of glucose tolerance.

Other studies suggest that there may be a role for potassium together with glucose and insulin in the reduction of acute myocardial infarction (MI) mortality. Glucose-insulin-potassium (GIK) treatment was shown to decrease acute MI mortality by itself or in combination with thrombolytic therapy, revascularization procedures, or both. A possible mechanism of GIK action is decrease of circulating levels of free fatty acids (FFA) and myocardial uptake of FFA.

Studies have revealed that the elderly are at high risk for hyperkalemia. The aging process alters normal renal function, leading to an inhibition of normal potassium excretion. In this setting of impaired renal function, several drugs which are commonly prescribed to the elderly can further alter the kidney's ability to excrete potassium, leading to hyperkalemia and a potentially life-threatening situation.

Dietary Sources

The richest dietary sources of potassium are fresh unprocessed food including meats and fish, vegetables (especially potatoes), fruits (especially avocados), and citrus juices. Ample potassium can be obtained by a varied diet with adequate intake of milk, meats, cereals, vegetables, and fruits.

Constituents/Composition

Potassium is a metallic element of the alkali group with an atomic weight of 39 and atomic symbol of K. It is the chief intracellular cation; 98% of total body potassium is found in the intracellular fluid.

Commercial Preparations

Potassium supplements are usually available in the form of potassium salts or potassium bound to mineral chelates. These include the following.

• Potassium acetate
• Potassium bicarbonate and potassium citrate effervescent
• Potassium chloride
• Potassium gluconate

Potassium is also sometimes included in multivitamin preparations.

Therapeutic Uses

• To treat the symptoms of hypokalemia
• To control and prevent hypertension
• To reduce the mortality associated with acute MI (used in combination with glucose and insulin)
• To counteract glucose intolerance
• To protect against stroke
• To treat cardiac arrhythmias
• To treat muscle weakness
• To assist in the treatment of diabetes mellitus

Dosage Ranges and Duration of Administration

The average potassium intake estimated by the National Research Council is as follows.

• In infants: 780 mg/day
• In children: 1,600 mg /day
• In adults: 3,500 mg/day

There is no recommended increased intake of potassium during pregnancy and lactation.

Side Effects/Toxicology

Side effects from prescribed use include the following.

• Gastrointestinal (stomach pain, nausea, vomiting, diarrhea, flatulence)
• Cardiovascular (bradycardia)
• Metabolic, endocrine (hyperkalemia)
• Respiratory (weakness, difficult breathing)
• Local tissue necrosis with extravasation

Toxic effects due to overdose include the following.

• Muscle weakness
• Lethargy
• Gastric hypomotility
• Paralysis
• Cardiac arrhythmia
• Conduction disturbances
• Death

Warnings/Contraindications/Precautions

Use with caution in patients with renal insufficiency. Should not be used in patients with severe renal impairment. Because renal function declines with age, the elderly are at high risk of renal insufficiency. Care should be taken when prescribing potassium supplements to the elderly.

Interactions

Angiotensin-Converting Enzyme (ACE) Inhibitors

ACE inhibitors may produce hyperkalemia, particularly when used in combination with nonsteroidal anti-inflammatory drugs (NSAIDs), potassium-sparing diuretics, potassium supplements, potassium-containing salt substitutes, and in patients with autonomic neuropathy, adrenal insufficiency, renal impairment, and diabetes mellitus (Howes 1995; Shionoiri 1993). For this reason, potassium supplements may not be warranted in patients taking these medications; serum potassium levels should be monitored closely.

Beta-Adrenergic Blockers

Beta-adrenergic blockers may elevate potassium levels by promoting a redistribution of this electrolyte (Preston et al. 1998). Potassium levels should be monitored in patients taking these medications, particularly in patients with compromised renal function.

Cyclosporine

Cyclosporine may induce hyperkalemia by decreasing renal excretion of potassium and interfering with aldosterone production or secretion (Preston et al. 1998). Potassium levels in patients on cyclosporine therapy, particularly those with renal insufficiency, should be monitored carefully.

Digoxin

Hypokalemia increases the risk of cardiac glycoside toxicity (Whang et al. 1985). Normal levels of potassium should be maintained during digoxin treatment.

Heparin

Heparin may contribute to hyperkalemia by impairing renal excretion of potassium as a result of interference with aldosterone production or secretion (Preston et al. 1998). Serum potassium levels should be monitored in patients on heparin therapy, especially if potassium supplements are added to the medication regimen.

Nonsteroidal Anti-inflammatory Drugs (NSAIDs)

NSAIDs can affect renal function and decrease potassium excretion (Brater 1999). Hyperkalemia can occur in patients with mild renal insufficiency or normal renal function. Ibuprofen may increase the risk for renal insufficiency and cause hyperkalemia in patients that are over 76 years old, on diuretic therapy, or who have cirrhosis and renal vascular disease (Blackshear et al. 1983; Poirier 1984; Whelton, et al. 1990). Individuals taking these medications should avoid potassium supplements.

Trimethoprim; Co-Trimoxazole

Standard doses of trimethoprim monotherapy as well as trimethoprim combined with sulfamethoxazole have been shown to cause hyperkalemia in a significant number of patients treated for various infections (Alappan et al. 1996; Perazella 2000). Patients treated with these medications should be closely monitored for hyperkalemia, especially those with renal insufficiency (Alappan et al. 1996).

References

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