Prednisone, a glucocorticoid, increases renal potassium excretion, leading to hypokalemia. This occurs primarily through two mechanisms: Firstly, prednisone enhances the activity of the mineralocorticoid receptor in the kidneys. This receptor, usually bound by aldosterone, regulates sodium and potassium reabsorption. Prednisone’s binding stimulates sodium retention and potassium secretion in the distal nephron, increasing potassium loss in urine. Secondly, prednisone boosts the activity of the enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2). This enzyme converts cortisol (a weak mineralocorticoid) to cortisone, preventing cortisol from binding to the mineralocorticoid receptor and competing with aldosterone. Prednisone’s presence indirectly increases the availability of the receptor for aldosterone, further amplifying sodium retention and potassium excretion.
Other Contributing Factors
Beyond these primary mechanisms, increased gluconeogenesis induced by prednisone can indirectly contribute to potassium depletion. Gluconeogenesis, the process of glucose synthesis from non-carbohydrate sources, requires potassium. Therefore, enhanced gluconeogenesis shifts potassium from the extracellular fluid into cells for this process, lowering serum potassium levels. Finally, prednisone can cause gastrointestinal upset, leading to vomiting or diarrhea. This can result in potassium loss through the digestive system, exacerbating the hypokalemia.
