Diuretics, magnesium, potassium and sodium.

Diuretics increase renal magnesium excretion and, when chronically administered, decrease intracellular magnesium levels. This deficiency reduces active transport of potassium into the cell and intracellular potassium decreases irrespective of serum potassium levels. Potassium supplementation or the co-administration of potassium-sparing diuretics cannot maintain intracellular potassium at normal levels when intracellular magnesium is reduced. The effects of chronic magnesium supplementation have not been adequately studied. Maintenance of the diuretic dose at an effective minimum and curtailing sodium intake when diuretics are chronically prescribed are the simplest and safest manoeuvres which can be undertaken in order to prevent the occurrence of events usually ascribed to hypokalaemia and in fact principally due to low intracellular potassium which is associated with magnesium deficiency.