The comments by Drs Leslie and Wang on the importance of magnesium are greatly appreciated. The concept that magnesium is an important regulator of potassium homeostasis has gained popularity during the last few years, although convincing evidence is lacking for most diuretic-treated patients. Magnesium is mainly an intracellular cation, as is potassium, and serum levels in general do not correlate well with intracellular stores, thus making the assessment of magnesium status difficult by usual laboratory techniques. Magnesium is excreted into the urine at the level of the loop of Henle, and, therefore, loop diuretics are the more likely agents to cause magnesium depletion. Thiazide diuretics are less likely to cause significant magnesium depletion, especially in patients with systemic hypertension but without other complications.
In our study,1 the role of magnesium was considered and plasma magnesium levels were measured concomitantly with plasma potassium levels at each visit. Thus, six