Interrelationships among thiazide diuretics and calcium, magnesium, sodium, and potassium balance in normal and hypertensive man.

The benzothiadiazide diuretics are known to cause magnesium and potassium wasting and retention of calcium and uric acid. The effect of magnesium replacement on diuretic-induced changes in sodium, potassium, calcium, and magnesium balance, weight, and blood pressure was studied in 12 normal subjects and 13 hypertensive patients to determine whether oral magnesium would reduce thiazide-induced kaliuresis. The groups differed in their response to diuresis in that the normotensive subjects did not show a fall in blood pressure (despite an equivalent weight loss), returned to a state of sodium balance earlier, and developed a greater net negative potassium balance over 12 days of diuretic therapy. Both groups displayed calcium and uric acid retention and magnesium wasting during diuretic therapy. The addition of oral magnesium replacement during diuretic therapy had no effect on any measured values beyond that seen in subjects who took diuretics without magnesium replacement. Thus, magnesium replacement did not reduce urinary potassium loss. However, urinary calcium losses increased when magnesium was given to subjects who were not receiving diuretics. The data provide the first report that small doses of oral magnesium enhance calcium excretion in hypertensive subjects.