Effects of chlorthalidone on serum and total body potassium in hypertensive patients

Total body potassium has been estimated in 26 hypertensive patients who were hypokalaemic as a result of long-term chlorthalidone treatment (mean 20.5 months), while they were on chlorthalidone and 4 weeks after this had been discontinued. The mean difference amounted to only 95 mEq (not significant). In 6 additional patients not previously treated with chlorthalidone, serial total body potassium estimations revealed a mean potassium deficiency of 245 mEq after 33 days and of 106 mEq after 100 days. These results suggest that the mechanism causing the initial potassium loss is partly reversed or compensated later on. In patients with uncomplicated hypertension, no significant potassium deficiency was detected during long-term treatment. Eighteen of our patients received 39 mEq potassium chloride supplements daily for 4 weeks; this caused a mean rise in serum potassium from 3.23 mEq/l to 3.38 mEq/l (not significant). Total body potassium did not change at all. We conclude that potassium chloride supplements are not an effective treatment of hypokalaemia in this condition. Correction of the extracellular pH by ammonium chloride in 6 patients on chlorthalidone, who demonstrated a slight metabolic alkalosis, gave rise to a mean increase in plasma potassium from 2.78 mEq/l to 2.96 mEq/l (not significant). The hypokalaemia in hypertensive patients on long-term chlorthalidone treatment cannot be explained by either a potassium deficiency or the change in extracellular pH.