Effect of different doses of chlorthalidone on blood pressure, serum potassium, and serum urate.

Chlorthalidone given to 40 hypertensive women significantly decreased blood pressure and serum potassium levels and increased the serum urate concentration. There were no individual correlations between the reduction in blood pressure and the decrease in serum potassium or the increase in serum urate. A reduction in dosage from 50 mg daily to 50 mg three times a week produced no significant changes in the diastolic or mean blood pressures though the systolic blood pressure was moderately increased. Concomitantly, serum potassium increased and serum urate decreased significantly on the lower chlorthalidone dose. We conclude that high doses of oral diuretics compared with lower ones are of limited further benefit and may increase the risk of clinically significant hypokalaemia and hyperuricaemia.