Reduction of urine oxalate during long-term thiazide therapy in patients with calcium urolithiasis.

We measured urinary oxalate by the method of Hallson and Rose before and during long-term thiazide therapy in 49 patients with recurrent urolithiasis. Urinary oxalate excretion in normal men and women on their usual diets was 38.8 +/- 10.3 mg per day (mean +/- SD) and in patients with calcific renal calculi was 45.9 +/- 14.3 mg per day. Hydrochlorothiazide produced a significant decrease in urinary oxalate excretion in patients treated for more than 12 months (33 +/- 10.6 mg per day). We believe that the thiazide-induced reduction of urinary oxalate excretion is related to reduced intestinal calcium absorption which has been shown during chronic thiazide therapy and may not be evident until 12 or more months of thiazide administration.