Trichlormethiazide and oral phosphate therapy in patients with absorptive hypercalciuria.

In a short-term prospective study 36 patients with absorptive hypercalciuria were initially treated with diet alone followed by either trichlormethiazide (4 mg. per day) or oral neutral phosphate (1,500 mg. of elemental phosphorus per day) for 6 weeks. Study subjects were then crossed over to the second drug for an additional 6 weeks. In response to dietary treatment urinary calcium decreased from a pre-treatment value of 346 +/- 63 mg. per 24 hours to 308 +/- 90 mg. per 24 hours. Oral phosphate therapy caused a further decrease in urinary calcium to 218 +/- 85 mg. per 24 hours, an over-all decrease of 37 per cent. Parathyroid function did not change significantly with phosphate administration but circulating levels of 1,25-dihydroxyvitamin D decreased by 22 per cent (73 +/- 12 to 57 +/- 16 pg. per ml., p less than 0.001). Pre-treatment renal phosphate threshold did not correlate with the response to oral phosphate administration. Trichlormethiazide treatment led to a 34 per cent decrease in urinary calcium with a mean value on treatment of 228 +/- 80 mg. per 24 hours. 1,25-Dihydroxyvitamin D levels decreased by 10 per cent. Pre-treatment fasting calcium excretion, parathyroid function and 1,25-dihydroxyvitamin D levels did not correlate with the response to trichlormethiazide. We conclude that both drugs by pharmacological means improve the biochemical abnormalities in absorptive hypercalciuria and should be efficacious in its treatment.