EFFECT OF ACID-PHOSPHATE VS. NEUTRAL-PHOSPHATE ON URINE ACIDITY, ACID-BASE BALANCE, AND MINERAL HOMEOSTASIS IN CHILDREN WITH FAMILIAL HYPOPHOSPHATEMIC RICKETS (XLH). [Abstract only] Uri S. Alon, Wayne Moore, David Schwartz, Sections of Nephrology and Endocrinology, Children's Mercy Hospital, Kansas City, MO, Univ of Missouri, Kansas City, MO.

A common complication of treatment of children with XLH is the development of nephrocalcinosis (NC). Previous studies demonstrated the NC to be related to the high doses of phosphate, and to be composed of CaP precipitates (J Peds 1992; 120:899). Crystalization [sic] of CaP in the renal tubule depends on urine pH: urine acidification protects animals from phosphate-induced NC (Ped Res 1993;33:351A). Presently we compared the effects of Neutral-Phosphate (NP), the traditional preparation used to treat XLH, and a commercial phosphate urine acidifier (AP) on urine acidity, systemic acid-base balance and mineral homeostasis. Eleven children (M 4) with XLH were studied; 7 were already receiving treatment with NP and calcitriol. After collecting data on the 4 new patients, they were also treated with calcitriol and NP. After 6months on the NP therapy all patients were switched to AP, maintaining the same doses of inorganic P and calcitriol for 6 more months. Patients were seen in the clinic every two to three months. On each visit a fresh urine specimen was analyzed for Cl, HCO3, Ca, P, alkaline phosphatase and PTH. Two-three specimens were collected on each patient in each study period. The median values were used for statistical analysis. Skeletal surveys were obtained at the end of each study period. Results (mean +/- SD): Urine pH increased from 6.45 +/- 0.43 in untreated patients to 6.92 +/- 0.32 with treatment with NP (P< 0.05). The change to AP decreased urine pH to 6.06 +/- 0.32 (P < 0.05 Vs. untreated, P < 0.001 Vs. NP). There were no differences between the effects of NP and AP on urine Ca/creatinine ratio, serum Ca, P, PTH, Cl, HCO3, but during AP treatment alkaline phosphatase activity was lower than during NP, 330 +/- 121 Vs. 388 +/- 117 u/l (P < 0.01). Radiographs showed on-going healing of rickets with both preparations. We conclude that a change in the treatment ofXLH from NP to AP significantly lowers urine pH without having adverse systemic effects and therefore has the potential of decreasing the incidence of NC. A long-term clinical study on the use of AP in treating XLH is underway.