Effect of dipyridamole on serum and urinary phosphate in X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is characterized clinically by rickets, hyp ophosphatemia and hyperphosphaturia. Conventional treatment of XLH with ora l phosphate and vitamin D is associated with hypercalcuria and nephrocalcin osis. Recently, intravenous and oral dipyridamole has been reported to decr ease fractional excretion of phosphate in adults with idiopathic hyperphosp haturia. Our objective was to determine whether oral dipyridamole therapy r educes urinary phosphate excretion and increases serum phosphate concentrat ion in children with XLH. A prospective study was performed in six children with XLH. The average age of the patients at the start of the study was 12 .5+/-1.0 years. The effects of 12 weeks of oral dipyridamole therapy, at 4. 4+/-0.4 mg/kg body weight per day, on serum phosphorous, parathyroid hormon e (PTH), 1,25 (OH)(2) vitamin D, osteocalcin, tubular maximum for phosphate reabsorption (TmP/GFR), urinary calcium excretion, and cyclic adenosine 3' ,5'-monophosphate (cAMP) excretion, were compared to baseline levels. Our r esults show that there was no change in serum phosphorous concentration or TmP/GFR after 12 weeks of dipyridamole therapy. Dipyridamole therapy also h ad no effect on serum PTH, serum 1,25 (OH)2 vitamin D, alkaline phosphatase , osteocalcin levels, urinary calcium or cAMP excretion. We therefore concl uded that in children with XLH, a 12-week course of dipyridamole had no eff ect on serum phosphorous or its urinary excretion. Dipyridamole therapy is unlikely to improve the bone disease in children with XLH.