Effects of two diphosphonates (EHDP and Cl2MDP) on serum uric acid in pagetic patients

The effects on serum uric acid (SUA) of two diphosphonates (EHDP at 5 and 20 mg/kg/day and Cl2MDP at 400 and 1600 mg/day) were studied in 49 pagetic patients treated for 6 months. Patients were divided into two groups: group I, initially normouricemic (SUA less than 385 mumol/l); group II, initially hyperuricemic (SUA greater than or equal to 385 mumol/l). SUA was significantly decreased (P less than 0.01) after 6 months of diphosphonate therapy in all group II patients. However, 3 months after withdrawal of therapy, SUA returned to values not significantly different from those initially recorded in this group. SUA did not change during or after treatment in the group I patients. Groups I and II could not be differentiated on the basis of initial serum alkaline phosphatase or urinary hydroxyproline values. In response to therapy, both groups showed the same reduction in these parameters. These results suggest that diphosphonates have no effect at a single level in uric acid metabolism. They certainly reduce the part of the urate pool coming from the nucleic acids of the increased bone cell population by reducing the number of osteoclasts and osteoblasts, which is extremely high in pagetic bone. They also must act on uric acid metabolism through other mechanisms which need to be investigated in further studies.