Etidronate used in recommended doses (usually 5 mg/kg/day for 6 months) produces symptomatic improvement in approximately 60% of patients. The serum alkaline phosphatase and urinary hydroxyproline are reduced to about 50% of initial values. A sustained remission occurs in many patients and retreatment is usually effective upon relapse. The abnormally elevated osteoclast count and resorption surfaces are reduced, and at the low dose there is no accumulation of osteoid. The medication is generally well tolerated and at the recommended dosage there is no evidence of increased fracture rate.We have previously reported our experience with different doses of etidronate in the treatment of Paget's disease of bone (1-5). The drug was found to significantly lower serum alkaline phosphatase and urinary hydroxyproline in a dose-related fashion (3). There was also a significant reduction in pain found in a doubleblind placebo-controlled trial (1). Studies of bone biopsies showed a reduction in osteoclast number and in marrow fibrosis with appearance of lamellar bone; however, calcification rate was reduced and, at the higher doses, osteoid accumulated (33). It was also found that some patients experienced bone pain (6) and it was suggested that there was an increased incidence of fracture (7) at the higher doses. Thus, the recommended dose of etidronate is, for most patients, 5 mg/ kg/day for a 6-month period. If a dose of 20 mg/kg/day is used at all, it should be limited to 3 months' duration. It is our purpose here to provide further data on the long-term use of the drug at the recommended doses, especially 5 mg/kg/day for 6 months.
MATERIALS AND METHODSAll patients who received therapy were judged to have symptomatic Paget's disease of bone by the investigators. Response in symptoms was evaluated by both the patient and the investigator, and no change, mild, moderate or marked improvement or deterioration was noted. Serum alkaline phosphatase and urinary hydroxyproline were measured as previously reported (3). Iliac crest biopsies were performed after double labeling with tetracycline and measurements were made in Dr. Meunier's laboratory (5,8). The majority of patients were followed in Indianapolis; however, some of the data to be presented are from patients followed by Drs. R. D. Altman, Robert Canfield, and Gerald Finerman, in order to give sufficient numbers for evaluation.
RESULTSClinical improvement is difficult to evaluate unless a double-blind placebo-controlled study is performed. In our initial study of this type, a significant dose-response curve reflecting moderate or marked reduction of pain was found. Canfield et al (6) found better pain relief at the lower doses of etidronate than at the higher doses. Subsequent studies were historically controlled and are thus less reliable in evaluating the effect on pain. However, the percent of patients responding remains quite similar to that seen in the initial report. That study showed that of 24 patients receiving 5, 10, or 20 mg/kg/day, 16, or 67%, had symptomati...