Bisphosphonates in prostate carcinoma

The majority of the patients with advanced prostate carcinoma have painful skeletal metastases, which are responsible for significant skeletal morbidity and disability. Most of these metastases are osteosclerotic, but it has been shown that the abnormal osteoblastic bone formation within metastases is preceded by osteoclastic activation, which appears to be associated with bone pain. This provides the rationale for using bisphosphonates, which are powerful and selective inhibitors of osteoclastic bone resorption. Several bisphosphonates have been shown to be clinically useful for the treatment of several conditions characterized by abnormal osteoclastic bone resorption, including Paget's disease, primary hyperparathyroidism, myelomatosis, and skeletal metastases. Its efficacy in relieving pain in patients with skeletal metastases due to prostate carcinoma has been confirmed in a few studies. The bisphosphonate clodronate was extensively investigated in the study unit. When infused intravenously i.v. (300 mg/day) relief of bone pain become appreciable within 3 days, sometimes preceded by a transient pain flare. These clinical results are very consistent and the residual pain usually is of extraosseous origin. Thus, with regard to pain of strictly bone origin, unresponsive patients are quite rare. Oral administration also is effective, but due to its limited intestinal absorption the effective dose is on the order of 1600-3200 mg/day. These doses usually are well tolerated, but they may be a problem for severely ill patients. Furthermore, the efficacy of treatment becomes apparent only after a few days. Thus, oral clodronate usually is adopted as a continuation of an i.v. course. The duration of the i.v. therapy should be individualized, but usually the more prolonged the treatment the longer the duration of the effect. For practical reasons, clodronate is infused daily for 5 days (Monday-Friday) and the treatment course is repeated at the time of any significant recurrence. The oral continuation prevents or delays the recurrence of bone pain in most patients, but in some patients this therapy has to be integrated occasionally with i.v. infusion. The duration of the effect for the same bioavailable dose is somewhat related to the degree of malignancy of the primary tumor. In an uncontrolled study, the author also evaluated the effectiveness of alendronate given either i.v. or orally. A single infusion of 5 mg alendronate i.v. produces roughly the symptomatic effect of 5 i.v. infusions of 300 mg clodronate. Alendronate, 40 mg orally/day, was effective in reducing bone pain in 11 of 12 patients with bone metastases due to prostate carcinoma but who were not confined to bed. In some patients with prostate carcinoma and a diffuse metastatic invasion of the skeleton, there is indirect biochemical and histologic evidence of osteomalacia. This can be aggravated by bisphosphonate administration because of the transient striking prevalence of osteoblastic activity over bone resorption, which also occasionally causes the appearance of symptomatic hypocalcemia. Therefore, the use of large oral supplements of calcium is recommended, particularly at the start of therapy. It is conceivable that these calcium supplements also may be able to improve the final clinical outcome of the bisphosphonate therapy. In conclusion, administration of large doses of bisphosphonates is one of the most cost-effective palliation treatments for patients with prostate carcinoma with bone metastases, both as first-line therapy and in the long term. With appropriate doses, a large proportion of patients can be maintained free of bone pain until death. Studies of the ability of lower doses to prevent skeletal morbidity in patients without metastases or with asymptomatic bone lesions are warranted.