Efficacy of Rhenium-186-Etidronate in Prostate Cancer Patients with Metastatic Bone Pain

Rhenium-186-etidronate has been developed for pain relief of bone metastases and has previously been studied with regard to toxicity, pharmacokinetics and dosimetry. Its palliating effect on bone pain has not been studied extensively. To justify further efficacy investigations, patients participating in two toxicity studies were studied using a strict pain assessment methodology. Forty-three patients entered the study, 37 of whom were evaluable for pain assessment. Administered dosages ranged from 1295 MBq (35 mCi) to 3515 MBq (95 mCi) 186Re-etidronate. Pain relief was assessed using a handwritten diary containing questions reflecting the multidimensional character of chronic pain. The diary was marked twice daily for a maximum of 10 wk (2 wk prior to and 6/8 wk after the injection). A response was determined using a specific decision rule, in which pain intensity, medication index and daily activities were core determinants. A response was reached in 54% (20 of 37) of the patients and varied from 33% (n = 6) in the "35-mCi" group to 78% (n = 7) in the "50/65-mCi" group to 70% (n = 7) in the "80/95-mCi" group. Pain assessment using the multidimensional pain model showed that 186Re-etidronate is an effective agent in the treatment of metastatic bone pain in prostate cancer and warrants further placebo-controlled studies.