Palliative therapy with I-131 labeled bezylidenediphosphonic acid: In vivo kinetics and response to pain induced by bone metastases

I-131 labeled α-amino-(4-hydroxybenzylidene)diphosphonic acid (BDP3) was recently suggested as a palliative acting radiopharmaceutical against pain syndromes associated with disseminated bone metastases. Such an application was supported by the in vivo kinetics of I-131-BDP3 in rats. The authors investigated the palliative effectiveness of I-131-BDP3 in 18 patients with typical pain symptoms induced by bone metastases of various primary carcinoma. The blood clearance was rapid. More than 90% disappeared from the blood pool at 4 hr after injection. The excretion of the activity occured solely through the kidneys and the median total body retention at 48 hr was 51% (range 30-64%). The thyroid activity decreased during therapy indicating no cleavage reactions as long as I-131-BDP3 is bound to the bone tissue. The binding of I-131-BDP3 to bone is very long since the effective half life was in the order of magnitude of the physical half life. Additionally the effective half lifes in the metastatic ares (median 182 hr; range 177-205 hr) proved to be longer than in unaffected areas (145 hr; 140-165 hr). The palliative therapies were performed with doses of 6 - 48 mCi. The response amounted to 44% complete pain relief, 6% substantial pain relief, 22% minimal improvement and 28% no change. The duration of response ranged between 1 and 8 weeks