Effects of low-dose capecitabine on Samarium-153-EDTMP therapy for painful bone metastases

Samarium-153 (Sm-153)-EDTMP is routinely used for pain palliation in skeletal metastasis, however most patients report partial response. Many strategies have been contemplated to make radiation therapy for pain more effective, one of them being the use of radiosensitizers. Capecitabine is a chemotherapeutic drug and is routinely combined with external beam radiation to make the target more radio-sensitive. Aim of the study was to evaluate whether combining capecitabine in radiosensitizing dose with Sm-153-EDTMP produces superior analgesia compared to Sm alone. Forty-four patients with skeletal metastases from various primaries were randomized into two groups: The study group received 1 mCi/kg Sm-153-EDTMP plus capecitabine (1,650 mg/m²) orally for 8 days (equivalent to four t_½ of ¹⁵³Sm-EDTMP) and the control arm received 1 mCi/kg Sm-153-EDTMP plus placebo for the 8 days. After treatment, the patients were followed up for 12 weeks to evaluate the degree and duration of pain palliation and hematologic toxicity. All 44 patients reported different degrees of pain relief with none reporting complete pain relief for the entire duration of 12 weeks posttherapy observation period. However the level of pain relief obtained in study arm was significantly better than the control arm with mean posttherapy pain score being 1.29 ± 1.05 and 3.59 ± 2.77 respectively with P of 0.001. Transient and mild hematologic toxicity, as determined by World Health Organization criteria, was apparent in both arms without significant differences. The addition of a low-dose of capecitabine significantly enhances the analgesic effect of Sm-153 without any additional side effects