Preparation and evaluation of a new radiopharmaceutical for radiosynovectomy of medium sized joints: ¹¹¹Ag labeled hydroxyapatite (HA) particles

Radiosynovectomy is one of the treatment modalities for patients suffering from rheumatoid arthritis. Radiosynovectomy consists of intra-articular injection of emitting radionuclide in colloidal or particulate form, which comes in contact with synovium. Compared to surgical synovectomy, radiation therapy is simpler and less traumatic, hospitalization time is shorter; cost is lower and duration of relief is comparable.

Many radionuclides, namely, ¹⁶⁶Ho, ⁹⁰Y, ¹⁶⁵Dy, ³²P, ¹⁹⁸Au and ¹⁸⁶Re have been used for radio-synovectomy. ¹¹¹Ag is a potential therapeutic radionuclide decaying by β^– emission [92% by β⁻(E_βmax = 1.037 MeV) and 8% of the β⁻decay is associated with emission of γ-rays (E_γ =245.4keV I_γ = 1.33%; E_γ = 342.1keV I_γ = 6.7%)]. The half life of ¹¹¹Ag is 7.45d. Because of the production feasibility and suitable nuclear property, ¹¹¹Ag may find use as a suitable radionuclide for radiosynovectomy of joints that are not too large. Hydroxyapatite (HA), Ca₁₀(PO₄)₆(OH)₂ is one of the preferred particulates for this application.

Preparation of ¹¹¹Ag labeled HA was carried out by adding 10–20 mg of HA (200–400 mesh) to a required volume of no-carrier-added ¹¹¹AgNO₃ solution in dilute nitric acid (pH between 2 and 7.0) and purified. Stability of the ¹¹¹Ag –HA particulate suspension in normal saline solution and phosphate buffer was studied for durations extending up to 7 days post labeling. Bio-evaluation of the ¹¹¹Ag-HA particles was carried out by injecting required amount of dose into knee joint of white New Zealand rabbits.

Thus, ¹¹¹Ag-HA particles were successfully prepared with high labeling yield (>97%). Radiochemical purity of ¹¹¹Ag-HA particles was 99.9%. Stability studies for seven days showed that ¹¹¹Ag-HA particles were stable. Preliminary bio-evaluation studies of ¹¹¹Ag-HA particles in rabbit showed promising results.