166Ho-Phytate (Holmium-166-Phytate) was developed as an iv radiotherapeutic for the potential treatment of chronic synovitis. 166Ho-Phytate has potential for the treatment of patients with synovitis, rheumatoid arthritis (RA) and seronegative spondylarthritis.

166Ho-Phytate was supposed to enter Phase III trials by June 2005, following a successful Phase I/II trial with 30 months follow-up. The dose used in synovitis patients was 15 mCi in conjunction with triamcinolone acetonide and lidocaine. Only one patient needed a new injection after 12 months follow-up. Development of this drug was apparently not pursued, but in 2012 the Tehran, Iran, group restarted a development project around this drug and this indication.

Target/Mechanism: Brachytherapy – local applications

Leading Emitter: beta electrons (β–)