the bisphosphonates of formula r . sub . 2 -- x --. sub . m1 -- cr . sub . 3 r . sub . 4 -- ch . sub . 2 -- cm 2 ] 2 bicyclic bisphosphonates , and cyclic bisphosphonates are useful as anti - arthritic agents and do not have the side effects of anti - arthritic agents which are prostaglandin synthetase inhibitors .