Formulation of long-acting and controlled release preparations of 2-[(3-chlorophenyl)amino] phenylacetic acid (23CPPA) are disclosed. Long-acting preparations comprise a slow-release formulation coated onto a pharmaceutical composition containing 23CPPA, protect against gastric irritation, slow 23CPPA absorption, extend release of 23CPPA, protect against excessively high 23CPPA blood concentrations, and prolong maintenance of blood concentrations of 23CPPA after administration. Controlled release formulations comprise (a) a core element which is a compressed tablet containing a therapeutic dose of 23CPPA and an amount of a solubility modulating substance that controls the release of said 23CPPA in order to provide a therapeutic level over a period of about 24 hours and (b) on the outer surface of the core element, a sufficient amount of an enteric coating that causes the 23CPPA to release at a rate that permits the use of once-a-day dosing to maintain steady state therapeutic levels of 23CPPA.
