OM-8980 - AN INITIAL REVIEW OF ITS PHARMACOLOGY AND THERAPEUTIC POTENTIAL IN RHEUMATOID-ARTHRITIS

OM-8980 is a slow-acting antirheumatic drug (SAARD). It is a glycoprot ein extract of Escherichia coli, with immunomodulatory properties (unr elated to endotoxin) that include effects on cell-mediated and humoral mechanisms. These effects may account for its efficacy in rheumatoid arthritis, although the precise mode of action of OM-8980 in this sett ing is unknown. In several randomised double-blind comparative clinica l trials in patients with rheumatoid arthritis of generally mild to mo derate severity, oral administration of OM-8980 24 mg/day for 6 to 12 months was associated with significant improvements in clinical measur es of the disease and reductions in nonsteroidal anti-inflammatory dru g and/or corticosteroid use. OM-8980 was also well tolerated in clinic al investigations; most adverse. events were minor, transient, and mai nly gastrointestinal in nature. The drug did not induce circulating au toantibodies or immune complexes. In 2 investigations, OM-8980 showed greater efficacy than placebo without intergroup differences in tolera bility. Compared with other SAARDs, OM-8980 was as effective as aurano fin or penicillamine and was better tolerated than either; however dos ages of the latter drugs did not exceed the lower dosage ranges used c linically. A comparative trial with methotrexate (which appears the mo st appropriate SAARD in this setting) is lacking.The beneficial effect s and favourable tolerability of OM-8980 were also maintained with lon g term (median 5 years) administration in a small noncomparative retro spective investigation. While this study provided evidence of sustaine d efficacy without significant adverse events, the final results of an ongoing prospective trial are awaited to confirm these findings. Thus , although further studies are required to consolidate the clinical pr ofile of OM-8980, preliminary data indicate a role for this drug as se cond-line therapy for rheumatoid arthritis where methotrexate is inapp ropriate. Furthermore, given its favourable tolerability demonstrated thus far OM-8980 may find particular use during earlier stages of the disease where the adverse effects of some other SAARDs might preclude their use.