A Study of Two Doses of MRC375 in Moderate to Severe Rheumatoid Arthritis Patients

This is a double-blind, randomized, placebo-controlled study to assess the safety and efficacy of MRC375 at 75 mg or 150 mg with matching placebo (taken tid with meal or light snack) in patients with moderate to severe RA. Patients will be randomized to one of the following study arms for 24 weeks: * Treatment 1, Placebo: 2 tablets taken tid * Treatment 2, MRC375: 1 tablet of 75 mg tetracycline HCL plus 1 matching placebo tablet taken tid. Total daily dose = 225 mg. * Treatment 3, MRC375: 2 tablets of 75 mg tetracycline HCL taken tid. Total daily dose = 450 mg. Study medication should be taken within 30 minutes of a meal or light snack (either before or after).