Intraarticular minocycline injection in experimental synovitis.

Minocycline, a semi-synthetic tetracycline, was injected into one hind joint of twenty-two rabbits with zymosan-induced arthritis, while the contralateral joint served as a control. A local inflammatory reaction was observed a few days after the zymosan injection. Most clinical parameters such as knee diameter, systemic temperature, sedimentation rate and blood cell count did not change throughout the experiment both in control and minocycline treated rabbits. However, the zymosan platelet counts rose from 3.4x10(5)/microL to 5x10(5)/microL, as well as the level of serum fibrinogen (from 99 mg% to 370 mg%). Microscopically, a perivascular infiltrate consisting of lymphocytes and polymorphonuclear cells was seen. Lymphoid follicles as well as plasma cells epitheloid and giant cells were also observed. A mild tendency to fibrosis and lesser inflammatory reaction in the minocycline treated knees was noted. Our data suggest that intraarticular minocycline treatment did not alleviate the course of the rheumatoid-like inflammatory reaction of the knee joint.