Objective: The efficacy of erythromycin in treatment of knee effusion due to osteoarthritis was evaluated.

Method: We assessed efficacy and safety of erythromycin during 16 weeks in patients enrolled in a randomized double-blind study. One hundred and eight patients with knee effusion due to osteoarthritis (OA) received 12-week courses of erythromycin or placebo allocated randomly, and were followed for 4 months. Acetaminophen 650 mg/day was used in both groups, while they received no other anti-inflammatory drugs (such as corticosteroid or nonsteroidal anti-inflammatory drugs) during the course of the study. Our patients were divided in two groups, erythromycin in doses of 200 mg four times per day was given to the first group (51 patients) over the first 3 months of the study and in the second group we used placebo with the same dosage and schedule (53 patients). Outcomes improvement for the erythromycin-treated group was assessed by a significantly higher mean score from baseline to the end of the trial, compared with placebo group. Patients were examined monthly during the treatment period. Measurement values included recording of Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire subscales (pain, stiffness and function), range of motion and knee circumference.

Results: Erythromycin produced a higher response rate than placebo in treatment of knee effusion due to OA. Significant reduction in knee circumference (P < 0.0005) and pain (P < 0.001) with functional improvement (P < 0.0005) were seen. At the first month after treatment, 11.8% (6 patients) in erythromycin and 9.4% (5 patients) in placebo groups had 50% pain reduction, which was not significant (P = 0.75). At the fourth month, 50% reduction of pain was seen in 45.1% (23 patients) of the erythromycin and 11.3% (6 patients) of the placebo group. This was statistically significant (P < 0.0005). Erythromycin treatment was well tolerated and mild adverse events caused no discontinuation during the study.

Conclusion: This is a placebo-controlled study of macrolid efficacy on knee effusion due to OA in a short period. Results of this research showed the better efficacy of erythromycin in controlling effusion and pain with functional improvement in patients with knee effusion due to OA.