A Cochrane review included 2 studies with a total of 663 subjects. The first study randomized 431 obese women with radiologically confirmed osteoarthritis of the knee to receive doxycycline 100 mg or placebo twice a day for 30 months. The other study included women and men with radiologically confirmed osteoarthritis of the knee, who were randomly allocated to receive doxycycline 100 mg or placebo twice a day for 24 weeks.
At end of treatment, clinical outcomes were similar between the two treatment groups (Table ). More patients withdrew from the doxycycline group (39/1000) compared with placebo (17/1000) due to adverse events (RR 2.28, 95% CI 1.06 to 4.90; 2 studies, n=663). Number needed to harm (NNTH) was 46 (95% CI 15 to 980). There was no evidence that participants in the doxycycline group experienced more serious adverse events than those in the placebo group, but the estimate was imprecise (RR 1.07, 95% CI 0.68 to 1.68; 2 studies, n=663).
| Outcome | Number of participants (studies) | Assumed change (placebo) | Corresponding change (doxycycline) | Difference between doxycycline and placebo (95% CI) |
|---|---|---|---|---|
| Decrease in pain (10-cm VAS scale); median follow-up 18 months | 524 (2) | 1.8 cm decrease in pain pain on 10-cm VAS | 1.9 cm decrease in pain on 10-cm VAS | Δ -0.1 cm (-0.6 to +0.3 cm) favouring doxycycline |
| 29% improvement | 32% improvement | Δ 3% (-5% to 10%) | ||
| Function (WOMAC function, range 0 to 10); median follow-up 18 months | 517 (2) | 1.2 units improvement on WOMAC | 1.4 units improvement on WOMAC | Δ -0.2 ( -0.5 to +0.2) favouring doxycycline |
| 21% improvement | 24% improvement | Δ 3% (-3% to 10%) | ||
| Changes in minimum joint space narrowing; follow-up 30 months | 361 (1) | 0.45 mm change | 0.30 mm change | Δ -0.15 mm ( -0.28 to -0.02 mm) favouring doxycycline |
Comment: The quality of evidence is downgraded by study limitations (unclear allocation concealment and failure to adhere to the intention-to-treat principle).