It is true that an antibiotic—doxycycline—has been evaluated in the treatment of OA. In studies employing animal models of OA, this drug has been shown to prevent or slow the progression of OA. It is theorized that doxycycline can decrease the amount of cartilage-degrading enzymes found around the joints.
The results in human trials were equivocal, however, and doxycycline had not shown much promise for OA in the past.
However, a recently published medical study offers some hope. In this study, obese women with OA-related pain in one knee took 200 milligrams per day of doxycycline for 30 months. Another group of women with similar symptoms were given sugar pills (placebo) to take every day.
The patients' pain was assessed at each visit, and x-rays were taken at the beginning and the end of the study. At the end of 30 months, the women who were treated with doxycycline were compared with those who took sugar pills. The results showed that women who took the doxycycline had less pain and less cartilage degradation, as compared to the women who took the sugar pills.
This study is encouraging, but because of several limitations in its design, we cannot say for sure that everyone with OA should start taking doxycycline. For example, the study included only middle-aged women, which begs the question, “Would doxycycline also work in men?”
Additionally, the study examined a relatively small number of people (431) and evaluated them over a relatively short period of time. Would the results have been better or worse if the doxycycline therapy was continued? Experts have suggested that before doxycycline can be recommended as a treatment, larger studies must be done. The populations of the studies should include men and women as well as people from a variety of ethnic backgrounds. Until this kind of research is carried out, doxycycline should not be routinely prescribed for people with OA.