Doxycycline Antibiotic Might Help Treat Arthritis

"Osteoarthritis is the most common human joint disorder in the world, and in the equine industry it's the most economically important disease," said Ashlee Watts, DVM, a graduate student at Cornell University, during the 2007 American Association of Equine Practitioners Convention, held Dec. 1-5 in Orlando, Fla. "It's the primary cause of decreased athletic function and wastage in racehorses."

Many medications have been tried to treat this common condition, and Watts discussed the relatively new option of doxycycline for arthritis. Doxycycline is a semisynthetic antibiotic that's related to tetracycline and has been used in horses since the 1990s. It's also used to treat Lyme disease, and one study on that disease noted that horses given the medication along with other antibiotics "never went better," despite being negative for Lyme disease, suggesting a possible anti-inflammatory effect. Therefore, researchers decided to investigate its possible use against osteoarthritis. (Lisa Fortier, DVM, PhD, Dipl. ACVS, associate professor of veterinary clinical sciences at Cornell University, was the principal investigator on the study.)


Doxycycline might indeed be therapeutic for osteoarthritis, laminitis, and neuropathy (nerve dysfunction), and it might be useful for prophylaxis in high-risk cases.

Previous laboratory research found that at concentrations as low as 0.0462 microliters (�g/mL) in synovial (joint) fluid and plasma, doxycycline could inhibit the expression of matrix metalloproteinases 3 and 13 (MMP 3 and 13). Various MMP enzymes have been implicated in osteoarthritic and laminitic disease processes, so inhibiting them might help slow these disease processes. However, antibiotics shouldn't be used at antimicrobial levels (which are substantially higher than 0.0462 microliters (�g/mL) without good reason, because this might promote antibiotic-resistant bacteria strains.

To determine if oral dosing could deliver enough doxycycline (0.0462 �g/mL) to joints without having antimicrobial effects, researchers fed six healthy horses 5 mg/kg (half the recommended antimicrobial dose) every 12 hours via nasogastric tube for two days. This dosing strategy was, indeed, effective at achieving therapeutic concentrations in the joints, Watts reported; levels reached 0.1943 �g/mL by one hour after administration and increased thereafter.

Thus, doxycycline might indeed be therapeutic for osteoarthritis, laminitis, and neuropathy (nerve dysfunction), and it might be useful for prophylaxis in high-risk cases. Possible concerns with doxycyline use include photosensitization (horse becomes overly sensitive to light) and whether it can be performance-enhancing in addition to disease-modifying.

"Further in vivo studies are warranted to determine if MMP activity is inhibited in vivo and to fully elucidate a medication protocol," she concluded.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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