Matrix metalloproteinases (MMPs), which degrade connective tissue, are essential to the inflammatory process of periodontal disease. Doxycycline inhibits MMPs, even at subantimicrobial doses. To identify the subantimicrobial dose of doxycycline (SDD) for treatment of periodontal disease in dogs, 20 beagles received doxycycline hyclate at 0, 1, 2, 3, or 5 mg/kg (n = 5 dogs/ dose group). Serum doxycycline concentrations were measured at baseline and 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8, 12, and 24 hours postadministration; the SDD was identified to be 1 or 2 mg/kg. To evaluate efficacy, 15 beagles with moderate to severe periodontal disease were divided into 3 groups and given doxycycline at 0, 1, or 2 mg/kg q24h for 1 month. Gingival samples were collected and gingival attachment and bleeding upon probing measured at baseline and after 1 month. Results showed significant improvement in gingival attachment and bleeding on probing in the 2 mg/kg group, but not in others. Zymographic analysis showed lower gelatinolytic intensities of MMP in tissue samples in week 4 than in week 0. Doxycycline at 2 mg/kg q24h is an effective SDD for treating periodontal disease in dogs. Long-term treatment with SDDs could improve gelatinolytic inflammatory diseases (eg, periodontitis and arthritis) in dogs.

Commentary
Although this report appeared to have promising short-term results, the information should not be applied in the clinical setting without a long-term benefit and adverse event study in dogs affected with different stages of periodontal disease. Unfortunately, what works in human dentistry cannot always be applied to companion animals. Administering doxycycline to canine patients without eliminating periodontal pockets, extracting teeth affected with advanced periodontal disease, and strict attention to plaque control will not help patients or clients.—Jan Bellows, DVM, FAVD, DAVDC, DABVP

Source
Experimental determination of a subantimicrobial dosage of doxycycline hyclate for treatment of periodontitis in Beagles. Kim SE, Kim S, Jeong M, et al. AM J VET RES 74:130-135, 2013.