Evaluation of Subantimicrobial Dose of Oral Coxycycline for the Treatment of Periodontitis in Dogs

Abstract

Periodontal inflammatory disease is one of the most prevalent disease affecting both humans and small animals. Prior to any other treatments for the chronic periodontitis, mechanical removal of plaque and calculus should be achieved. In human medicine, several medical treatment options were established after the periodontal debridement. Subantimicrobial dose of doxycycline (SDD) is one of adjunctive treatments which downregulate the activity of matrix metalloproteinases (MMPs), which are key destructive enzymes in periodontitis in humans. Therefore, the purpose of the present study was to evaluate the SDD of dogs which would not reach the antimicrobial concentration, but had the inhibitory effect of matrix metalloproteinases using experimentally induced periodontitis model. This study consists of three chapters. Chapter I demonstrated the effectiveness of modified silk ligature twisted with wire for the induction of advanced periodontitis. Twenty beagles were divided into 4 groups according to the ligature-inducing materials: soft-moistened food only, wire ligature, silk ligature and silk-wire twisted ligature. Experimental periodontitis was induced by ligation using each material according to the groups on the cervix of 6 teeth in each dog. The periodontal inflammation status was evaluated using clinical periodontal parameters and dental radiography before and 60 days after ligation. The ligatures were checked daily, and the day the ligature fell out was recorded. The silk-wire twisted ligature induced the most intense periodontitis and remained the most stable compared to the other groups (P<0.05). Chapter II demonstrated the identification of SDD for the treatment of periodontitis in dog. Twenty healthy beagles were used for measurement of the serum concentration of doxycycline. The beagles were divided into 4 groups according to the administration dose. Doxycycline hyclate was orally given at a single dose of 1, 2, 3 and 5 mg/kg. Blood samples were collected pre- and post-administration at the same time and the serum concentrations of doxycycline were determined using high-performance liquid chromatography. Mean serum doxycycline concentrations of 1 and 2 mg/kg groups were maintained significantly lower than the minimal inhibitory concentration of doxycycline during 24 hours. The evaluated SDD was used for the assessment of the matrix metalloproteinase inhibitory effects using gelatin zymography. Fifteen beagles with periodontitis were used for the evaluation of the efficacy of SDD for one-month administration. Five beagles were assigned to each group, and each group was orally administrated 0, 1 and 2 mg/kg of doxycycline once a day. Before and after the experimental phase, clinical periodontal status and MMPs expression of periodontium were evaluated. The zymographic intensities which reflected MMPs expression significantly decreased in the SDD administrated groups compared to control group. Clinical improvements of periodontal status were dose-dependent (P<0.05). Chapter III demonstrated the influence of oral administration of SDD to the normal periodontal flora. Experimental periodontitis using the silk-wire twisted ligature were induced in twelve healthy beagles. The dogs were randomly assigned to one of two groups: SDD (doxycycline, 2 mg/kg) and control group. Clinical periodontal status was evaluated and subgingival plaque was sampled on weeks 0, 4 and 8. Sampled plaque was cultured in the completely anaerobic system for one week and the total anaerobes, Porphyromonas spp., Bacteroid spp. and Pasturella spp. were counted. Using the agar dilution method, minimum bactericidal concentration of doxycycline was evaluated and resistance for doxycycline was monitored during experimental phase. The clinical periodontal status of SDD group was significantly improved compared to the control group. All kinds of bacterial counts were not significantly different between the two groups. Antibacterial resistance was not established in the SDD group during the experimental periods (P<0.05). Based on the results of the present studies, oral administration of 2 mg/kg doxycycline, once a day, was identified as appropriate dose for the periodontitis which should not affect the antimicrobial susceptibility of the periodontal flora in the dog. Therefore, it is suggested that once a day oral regimen of 2 mg/kg doxycycline could serve as a SDD for periodontitis in dogs.