Formulation and preliminary in vivo dog studies of a novel drug delivery system for the treatment of periodontitis.

A novel drug delivery system for the treatment of periodontitis was developed using two components. The first was tetracycline base loaded into the microtubular excipient halloysite, which was coated with chitosan to further retard drug release. Encapsulation efficiencies of 32.5% were achieved with the loading procedure, with tetracycline base showing in vitro release for up to 50 days in simulated gingival crevicular fluid. The second component developed was a vehicle for the drug loaded coated halloysite, which was primarily based on the thermoresponsive polymer, poloxamer 407. A concentration of 20% was chosen with the thermoresponsivity of the system modified using PEG 20,000 so that the mobile product at room temperature would gel by temperature rise following syringing into a periodontal pocket. Retention of the overall system in the pocket was further improved by the addition of octyl cyanoacrylate (OCA). The thermoresponsivity of the poloxamer 407 system proved to be sensitive to the presence of added excipients with the levels of PEG 20,000 and OCA requiring modification in the presence of the halloysite component. A final formulation was developed which consisted of 200 mg of halloysite double loaded with tetracycline base and coated with chitosan, suspended in 1 ml of poloxamer 407 20% (w/w), PEG 20,000 0.5% (w/w), OCA 1.0% (w/w), water to 100%, adjusted to pH 4. The syringeability of this formulation at various temperatures was evaluated to ensure ease of delivery to the periodontal pocket. A stability study was performed to examine the change in thermoresponsivity over time, with the final formulation found to be stable for at least 9 months when stored at room temperature (approximately 20 degrees C). This formulation offered ease of delivery to the periodontal pocket and sustained release of the antibiotic for up to 6 weeks. The formulation had preliminary in vivo testing performed in dogs to determine levels of drug release, antimicrobial activity and retentive ability of the product. A wound pocket creation model was developed for the purposes of the trial. The product was easy to deliver to the pockets with application times of less than 1 min. Results showed the product was retained in the pocket for up to 6 weeks with effective tetracycline levels released locally over this time period, which achieved good antibacterial activity.