JAC Advance Access published online on January 3, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkm491
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In vitro cell compatibility and antibacterial activity of microencapsulated doxycycline designed for improved localized therapy of septic arthritis
1 AO Research Institute, 7270 Davos-Platz, Switzerland 2 Institute of Animal Pathology, Vetsuisse-Faculty, 3001 Berne, Switzerland 3 Clinic for Ruminants, Vetsuisse-Faculty, 3001 Berne, Switzerland 4 Institute of Veterinary Bacteriology, Vetsuisse-Faculty, 8057 Zurich, Switzerland 5 Institute of Pharmaceutical Sciences, ETH Zurich, 8093 Zurich, Switzerland
Received 22 June 2007; returned 16 August 2007; revised 25 September 2007; accepted 23 November 2007
* Corresponding author. Tel: +4144 6326944; Fax: +4144 6321128; E-mail: christina-haerdi{at}ethz.ch
Objectives: For the treatment of septic arthritis in large animals, the local application of antibiotics as a slow release system may be an appropriate means to reach high local bioactivity and low systemic side effects and drug residues. In this study, doxycycline microspheres were developed and tested in vitro for their drug-release properties, suitability for intra-articular application and antimicrobial activity.
Methods: The development of a slow release system was achieved by microencapsulation of the drug into poly(lactide-co-glycolide) microspheres by a novel ultrasonic atomization method. Drug elution was evaluated from microspheres dispersed in elution medium at pre-defined time points by HPLC. Joint-tissue compatibility was tested on cultured bovine synoviocytes by evaluating the expression of pro-inflammatory cytokine mRNA and the production of nitric oxide (NO). Finally, the antimicrobial activity of the released antibiotic was assessed with Gram-negative and Gram-positive bacteria exposed to release medium sampled at days 1, 7 and 12 after microsphere suspension.
Results: An adequate size of the microspheres, sufficient stabilization of doxycycline in aqueous environment and drug release (25 mg microspheres in 4 mL medium) above MIC for bacteria usually isolated in bovine and equine joints were obtained over 15 days. Although the cytokine mRNA expression reflected the excellent tissue compatibility, the results with NO yielded contradictory results. Antimicrobial tests of the release medium proved to match perfectly the activity of non-encapsulated, free doxycycline as reported in the literature.
Conclusions: The newly developed doxycycline delivery system achieved the target specifications and is ready for in vivo testing.
Key Words: septic arthritis , microspheres , in vitro toxicity , antimicrobial activity