Release Kinetics of Tobramycin Sulfate from Polymethylmethacrylate Implants

Novel microcomposite implant for the controlled delivery of antibiotics in the treatment of osteomyelitis following total joint replacement

The objective of this study was to develop a novel microcomposite implant to be used in the treatment of osteomyelitis following total joint arthroplasty, with the dual purpose of releasing high local concentrations of antibiotic to eradicate the infection while providing adequate mechanical strength to maintain the dynamic or static spacer. Vancomycin-loaded microcomposite implants were fabricated by incorporating drug-loaded microparticles comprised of mesoporous silica into commonly employed polymethylmethacrylate (PMMA) bone cement, to yield a final drug loading of 10% w/w. In vitro release kinetics at 37°C were monitored by reverse-phase high-performance liquid chromatography, and compared to the release kinetics of current therapy implants consisting of drug alone incorporated at 10% w/w directly into PMMA bone cement. Results demonstrated a sevenfold improvement in the elution profile of microcomposite systems over current therapy implants. In vivo delivery of vancomycin to bone from microcomposite implants (70% of payload) was significantly higher than that from current therapy implants (approx. 22% of payload) and maintained significantly higher bone concentrations for up to 2 weeks duration. The elastic modulus showed no statistical difference between microcomposite implants and current standard therapy implants before drug elution, and maintenance of acceptable strength of microcomposite implants postdrug elution. These results demonstrate that we have developed a novel microcomposite spacer that will release continuously high antibiotic concentrations over a prolonged period of time, offering the possibility to eliminate infection and avoid the emergence of new resistant bacterial strains, while maintaining the requisite mechanical properties for proper space maintenance and joint fixation.

Synthesis, Properties, and In Vitro Hydrolytic Degradation of Poly(d,l-lactide-co-glycolide-co-ε-caprolactone)

Random copolymers of poly(d,l-lactide-co-glycolide-co-ε-caprolactone) (PLGC) were synthesized by the ring-opening polymerization of d,l-lactide (DLLA), glycolide (GA), andε-caprolactone (CL). The effects of CL on the copolymers were evaluated to prepare suitable copolymers with controlled properties. Our results showed that the CL content significantly influenced the thermal and mechanical properties of the copolymers and that the CL content in compositions could be altered to control properties of random copolymers. The in vitro hydrolytic degradation of the resulting implants showed that the degradation rate of PLGC was lower than that of PLGA, which could markedly reduce acidic degradation products. Finally, we demonstrated that higher CL contents in compositions slowed degradation rates.

In vitro and in vivo release of ciprofloxacin from PLGA 50:50 implants

Poly(lactides-co-glycolides) [PLGA] are widely investigated biodegradable polymers and are extensively used in several biomaterials applications as well as drug delivery systems. These polymers degrade by bulk hydrolysis of ester bonds and break down into their constituent monomers, lactic and glycolic acids which are excreted from the body. The purpose of this investigation was to develop and characterize a biodegradable, implantable delivery system containing ciprofloxacin hydrochloride (HCl) for the localized treatment of osteomyelitis and to study the extent of drug penetration from the site of implantation into the bone. Osteomyelitis is an inflammatory bone disease caused by pyogenic bacteria and involves the medullary cavity, cortex and periosteum. The advantages of localized biodegradable therapy include high, local antibiotic concentration at the site of infection, as well as, obviation of the need for removal of the implant after treatment. PLGA 50:50 implants were compressed from microcapsules prepared by nonsolvent-induced phase-separation using two solvent-nonsolvent systems, viz., methylene chloride-hexane (non-polar) and acetone-phosphate buffer (polar). In vitro dissolution studies were performed to study the effect of manufacturing procedure, drug loading and pH on the release of ciprofloxacin HCl. The extent of penetration of the drug from the site of implantation was studied using a rabbit model. The results of in vitro studies illustrated that drug release from implants made by the nonpolar method was more rapid as compared to implants made by the polar method. The release of ciprofloxacin HCl. The extent of the penetration of the drug from the site of implantation was studied using a rabbit model. The results of in vitro studies illustrated that drug release from implants made by the nonpolar method was more rapid as compared to implants made by the polar method. The release of ciprofloxacin HCl from the implants was biphasic at < or = 20% w/w drug loading, and monophasic at drug loading levels > or = 35% w/w. In vivo studies indicated that PLGA 50:50 implants were almost completely resorbed within five to six weeks. Sustained drug levels, greater than the minimum inhibitory concentration (MIC) of ciprofloxacin, up to 70 mm from the site of implantation, were detected for a period of six weeks.

Therapeutic applications of implantable drug delivery systems

In the past, drugs were frequently administered orally, as liquids or in powder forms. To avoid problems incurred through the utilization of the oral route of drug administration, new dosage forms containing the drug(s) were introduced. As time progressed, there was a need for delivery systems that could maintain a steady release of drug to the specific site of action. Therefore, drug delivery systems were developed to optimize the therapeutic properties of drug products and render them more safe, effective, and reliable. Implantable drug delivery systems (IDDS) are an example of such systems available for therapeutic use. The application of currently available implantable drug delivery systems is the main focus of this review. IDDS can be classified into three major categories: biodegradable or nonbiodegradable implants, implantable pump systems, and the newest atypical class of implants. Biodegradable and nonbiodegradable implants are available as monolithic systems or reservoir systems. The release kinetics of drugs from such systems depend on both the solubility and diffusion coefficient of the drug in the polymer, the drug load, as well as the in vivo degradation rate of the polymer, especially, in the case of the biodegradable systems. Controlled release of drug from the implantable pump is generally achieved utilizing the microtechnology of electronic systems and remote-controlled flow rate manipulation through the maintenance of a constant pressure difference. The third atypical class includes those which have been recently developed such as ceramic hydroxyapatite antibiotic systems used in the treatment of bone infections, intraocular implants for the treatment of glaucoma, and transurethral implants utilized in the treatment of impotence. The major advantages of these systems include targeted local delivery of drugs at a constant rate, less drug required to treat the disease state, minimization of possible side effects, and enhanced efficacy of treatment. Also, these forms of delivery systems are capable of protecting drugs which are unstable in vivo and that would normally require a frequent dosing intervals. Due to the development of such sustained release formulations, it is now possible to administer unstable drugs once a week to once a year that in the past required frequent daily dosing. Preliminary studies using these systems have shown superior effectiveness over conventional methods of treatment. However, one limitation of these newly developed drug delivery systems is the fact that their cost-to-benefit ratio (cost/benefit) is too high which restricts their use over conventional dosage forms. Hopefully, in the future, new implantable systems can be developed at a lower cost, thereby minimizing the cost-to-benefit ratio and therefore, be used extensively in standard therapeutic practice. Some of the most recently discovered implants are in the early developmental stages and more rigorous clinical testing is required prior to their use in standard practice.

Comparison of new and existing spectrophotometric methods for the analysis of tobramycin and other aminoglycosides

New indirect spectrophotometric methods of analysis of tobramycin using the derivatizing agents o-phthaldialdehyde, fluorescamine, and dansyl chloride were developed and compared with existing methods. Optimum reaction conditions were established for the complex formation between tobramycin and each reagent. The sensitivity and reproducibility of these new procedures were compared with results obtained using published methods. Of the new methods, the o-phthaldialdehyde and fluorescamine procedures were more sensitive and reproducible than the dansyl chloride procedure. Further, these procedures were subsequently applied to the analysis of aqueous solutions of other aminoglycosides including amikacin, neomycin, gentamicin, and kanamycin.