In vitro antibiotic release from poly(3-hydroxybutyrate-co-3-hydroxyvalerate) rods

Provision and maintenance of adequate concentrations of antibiotics at infection sites is very important in treating highly resistant infections. For diseases like implant related osteomyelitis (IRO) it is best to provide this locally via implanted drug formulations, as systemic administration of the antibiotic may not be effective due to damaged vasculature. In this study, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) rods containing 7, 14 and 22% (mol) 3-hydroxyvalerate were loaded with sulbactam:cefoperazone or gentamicin, and their antibiotic release behaviours were studied under in vitro conditions in physiological phosphate buffer at room temperature. The release patterns were representative of release from monolithic devices where a rapid early release phase is followed by a slower and prolonged release. With PHBV 22 rods, the latter phase continued for approximately 2 months. This duration is critical because a proper antibiotic therapy of IRO requires the minimal effective concentration for at least 6 weeks. After in vitro release, voids with sharp edges were detected on the rods, indicating that the drug crystals dissolved but the polymer did not undergo erosion within this test period. Changing the polymer:drug ratio from 2:1 to 20:1 substantially decreased the drug release rate. A change of polymer type, however, did not lead to any detectable changes in the release patterns. Gentamicin release also followed a similar pattern, except that the concentration of the drug in the release medium exhibited a decrease after long release periods, indicating degradation (or decomposition) of the antibiotic in the release medium.