Gentamicin loading of calcium phosphate implants: implications for cranioplasty

BACKGROUND: Surgical site infections (SSI) are a significant risk in cranioplasty, with reported rates of around 8–9%. The most common bacteria associated with these nosocomial infections are of the Staphylococcus species, which have the ability to form biofilm. The possibility to deliver antibiotics, such as gentamicin, locally rather than systemically could potentially lower the early postoperative SSI. Various antibiotic dosages are being applied clinically, without any true consensus on the effectiveness. METHODS: Drug release from calcium phosphate (CaP), polyetheretherketone (PEEK), and titanium (Ti) samples was evaluated. Microbiological studies with Staphylococcus aureus (SA) and Staphylococcus epidermidis (SE) including strains from clinical infection were used to establish clinically relevant concentrations. RESULTS: The CaP samples were able to retain and release gentamicin overtime, whereas the Ti and PEEK samples did not show any drug uptake or release. A gentamicin loading concentration of 400 μg/ml was shown to be effective in in vitro microbiological studies with both SA and SE. CONCLUSIONS: Out of the three materials studied, only CaP could be loaded with gentamicin. An initial loading concentration of 400 μg/ml appears to establish an effective gentamicin concentration, possibly translating into a clinical benefit in cranioplasty.