Vancomycin elution and antibacterial activity of medium-viscosity versus medium-high-viscosity antibiotic-loaded bone cement: an in vitro comparative study

Periprosthetic joint infection (PJI) following total joint arthroplasty is a devastating complication often managed with two-stage revision using antibiotic-loaded bone cement (ALBC) spacers. The influence of cement viscosity on antibiotic elution and antibacterial efficacy remains incompletely characterized. This study compared the vancomycin elution profiles and antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) of medium-viscosity versus medium-high-viscosity PMMA cements at three vancomycin loads (2, 4, and 6 g per 40 g cement). Medium-viscosity (Group M) and medium-high-viscosity (Group H) gentamicin-loaded PMMA cements were supplemented with 2, 4, or 6 g of vancomycin (subgroups M2/M4/M6 and H2/H4/H6). Eluates were collected over 84 days, and vancomycin concentrations were quantified by HPLC. Antibacterial activity against planktonic MRSA was assessed using a colony-counting method, and the inhibition rate was calculated relative to a negative control. Vancomycin load was the predominant determinant of both elution kinetics and antibacterial activity, with the 6 g group showing significantly higher cumulative release and inhibition rates than the 4 g and 2 g groups ( P < 0.001 for all comparisons). Cement viscosity did not significantly affect elution concentration or inhibition rate at any time point or any equivalent vancomycin load ( P > 0.05 for all viscosity comparisons). The 4 g formulation exhibited intermediate antibacterial activity (approximately 47% inhibition rate) and a relatively stable elution profile. Under the present in vitro conditions, vancomycin load, rather than cement viscosity, determines elution and antibacterial performance against planktonic MRSA. The 4 g formulation may represent a candidate of interest for further mechanical and in vivo evaluation. However, biofilm resistance and clinical efficacy were not assessed, and these findings should not be interpreted as establishing a clinical optimal formulation.