Antibiofilm Activity of a Novel Calcium Phosphate Cement Doped with Two Antibiotics

This study presents the development of a degradable and biocompatible calcium phosphate cement (CPC) co-loaded with gentamicin (1.25 wt%) and vancomycin (4.25 wt%) for the local treatment of polymicrobial bone infections. The antibiotics were incorporated-individually or in combination-into the solid phase of Graftys^® Quickset (GQS), an injectable CPC. Antibiotic loading modifies some of the intrinsic properties of the GQS cement. Porosity exceeded 53%, compressive strength reduced around 5 MPa, which is comparable to calcium sulphates cements, and the setting time, although extended, remained within the clinically acceptable threshold (<20 min), ensuring suitable handling. A burst release of both antibiotics was observed within the first 24 h, with sustained release over time and no cytotoxic effects on human osteoblasts. The dual-loaded cement exhibited broad-spectrum antibacterial activity against both Gram-positive and Gram-negative strains, including methicillin-resistant isolates, in both planktonic and biofilm forms. Notably, the combination of both antibiotics demonstrated superior efficacy compared to either antibiotic alone. These findings suggest that this dual-antibiotic-loaded CPC offers a promising strategy for localised treatment of complex bone infections such as osteomyelitis, where polymicrobial involvement and antibiotic resistance pose significant therapeutic challenges.