Abstract: BACKGROUND: For diabetic foot infections, traditional vancomycin-loaded bone cement has a limited antibacterial spectrum, and there is an urgent need for novel drug carriers.
OBJECTIVE: To explore the in vitro elution characteristics of polymyxin B sulfate-loaded bone cement. 
METHODS: Polymyxin B sulfate powder was uniformly mixed with polymethyl methacrylate bone cement and poured into molds to prepare bone cement microspheres with diameters of 5 and 7 mm. The two types of bone cement microspheres of different diameters were immersed in 1 mL of PBS, and elution samples were collected at specific time points. The concentration of polymyxin B sulfate in the eluent was determined by mass spectrometry, and the drug release pattern was analyzed. 
RESULTS AND CONCLUSION: (1) The drug release peaks for both types of bone cement microspheres occurred between 0 and 0.5 h, after which the release rate gradually decreased. Inter-group comparison showed that the drug release rate and cumulative release rate of the 5 mm diameter microspheres were higher than those of the 7 mm diameter microspheres. The cumulative drug release rates at 14 days for the 5 mm and 7 mm diameter microspheres were 5.08% and 3.37%, respectively. The drug release from both types of bone cement microspheres of different diameters reached 90% of the total release within 7 days, approaching the release endpoint. The in vitro drug release curves of both types of microspheres conformed to the Ritger-Peppas model (R2=0.998 56, 0.990 90), mainly driven by Fickian diffusion. (2) Polymyxin B sulfate-loaded bone cement exhibits certain sustained-release characteristics, with drug release mainly concentrated in the first 7 days, and low release in the later stages. Therefore, 5-7 days after implantation of polymyxin B bone cement is the optimal time for secondary debridement. Continued placement carries a higher risk of inducing bacterial resistance. The drug release rate is related to the size of the bone cement. In clinical applications, 5 mm diameter microspheres should be considered first to balance the needs for rapid drug release and long-lasting antibacterial effect.

Key words: polymyxin B sulfate, bone cement, bone cement microspheres, antibiotics, in vitro, drug release, diabetic foot infection