Microbiological inhibitory characteristics of antibiotic laden cement sticks: An in-vitro study.

This study determines the inhibitory characteristics of three separate formulations of antibiotics in bone cement (Vancomycin, Gentamicin, Vancomycin-Fucidin) on three of the most common organisms found in patients with periprosthetic joint infections around the hip and knee in our center, namely S. epidermidis, S. aureus, and Enterococcus faecalis. The antibiotics were added in their powder form into the bone cement and cement molds created via hand mixing in a sterile environment. Formulation A consisted of 3 grams ofvancomycin in CMW3plain bone cement. Formulation B contained CMW 3 bone cement with preloaded gentamicin. Formulation C contained 3 grams each of vancomycin and 3 grams Fucidin. A negative control was created using plain bone cement without antibiotics. All cements with their respective formulations were placed in individual identical containers with a 5 ml saline bath. Standard solutions of the formulations were created from their respective stock solutions with dosages ranging from 0.625ug/ml to 20 ug/ml. Organisms were mixed into the agar at a quantity of 1 x 106 cells/ml per organism per plate. All experiments were done in triplicate. The inhibitory characteristics were measured as the zone of inhibition (in mm) observed for every period of sampling which was daily for the first week, weekly for the first month and then monthly thereafter, covering a period of 1 year. Vancomycin-Fucidin combination displayed a significant difference in its inhibitory characteristics when compared to the other formulations tested on S. epidermidis and S. aureus. (p-value: < 0.001) Comparison ofvancomycin alone and the combination of vancomycin and Fucidin detected no significant difference across the range of sampling times for E. faecalis (p-value: < 0.001). Gentamicin displayed negligible inhibition on plates with S. aureus and E. faecalis. Inhibition on plates with S. epidermidis was noted but was the least among the three formulations. The combination of Vancomycin-Fucidin demonstrated good inhibitory characteristics on all organisms tested based on our study. Significant elution levels and concentration was observed during the entire sampling period.