[Microbial and pharmacological characteristics of VancogenX].

PURPOSE OF THE STUDY

Prosthetic joint infection is a feared complication in total hip arthroplasty. The use of antibiotic-impregnated bone cement is the important part of preventive and therapeutic strategies. At present a number of commercial bone cements are available and support of their use by the results of experimental trials and clinical studies has varied. In relation to this issue we studied essential microbiological and pharmacological characteristics of VancogenX in comparison with gentamicin-loaded bone cement used conventionally.

MATERIAL AND METHODS

Based on a previously described protocol, we tested pellets of four commercial bone cements, namely, Hi-Fatigue G, Palacos R+G, VancogenX, and Palacos R as a control. Bone cement was prepared in a vacuum-mixing system. The strains used for bacterial load included Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Pseudomonas aeruginosa and Escherichia coli. Each cement was tested for its antimicrobial and antibiofilm activities and the results were evaluated by standard methods. In addition, we investigated time-related release of gentamicin and vancomycin from the bone cements tested.

RESULTS

All antibiotic-loaded cement pellets were able to prevent growth of the bacterial strains tested. The bactericidal effect lasted for several days in relation to the bacterial species and cement used, with the exception of S. epidermidis whose growth was inhibited by gentamicin-loaded cement only for one day. The antibiotic-loaded pellets also prevented the formation of a biofilm for 24 hours at least. The major amount of vancomycin (32.915 mg/l) was released from VancogenX to MH medium within 24 hours and the last measureable amount (4.327 mg/l) was recorded at 48 hours after the start of the experiment. In physiological saline the highest level of vancomycin was 139.852 mg/ml measured at 24 hours, and the antibiotic was detectable at a level of 2.334 mg/ml as late as 8 days after the experiment started. Release of gentamicin from VancogenX was as follows: the 24-hour level was higher in MH medium than physiological saline (178 versus 131.4 mg/ml); however, gentamicin was still detectable in physiological saline at 192 hours after the start of the experiment while no gentamicin was found in MH medium after 72 hours.

DISCUSSION

The antimicrobial effect of VancogenX bone cement was not an unexpected finding since both gentamicin and vancomycin have been used with bone cement for a long time and their combination is optimal in terms of preventing prosthetic joint infection. However, there is a disputable issue of poor release of vancomycin from bone cement. In MH medium we were able to detect the vancomycin released from VancogenX only for two days after the initial rapid elution while its release into physiological saline seemed to be slower but much longer. It is possible that more vancomycin is released from bone cement, but this amount is immediately bound to proteins in the cement vicinity and this process is not detectable by any analytical method.

CONCLUSIONS

The bone cement VancogenX showed excellent antimicrobial and antibiofilm properties and can be recommended for use in orthopaedic practice. Therapy of prosthetic joint infection is the main indication. Extension of the indication to the prevention of prosthetic joint infection in high-risk patients should be preceded by biomechanical studies demonstrating that the cement is appropriate for long-term implant fixation.