ELUTION OF GENTAMICIN AND VANCOMYCIN FROM ACRYLIC BONE CEMENT: AN IN VITRO STUDY

Abstract

The use of polymethylmethacrylate (PMMA) bone cement loaded with antibiotics has become increasingly common in orthopaedic surgery. However, bacterial resistance in antibiotics is an increasing and emerging problem. PMMA bone cements containing different antibiotics, such as gentamicin plus vancomycin may be effective in prevention and treatment of infections (particularly from MRSA and MRSE).

The purpose of this study was to determine the in vitro elution characteristics of gentamicin and vancomycin when combined in acrylic cement.

Three groups of ten cement disks were prepared. Group I (control group) contained 0.5g of gentamicin per 40-g packet of Palacos-R+G powder. Group II contained 0.5g of gentamicin and 1g of powdered vancomycin and group III contained 0.5g of gentamicin and aqueous solution of vancomycin. Each cement disc (25mm x 20mm) was immersed in a 50-mL bath of normal saline at 37oC. Samples were taken at specific sampling intervals (1, 3, 7, 15, 30, 60, 90, 120, 150, 180 days). Antibiotic concentrations were measured using fluorescence polarisation immunoassay.

With regards to gentamicin release, high but rapidly decreasing antibiotic levels were detected within the first week and low concentration after the first month. Samples from Group II eluted significantly more gentamicin (120%–20% during the first month). The influence on the gentamicin release was significant but minor when aqueous solution of vancomycin (Group III) was added. With regards to vancomycin release, high antibiotic levels were detected within the first 3 days and low concentrations after the first week. Cement samples from Group II eluted significantly more antibiotic in comparison with samples from Group III.

Bone cements loaded with combinations of gentamicin and vancomycin are more effective in releasing gentamicin than bone cements with gentamicin as a single drug. Powdered vancomycin in cement samples has better elution characteristics in comparison with aqueous solution of vancomycin.