In vitro evaluation of antibiotic elution from polymethylmethacrylate (PMMA) and mechanical assessment of antibiotic-PMMA composites

Objective-To determine whether different methods of sterilization of antibi otic vials or the heat of polymerization altered the antimicrobial activity or mechanical properties of antibiotic/polymethyl-methacrylate (PMMA) comp osites when compared to antibiotic-free PMMA. Study Design-In vitro study. Methods-Steam-sterilized, gas-sterilized, and non-sterilized 1 gram vials o f cefazolin and injectable gentamicin sulfate (high and low doses) were mix ed with PMMA to prepare composites for antibiotic elution evaluation, compr ession, and elongation testing. Blocks of PMMA that contained antibiotic we re assayed for antibacterial activity using an agar gel diffusion method or were placed in phosphate buffered saline (PBS) to assess elution of antibi otic. Phosphate buffered saline samples from steam-sterilized cefazolin and high-dose gentamicin groups were assayed on days 1, 2, 5, and 9 for cefazo lin or gentamicin concentration by high-pressure liquid chromatography or f luorescent polarization immunoassay, respectively. Results-PMMA blocks containing antibiotic inhibited bacterial growth of Sta phylococus aureus 25923 for an average of 9 days. Cefazolin and gentamicin concentration in PBS decreased dramatically after the first 24 hours, but r emained above minimum inhibitory concentration (MIC) throughout the experim ent for all groups except low-dose gentamicin. Compressive strength of plug s made from plain cement and plugs made from PMMA mixed with untreated and steam-sterilized cefazolin was similar, but was significantly different fro m the other groups. There appeared to be an inverse relationship between co mpressive strength and elongation. Conclusion-PMMA/antibiotic composites inhibited bacterial growth for 7 to 1 0 days. Compressive strength was affected by different additions of antibio tic. Clinical Relevance-Bacteria introduced during a surgical procedure may be i nhibited by elution of antibiotic from PMMA at the time of contamination. ( C) Copyright 2000 by The American College of Veterinary Surgeons.