Skeletal Tissue Engineering Group Amsterdam (STEGA), Department of Orthopaedic Surgery, VU Medical Center, 1007 MB Amsterdam, The Netherlands
Keywords: antibiotic combinations , antibiotic-loaded cement , drug delivery systems , surgical wound infections , topical administration
Sir,
A recent article by Bertazzoni Minelli et al.1 proposes new treatment options for the increasing problem of implant infection caused by resistant strains and describes the release of gentamicin and vancomycin from poly-methyl-methacrylate (PMMA) spacers.
However, their interpretation that a high clinical response rate would support the clinical potential of these devices seems to overlook several factors. (i) The small number of positive pre-operative cultures (nine of the 20 patients treated), and the lack of specificity of blood-tests and radiographs2 undermine the clinical evidence of infection that was stated by the authors. (ii) The effect of local treatment with the spacers is obscured by concomitant antibiotic treatment in all patients, because a combination of parenteral and oral therapy may result in a 8491% success rate.3 (iii) The low combined antibiotic release (0.2 mg/g) does not meet the minimal release requirements (2 mg/g) described by Kühn4 and might ultimately induce resistant strains.5 The higher release reported from antibiotic beads and biodegradable carriers (up to 90%) would favour these treatment modalities over spacers.6,7
The release pattern describedhigh initial followed by low, but constant releaseis not clearly apparent from the in vitro data. (i) Only one control spacer was included per antibiotic groupassuming a low sample variationcontrariwise, the removed spacers seem to indicate a large initial variation in antibiotic release. (ii) Measurements after 72 and 240 h were extrapolated to allow addition of seven datapoints to the existing three. This gives the impression of a constant release from 96 to 240 h and possibly masks elution of subinhibitory antibiotic quantities during later stages of this interval. Therefore, the conclusions on similar kinetics of removed and control spacers, and on constant release kinetics after 24 h appear preliminary.
Additionally, the choice of last-resort antibiotics in these patients appears in contradiction with the expressed concern for the emerging problem of antibiotic resistance and does not seem to comply with recommendations for orthopaedic surgeons.8
To conclude, the additional effect of antibiotic-containing spacers remains unproven and the release pattern was incompletely characterized. Therefore, the low antibiotic release reported in this study would indicate preferential use of established treatment modalities such as PMMA beads or antibiotic-containing fleeces.7
Footnotes
* Corresponding author. Tel: +31-20-4442355; Fax: +31-20-4442357; Email: h.stallmann{at}vumc.nl
References
1
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Bertazzoni Minelli, E., Benini, A., Magnan, B. et al. (2004). Release of gentamicin and vancomycin from temporary human hip spacers in two-stage revision of infected arthroplasty. Journal of Antimicrobial Chemotherapy 53, 32934.
2 . Garvin, K. L., Luck, J. V., Rupp, M. E. et al. (2000). Infections in orthopaedics. In Orthopaedic Basic Science, 2nd edn (Buckwalter, J. A., Einhorn, T. A. & Simon, S. R., Eds), pp. 23959. American Academy of Orthopaedic Surgeons, Rosemont, IL, USA.
3 . Mader, J. T., Wang, J. & Calhoun, J. H. (2002). Antibiotic therapy for musculoskeletal infections. Instructional Course Lectures 51, 53951.
4 . Kühn, K. D. (2000). Bone Cements: Up-to-Date Comparison of Physical and Chemical Properties of Commercial Materials. Springer, London, UK.
5 . van de Belt, H., Neut, D., van Horn, J. R. et al. (1999). Antibiotic resistance to treat or not to treat? Nature Medicine 5, 3589.[CrossRef]
6 . Walenkamp, G. (1989). Small PMMA beads improve gentamicin release. Acta Orthopaedica Scandinavica 60, 6689.
7 . Walenkamp, G. H. (2001). Gentamicin PMMA beads and other local antibiotic carriers in two-stage revision of total knee infection: a review. Journal of Chemotherapy 13, 6672.[ISI]
8 . Osmon, D. R. (2002). Antimicrobial resistance: guidelines for the practicing orthopaedic surgeon. Instructional Course Lectures 51, 52737.
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