Mixture (admixture) of PMMA antibiotic beads in the diabetic foot

We frequently get questions regarding the mixture of absorbable (calcium sulfate or phosphate pellets). The video recipe which we provided on this blog. However, let’s cover the recipe for mixture of polymethyl metharylate.

Similar to our video of absorbable beads, Valerie Schade and Tom Roukis have an absolutely superb video description of the mixture here. Furthermore, we found a detailed recipe and instructions from our veterinary surgery colleagues, which we modify for our use below:
Choice of antibiotic

  • Tobramycin (2.4g– two vials), Amikacin, Gentamicin or Clindamycin can be mixed at 2 g per 20 g PMMA.
  • Vancomycin can also be mixed at 1g
  • One may mix one vial of methylene blue to get additional antifungal/anti S. epidermidis coverage

Preparation of beads

  • Make sure all equipment is ready, as the time available once the powdered polymer and liquid monomer have been mixed is limited.
  • In terms of timing your mixture, note that the aminoglycosides (Tobra, et al) tend to be retardants and the glycopeptides (Vancomycin, et al) tend to be accelerants.
  • Maintain aseptic conditions throughout preparation.
  • Personnel should scrub up before starting preparation.
  • Note that the cement sets in about 15 minutes once mixed, therefore rapid production is important. . Vancomycin tends to promote more rapid setting.
    • Chill the materials, by refrigeration prior to mixing, to prolong setting time.
  • In the sterile bowl, using a sterile spatula, thoroughly mix the antibiotic powder with the polymethylmethacrylate (PMMA) powder.
    • Usually mix 1.0 – 2.0 g antibiotic with 40 – 60 g PMMA powder.
    • A mixture of 1.0 – 2.0 g antibiotic with 20 g PMMA powder has been used.
    • Maximum of 1:5 antibiotic powder to PMMA powder; the cement will not harden properly if more antibiotic powder is used.
    • If liquid antibiotic is used, the hardness of the final cement is reduced.
  • Add the liquid monomer and mix well to a smooth, even consistency.
    • Normally mix at 2:1 powdered PMMA to liquid monomer; a 3:1 ratio may be preferable since it reaches a temperature of about 65 °C maximum compared with 75 °C maximum for the 2:1 mix
  • Place the semi-solid mixture into a 20 mL syringe.
  • Gently expel the mixture onto a sterile surface, in several lines.
    • Expel the cement fairly quickly for larger diameter beads.
    • Stretch the line while expelling the cement for smaller diameter beads.
  • Use a blade to cut the line of cement (still at the malleable stage) into small pieces.
  • Roll the cement pieces into beads.

Storing beads

  • Sort the beads by size.
  • Place the beads in sterile containers.
  • Label each container with the date of construction of the beads, the type and strength of antibiotic and the expiration date of the antibiotic.
  • Preferably gas sterilise (ethylene oxide) the beads prior to use.
    • This may not be needed if strict aseptic technique has been used in production, storage, and removal of beads from their storage container.
    • If sterilising with ethylene oxide, leave to aerate for 24 hours prior to use to be sure the gas has dissipated.]
    • Note: antibiotic potency may be decreased if beads are autoclaved.
Elution characteristics:
We include this diagram from Klemm, and coworkers (2001), which outlines and graphs the antibiotic elution properties of aminoglycoside-admixed PMMA specifically (see figure 2, below).
Here is another terrific link:

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