Another factor influencing elution rates is the shape of the beads. These are not commercially available and must be made by the veterinarian. They may be made at the time of surgery aseptically and implanted immediately or made preoperative, sterilized with ethylene oxide, and stored for future use. The shelf life for these beads is unknown but assumed to be the normal expiration date of the antibiotic. Because the fumes are annoying and potentially damaging to contact lenses, many prefer to make the beads in a hood prior to surgery.
Any unused beads are gas sterilized and used in future patients.
With some antibiotics this several minutes. Once the polymerization begins, the cement hardens within 10 minutes. Refrigerating the reagents prior to use will extend this time. It can be challenging to make all the beads that quickly and the aid of an assistant is very helpful. Beads may be rolled into spheres and strung on a fine gauge wife.