Phenolphthalein used to assess permeability of antibiotic-laden polymethylmethacrylate: a pilot study

Elution of antibiotics from polymethylmethacrylate laden with antibiotics is dependent on the permeability of the polymethylmethacrylate. Increasing polymethylmethacrylate permeability by adding fillers has been suggested to increase antibiotic elution but the resulting increase in permeability has not been assessed directly. A simple method to assess polymethylmethacrylate permeability is proposed. Phenolphthalein was added to the polymethylmethacrylate to indicate the level of penetration of fluid with pH of 10.3. Glycine in three different amounts (0.45 g, 7 g, and 28 g) or a combination of antibiotics (13.6 g) was added as a filler to increase the permeability. Beads of each mixture were made and soaked in fluid with a pH of 10.3. An immediate intense magenta coloration occurred on contact of the beads with the fluid. A zone of magenta was seen to penetrate into the depths of polymethylmethacrylate beads. That penetration increased with the amount of the filler and with time in the fluid bath. The type of filler material also affected the rate of fluid penetration. Permeability of various antibiotic polymethylmethacrylate mixtures can be determined qualitatively using this method. The observations may be useful to determine which mixtures warrant more expensive antibiotic elution studies.