Elution profiles of tobramycin and vancomycin from high-purity calcium sulphate beads incubated in a range of simulated body fluids

The aim of this study was to characterise the elution profiles of antibiotics in combination with pharmaceutical grade calcium sulphate beads in phosphate buffered saline and other physiological solutions which more closely mimic the invivo environment. Synthetic recrystallised calcium sulphate was combined with vancomycin hydrochloride powder and tobramycin sulphate solution and the paste was formed into 3mm diameter hemispherical beads. Then 2g of beads were immersed in 2ml of either phosphate buffered saline, Dulbecco's Modified Eagle Medium or Hartmann's solution and incubated at 37? for up to 21 days. At a range of time points, eluent was removed for analysis by liquid chromatography-mass spectrometry (LC-MS). Tobramycin sulphate and vancomycin hydrochloride release was successfully quantified against standard curves from solutions eluted in all three physiological media (phosphate buffered saline, Dulbecco's Modified Eagle Medium and Hartmann's solution) during incubation with calcium sulphate beads. One hour eluate concentrations were high, up to 2602 mu g/ml for tobramycin in phosphate buffered saline and 7417 mu g/ml for vancomycin, whereas in DMEM, the levels of tobramycin were 2458 mu g/ml and 4401 mu g/ml for vancomycin. The levels in HRT were 2354 mu g/ml for tobramycin and 5948 mu g/ml for vancomycin. The results show highest levels of antibiotic elution over the first 24h, which gradually diminish over the following 21 days.