Pharmacokinetics of platinum and safety evaluation of carboplatin-impregnated calcium sulfate hemihydrate beads after implantation in healthy cats

Evaluation of bioabsorbable calcium sulfate hemihydrate beads for local delivery of carboplatin

The objectives of this study were to evaluate a novel kit of resorbable calcium sulfate beads marketed specifically for use in veterinary medicine and generally used for local delivery of antimicrobials as carboplatin-delivery system. The study characterized the elution of carboplatin in vitro, and investigated whether the initial dose and formulation of carboplatin, or the bead size significantly influences carboplatin elution in vitro. Calcium sulfate hemihydrate beads of 3- and 5-mm diameter were prepared. Five doses and two formulations of carboplatin (20, 50, 100, and 500 mg carboplatin per kit in powder formulation; 20 mg in liquid formulation) were tested in triplicates for each diameter beads. Beads were placed in 37°C phosphate buffered saline for 72 hours. Carboplatin concentrations in the eluent were measured by high-performance liquid chromatography at 11 time points with a modified United States Pharmacopeia assay. Concentrations of carboplatin in the eluent proportionally increased with the initial dose and peaked between 13 and 52 hours, ranging from 42.1% to 79.3% of the incorporated load. Higher peak concentrations, percentages released, and elution rates were observed with the liquid formulation and with higher carboplatin doses. There was no significant difference in maximum carboplatin concentrations between 3- and 5-mm diameter beads, but 5-mm diameter beads had slower elution rates. The novel kit can be used for preparation of carboplatin-impregnated resorbable calcium sulfate beads at variable doses, sizes and formulations. Further study is warranted to define the in vivo requirements and effective carboplatin dose, spatial diffusion and desired duration of elution.

Repeatability of in vitro carboplatin elution from carboplatin-impregnated calcium sulfate hemihydrate beads made in a clinic setting

OBJECTIVE

To evaluate the intra-lot and inter-lot consistency and total carboplatin elution over 25 days from carboplatin-impregnated calcium sulfate hemihydrate (C-I CSH) beads manufactured in a clinic setting.

STUDY DESIGN

In vitro elution study.

METHODS

Two volumes of carboplatin were mixed with CSH to yield 4 mg and 8 mg C-I CSH doses. Two lots of beads were made for each concentration and split into five doses (n = 10 per concentration). Beads hardened in molds and were placed in a covered six-well plate, submerged in phosphate-buffered saline, and incubated with samples collected at 12 time points (0, 6, 12, and 24 hours and 2, 3, 5, 7, 10, 14, 18, and 25 days). The amount of carboplatin in each sample was evaluated by high-performance liquid chromatography/mass spectrometry. Correction for carboplatin degradation and dilution was applied, and eluted carboplatin was calculated. Intra-lot and inter-lot coefficient of variation (CV) was calculated for each concentration.

RESULTS

The intra-lot CV ranged between 7.9% and 23.1%, and the inter-lot CV ranged from 3.5% to 10.3%, with improvement noted in each successive lot of beads. Mean peak eluted carboplatin was 2.45 ± 0.43 mg (61%) and 3.68 ± 0.41 mg (45.9%) for the 4-mg and 8-mg C-I CSH beads, respectively, with both occurring at the 12-hour timepoint.

CONCLUSION

Progressive improvement in variability with successive lots of beads indicated a learning curve with bead manufacturing with a low variation both within and between lots of C-I CSH beads.

CLINICAL SIGNIFICANCE

On-site mixing of carboplatin with commercial CSH bead powder leads to a low variation of carboplatin per bead dose.