Mitomycin C dissolved in a reversible thermosetting gel: target tissue concentrations in the rabbit eye

In vitro release of mitomycin C from collagen implants

PURPOSE

To study Mitomycin C Loaded Collagen Implant (CI) pharmacokinetics behaviour in vitro.

METHODS

The CI were incubated for 15 minutes in different MMC loading solutions with the following concentrations: 0.03 mg/mL (n = 9), 0.3 mg/mL (n = 10) and 3.0 mg/mL (n = 10). The loaded CI were transferred in 100 micro L of 0.9% NaCl. Aqueous flow of 5 micro L/min was simulated. The MMC concentrations of the samples were determined by high performance liquid chromatography (HPLC). Dissolution kinetics were evaluated by a first-order process. The half-life of dissolution and the time of 95% dissolution were determined.

RESULTS

The CI absorbed on average a MMC dose of 0.054, 0.530 and 6.090 micro g when incubated in the different MMC loading solutions containing 0.03 mg/mL, 0.3 mg/mL, 3.0 mg/mL of MMC, respectively. In the release experiments, the mean total dose delivered by CI was 0.0493, 0.585 and 5.291 micro g. A linear correlation between loading concentration and the estimated total dose released was demonstrated. The kinetic parameters showed a fast MMC dissolution. The half-life of the 3 series was 8.8, 10.1 and 10.5 min.

CONCLUSIONS

Commercially available CI can be loaded with MMC, and could provide relatively slower release than sponge delivery of MMC. Clinical implications of these results warrants further studies.

Intrascleral concentration vs depth profile of mitomycin-C after episcleral application: impact of irrigation

Mitomycin-C has been reported to cause toxic effects on the ciliary body after episcleral application during glaucoma surgery. We investigated the intrascleral diffusion of mitomycin-C in an experimental model. The episcleral sides of scleral quadrants of 14 human donor eyes were exposed for 5 min to sponges (corneal light shield, Merocel corp., Mystic, CT, U.S.A.) soaked with 200 microg ml(-1)mitomycin-C. After the exposure one of four quadrants was not irrigated and the episcleral sides of three quadrants were irrigated with 40, 100 and 200 ml saline. A 9 mm scleral disk was punched out with a trephine and frozen on a kryotome plate 2 min after the end of mitomycin-C exposure. An 8 mm diameter scleral disk was then cut with a trephine, again frozen on a kryotome plate and then horizontally dissected with a kryotome. For analysis purposes seven cuts of 20 microm thickness were combined to one layer of 140 microm. Six layers could be reproduced and were analysed. The mitomycin-C concentrations of these layers were analysed by high-performance liquid chromatography. A concentration vs depth profile was calculated for each group, and the half-width of concentration was calculated by log-linear regression. The mitomycin-C concentration of layer 1 was 24.51 microg g(-1)(+/-7.52) without irrigation, 13.15 microg g(-1)(+/-4.38) after 40 ml irrigation, 10.29 (+/-3.53) after 100 ml irrigation and 8.4 microg g(-1)(+/-1.62) after 200 ml irrigation. In layers 1-3 the concentration of mitomycin-C was significantly reduced by irrigation (ANOVA). In the deeper intrascleral layers irrigation had no effect on the mitomycin-C concentrations. Between layers 2 and 6 the half-width of the mitomycin-C concentration was 101 microm (no-irrigation group), 141 microm (40 ml irrigation group), 153 microm (100 ml irrigation group), and 164 microm (200 ml irrigation group). Irrigation reduced the mitomycin-C concentration only down to half of the scleral thickness, leaving the deep intrascleral concentrations unchanged.