Intravitreal pharmacokinetics and retinal concentrations of ganciclovir and foscarnet after intravitreal administration in rabbits.

PURPOSE: To perform a detailed pharmacokinetic study and to evaluate the drug levels reached in the retina after the intravitreal administration of ganciclovir and foscarnet to rabbits. METHODS: Retinal and vitreal levels of both drugs were measured by high-performance liquid chromatography at 1, 6, 12, 24, 36, 48, 60, and 72 hours after a single intravitreal injection of 196 microg and 800 microg of ganciclovir and 960 microg of foscarnet to three groups of 24 pigmented rabbits. A noncompartmental pharmacokinetic analysis was used. RESULTS: Both drugs incorporated rapidly into the retina, but no equilibrium was observed between the drug levels in the vitreous humor and retina. Mean ganciclovir levels in vitreous and retina were 179.6 microg/g and 131.3 microg/g (dose of 196 microg), 755.7 microg/g and 381.6 microg/g (dose of 800 microg) at 1 hour after administration, decreasing to 0.1 microg/g, 0.6 microg/g, 0.8 microg/g, and 0.7 microg/g, respectively, by 72 hours. Mean foscarnet levels in vitreous and retina were 944 microg/g and 217.1 microg/g at 1 hour after administration, decreasing to 74 microg/g and 17.1 microg/g, respectively, by 72 hours. Whereas both doses of ganciclovir yielded retinal levels above the mean inhibitory concentration (IC50) of most human cytomegalovirus (CMV) isolates for more than 60 hours, foscarnet retinal levels were lower than the CMV IC50 before 36 hours had elapsed after administration. CONCLUSIONS: The results suggest that the intravitreal administration of ganciclovir has a better pharmacokinetic profile than foscarnet for the treatment of retinitis caused by CMV and other herpes viruses and support the administration of intravitreal ganciclovir twice a week as a treatment for CMV retinitis.

Extramedullary plasmacytoma of the orbit.

PURPOSE: To report a case of extramedullary plasmacytoma of the orbit. METHODS: A 71-year-old patient presented with diplopia eyelid fullness and limitation of ocular motility in the left eye. Visual acuity was counting fingers, intraocular pressure 34 mmHg and fundus eye examination showed choroidal folds in the involved eye. RESULTS: CT scan showed a mass filling the superior and external left orbit without bone destruction. A biopsy was performed revealing that the tumour was composed of plasmacytoid cells positive with immunohistochemical stains for Kappa light chains and epithelial membrane antigen. Systemic work up was negative. The diagnosis of extramedullary orbital plasmacytoma was made. The patient was treated with external beam radiotherapy (40 Gy) and has remained disease free for four years (49 months). CONCLUSION: Extramedullary plasmacytomas of the orbit are extremely rare tumours. Accurate and early diagnosis is essential for the therapeutic approach. Extensive medical work up to rule out multiple myeloma or other malignant lymphoproliferative conditions involving the orbit is needed when the diagnosis of orbital extramedullary plasmacytoma is suspected because treatment and prognosis are very different.