Assessment of the differences in pharmacokinetics and pharmacodynamics between four distinct formulations of triamcinolone acetonide.

PURPOSE: To compare the durability of Kenalog, Trivaris, Triesence, and compounding pharmacy preservative-free triamcinolone acetonide in pigmented rabbits with syneretic vitreous using direct visualization, pharmacodynamics, and pharmacokinetics. METHODS: Twenty-five Dutch-belted rabbits were used. Pharmacokinetic experiment: Rabbits were intravitreally injected with one of four 4-mg triamcinolone acetonide formulations. Wide-field imaging was serially performed to document residual drug mass. Pharmacodynamics experiment: Four triamcinolone acetonide groups and one control group received intravitreal recombinant human vascular endothelial growth factor 165 every 2 weeks and were followed with fluorescein angiography to assess vascular endothelial growth factor retinal vasculopathy as a measure of residual steroid effect. Particle size of the formulations was measured with Mastersizer 2000. RESULTS: Remaining triamcinolone acetonide mass after 19 weeks: 12,091 ± 2,512 pixels for the Kenalog group, 1,307.36 ± 695.57 for Trivaris, 5577 ± 1477 for Triesence, and 1,535 ± 329 for compounded preservative-free triamcinolone acetonide. Kenalog suppressed recombinant human vascular endothelial growth factor-induced retinopathy more effectively than the other triamcinolone acetonide groups at Week 39, the final time point assessed. Particle size (90th percentile) was 47 µm for Kenalog, 26 µm for Triesence, and 22 µm for both compounded preservative-free triamcinolone acetonide and Trivaris. CONCLUSION: Triamcinolone acetonide formulations do not have the same pharmacokinetics/pharmacodynamics. Kenalog has the longest vitreous visibility and durability. Particle size appears to correlate with efficacy and durability.

Efficacy and safety of memantine treatment for reduction of changes associated with experimental glaucoma in monkey, II: Structural measures.

PURPOSE: To determine, using anatomic measurements, whether daily oral dosing with memantine is both safe and effective to reduce the injury associated with experimental glaucoma in primates. METHODS: Argon laser treatment of the anterior chamber angle was used to induce chronic ocular hypertension (COHT) in the right eyes of 18 macaque monkeys. Nine animals were daily orally dosed with 4 mg/kg memantine while the other nine animals received vehicle only. Measurements of intraocular pressure (IOP) from both eyes of all animals were made at regular intervals. Appearance of the optic nerve head, retinal vessels, and surrounding retina was documented with stereo fundus photographs obtained at multiple time points throughout the study. Measurements of optic nerve head topography were obtained from confocal laser scans made from animals with the highest IOPs at approximately 3, 5, and 10 months after elevation of IOP. At approximately 16 months after IOP elevation, animals were killed and histologic counts of cells in the retinal ganglion cell (RGC) layer were made. RESULTS: Histologic measurements showed that, for animals with moderate elevation of IOP, memantine treatment was associated with an enhanced survival of RGCs in the inferior retina. Measurements of optic nerve head topography showed less IOP-induced change in memantine-treated animals. This effect was seen in measurements of both the cup and the neuroretinal rim. A comparison of these same histologic and morphologic measurements in normotensive eyes from the two treatment groups showed that memantine treatment was not associated with any significant effects on these eyes. CONCLUSIONS: Histologic measurements of RGC survival as well as tomographic measurements of nerve head topography show that systemic treatment with memantine, a compound which does not lower intraocular pressure, is both safe and effective to reduce changes associated with experimental glaucoma.