Purpose: To examine the decrease in the intraocular concentration of intravitreally injected triamcinolone acetonide over an 8-month period in a rabbit model.
Design: Experimental study.
Participants: The study included 18 white New Zealand rabbits.
Methods: The animals received an intravitreal injection of 6 mg triamcinolone acetonide. Vitreous and aqueous humor samples of the anterior and posterior chamber were taken at the first and third day, at 1 and 2 weeks, and at 1, 1.5, 2, 3, 6, and 8 months. The concentrations of triamcinolone were analyzed using a high-phase liquid chromatography assay.
Main outcome measures: Intraocular concentration of triamcinolone during follow-up.
Results: Over the entire study period, triamcinolone concentrations were significantly higher in the vitreous samples than in the anterior chamber samples (day 1, 14 434+/-10 768 microg/l vs. 21.0+/-18.9 microg/l; day 30, 571.3+/-329.6 microg/l vs. 6.1+/-1.6 microg/l; month 8, 70.7+/-37.0 microg/l vs. 3.3+/-1.6 microg/l). In the anterior chamber, the triamcinolone concentrations were highest at 3 days after the injection (28.9+/-24.5 microg/l), and in the vitreous, the concentrations were highest at the first day (14,434.0+/-10,768 microg/l). Triamcinolone levels in the vitreous and in the anterior chamber followed a 2-compartment model, with an exponential decrease in the concentration within the first 4 weeks, followed by a steady decline over the following months. At 8 months, the triamcinolone concentrations were 70.7+/-37.0 microg/l in the vitreous samples and 3.3+/-1.6 microg/l in the anterior chamber samples.
Conclusions: The decrease in the concentration of triamcinolone after an intravitreal injection of 6 mg in rabbits follows a 2-compartment model, with an exponential decrease in the first 4 weeks followed by a more linear decrease. During the entire study period, the triamcinolone concentration was significantly higher in the vitreous than in the anterior chamber. After a single intravitreal triamcinolone injection of 6 mg in rabbits, triamcinolone is detectable for at least 8 months after the injection.