Purpose: To describe the pharmacokinetics occurring after the direct injection of triamcinolone acetonide into the vitreous humor of humans. Design: Interventional case series. Participants: Five patients who received a single 4-mg intravitreal injection of triamcinolone acetonide. Methods: An aqueous humor sample was obtained from 5 eyes via an anterior chamber paracentesis at days 1, 3, 10, 17, and 31 after injection. At each visit, visual acuity and intraocular pressure were measured and indirect ophthalmoscopy was performed. A fluorescein angiogram was carried out at day 10. Concentrations were determined using high performance liquid chromatography; pharmacokinetic analysis was carried out using PK Analyst, an iterative, nonlinear, weighted, least-squares regression program. Main Outcome Measures: Intraocular concentrations of triamcinolone were measured and population pharmacokinetic parameters were calculated. Results: Pharmacokinetic data followed a two-compartment model. Peak aqueous humor concentrations ranged from 2151 to 7202 ng/ml, half-lives from 76 to 635 hours, and the integral of the area under the concentration-time curve (AUC-t) from 231 to 1911 ng/h per milliliter. After a single intravitreal injection of triamcinolone, the mean elimination half-life was 18.6 days in nonvitrectomized patients. The half-life in a patient who had undergone a vitrectomy was shorter at 3.2 days. Conclusions: There was considerable intrasubject variation among peak concentration, AUC-t values, and elimination half-lives. After intravitreal injection, measurable concentrations of triamcinolone would be expected to last for approximately 3 months (93 ± 28 days) in the absence of a vitrectomy. Because triamcinolone pharmacokinetics were characterized only in elderly patients with macular edema, the results cannot be extrapolated to other patient populations.
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