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K.G. Csaky, H. Coleman, S. Dahr, E. Chew, J. Rosenthal, W. Gilmer, H. Kim, P. Yuan, S. Cousins, M. Robinson; Anterior Subtenon's Triamcinolone Acetonide (ASTTA) Injection for the Treatment of Diabetic Macular Edema: Animal and Clinical Findings . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4670.
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Purpose: While intraocular injection of steroid is under study for the treatment of diabetic macular edema (DME), extraocular routes are also being investigated. Previously, we have demonstrated that transcleral drug delivery through the posterior sclera may enter the eye through a portal of entrance just posterior to the ciliary body (IOVS 45: 2722 (2004). Therefore, the present study was undertaken to see if triamcinolone acetonide (TA) delivered to the anterior subtenon’s space (AST) enters into the eye and demonstrates clinical effects on DME. Methods: 20 mg of TA in the form of a small particle (median size = 5 µm) preservative–free suspension (TAC–PF) or 40 mg of a large particle (mean size = 17.3 µm) preservative containing formulation (Kenalog®) was injected into the AST of NZW rabbits and vitreous levels of TA were measured by HPLC at days 1, 3 and 7 (n= 27). 15 eyes of 13 patients with clinically significant DME as detected by fluorescein angiography and optical coherence tomography (OCT) were injected with 20 mg of Kenalog® into the AST and followed over 4 to 9 weeks. Central OCT thickness was determined by manual measurement of absolute thickening (actual measurement in µm minus 175 µm). Results: ASTA both in small particle and large particle formulation entered the vitreous in rabbits through the sclera but demonstrated different pharmacokinetic profiles. TAC–PF showed peaked levels of 12.25 µM +/– 6.1 µM* at 1 day while peak levels of Kenalog® were 3.5 µM +/– 0.69 µM* at day 3. Both formulations resulted in detectable vitreous levels at day 7 at comparable levels (2.6 µM). Overall the total amount of drug found in the vitreous over the 7 days was higher with TAC–PF (11 µg) than with Kenalog® (3.1 µg). Clinically, 9/15 eyes showed an improvement in DME as measured by OCT, with an absolute retinal thickening decrease over the treatment period of 113 µm +/– 33 µm*, 4/15 showed no change and 2/15 worsened. Mean visual acuities and intraocular pressures remained unchanged. An increased in the amount of conjunctival hyperemia over the injection site occurred in some patients. Conclusions: Injection of TA into the AST results in transcleral penetration of drug. Penetrance appears to be dependent on TA particle size. Early clinical experience with ASTTA suggests a therapeutic effect on DME with an absence of short–term complications. However, longer term and more complete clinical trials are needed to assess the efficacy and safety of ASTA for DME. (* mean +/– SEM).
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