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C.A. Lemley, D.A. Saperstein; Injection Quantity Decreases With Delivery Delay in an in vitro Model of Intravitreal Triamcinolone Acetonide Injection . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1456.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the effect of needle gauge size and injection delay after sample preparation on triamcinolone acetonide intravitreal injection. Design: In–vitro experimental model. Methods: Multiple 0.1 cc samples of triamcinolone acetonide (Kenolog–40, 40 mg/ml; Bristol–Myer Squibb, Princeton, NJ) were prepared by standard methods for intravitreal injection in 1cc tuberculin syringes. Samples were injected into test tubes through 27 and 30 gauge needles both immediately after preparation and after 5 minutes of sitting horizontally on a bench top. Total injection quantities were determined by spectrophotometer at 240nm wavelength using absorbance concentration curve with standard methodology. The difference between groups was determined with the unpaired student–t test. Results: Final triamcinolone acetonide mean doses were 4.7 mg (range 4.2–4.9 mg) and 4.3 mg (range 3.9–4.7mg) through 27 and 30 gauge needles respectively when injected immediately after sample preparation. Mean dose quantities dropped to 2.8 mg (range 2.3–3.5) and 2.5 mg (range 1.8–3.2 mg) with 27 and 30 gauge needles when sample injections were delayed for 5 minutes. This differences were significant with both 27 gauge (p<0.0001) and 30 gauge needles (p<0.0001) respectively. This represents drug dose loss of 40% and 43% after 5 minutes of delay with 27 and 30 gauge needles. There was no statistically significant difference between the 30 gauge needles and the 27 gauge needles at either the immediate time point or at 5 minutes, p = 0.0544 and p = 0.1917, respectively. Conclusions: Previous studies have shown variation of intraocular triamcinolone acetonide concentrations after intravitreal injection. In this study, we hypothesize that inadvertent variation in injection quantities may be involved. With an in–vitro model, we demonstrate approximate 40% decrease in injection drug quantities after 5 minutes of delay compared to immediate injection with both 27 and 30 gauge needles. This is likely due to sedimentation of the drug during delay and filtering effect of the needle hub. We did not see a difference between 27 gauge and 30 gauge needles. This study reinforces the importance of prompt injection of triamcinolone acetonide after sample preparation.
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