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Jorge A. Fortun, Alex Gonzalez, Cornelis Rowaan, Mariela Aguilar, William Lee, Andrew A. Moshfeghi, Thomas A. Albini, Jean-Marie A. Parel; Differential Flow Rate of Triamcinolone and Preservative-Free Triamcinolone through Small-Gauge Needles. Invest. Ophthalmol. Vis. Sci. 2012;53(14):490.
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The most commonly used commercially available steroid preparations used for intravitreal injections are triamcinolone acetonide (TA) (Kenalog 40, Bristol-Myers Squibb, Princeton, NJ) and the preservative-free triamcinolone acetonide (PFTA) (TRIESENCE, Alcon, Inc., Fort Worth, TX) both in the 40-mg/mL formulation. The most commonly used needle for the injection of TA is a 27-gauge needle. Smaller gauge needles are avoided because of the possibility of clogging, presumably caused by obstructive accumulation of triamcinolone aggregates in these narrow needles. PFTA has been shown to form more aggregates of smaller size than TA. We evaluated the differential flow of TA and PFTA through small gauge needles.
A hydraulic piston mechanism was utilized to transfer a constant vertical 1kg gravitational force to the horizontally positioned 1cc syringe plunger (see figure). The 1 kg force was measured during experimental intravitreal injections given by three clinicians (JAF, AAM, TAA). A piezo electric pressure transducer was placed between the syringe and needle. Specialized software developed with Labview, National Instrument platform, was used to digitize and record the pressure signal over time during an injection of 1cc of TA or PFTA through a 27, 30 or 32 gauge needle. All needles were commercially available and 0.5 inches in length. Measurements were performed in triplicate. From each set of measurements we deduced the injection rate (ml/sec). Injections during which flow stopped prior to complete injection of 1cc, were recorded as having a flow rate of 0.
Using a 27-gague needle the mean flow rate of TA was found to be 0.513 cc/sec (±0.064 95% Confidence interval [CI]) and of PFTA 0.620 cc/sec (±0.055 95% CI). Using a 30-gague needle the mean flow rate of TA was found to be 0.06 cc/sec (±0.1 95% CI) and of PFTA 0.180 cc/sec (±0.017 95% CI). Using a 32-gague needle no flow was sustained by TA on any of three attempts and the mean flow rate of PFTA was 0.117 cc/sec (±0.020 95% CI).
PFTA can be injected through a 32 gauge needle but TA cannot. The flow rate of PFTA through a 32-gague is adequate for intravitreal injection, i.e. about 0.1 cc/ sec. This is consistent with the finding of smaller trimacinolone aggregates in PFTA than TA.
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