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M.D. Ober, S. Tari, G. Tosi, G. Barile; Measurement of Actual Triamcinolone Acetonide Dose . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4732.
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Purpose: To measure the dose of triamcinolone acetonide (TA) delivered during an intravitreal injection using multiple techniques. Methods: A 1ml vial of TA (Kenalog–40, Bristol–Myers–Squibb) was prepared according to 1 of 4 protocols. In group 1, TA was drawn into a 1ml syringe after shaking the vial 10 or 30 times. A 0.1 ml aliquot of TA suspension was then dispensed with a 30 gauge needle and weighed after drying. Group 2 employed a 27 gauge needle to allot 0.1ml. Group 3 concentrated TA by allowing a 1ml vial to settle for 24 hours upside–down. After removing the clear supernatant, the crystals were then withdrawn into a 1ml syringe and the mass determined after drying. Group 4 produced concentrated TA by washing the TA crystals with a saline solution. The contents of a TA vial were drawn into a 1ml syringe and capped with a 0.2 µm micropore filter. This was placed on a 3–way stopcock along with a normal saline filled syringe. The TA suspension was then pushed through the filter. 1cc saline then forced the crystals back into the syringe via the stopcock and filter. The new suspension was again pressed through the filter and the process was repeated a total of 3 times. Finally, 0.2cc saline was forced through the stopcock and filter yielding the mixture which was dispensed with a 30g needle, dried, and weighed. 2–tailed student t–tests were used in statistical analysis. Results: The initial 70% of TA delivered from a 1ml syringe differed significantly from the final 30% (p<0.0001). A mean (± SD) of 3.79 ± 1.47mg was delivered from the first 70%, while the final 30% produced an average of 13.15 ± 4.8mg from groups 1 and 2. TA dispensed from a 30 gauge needle in group 1 yielded a mean of 3.38 ± 1.85mg and was not significantly different from the 27 gauge needle used in Group 2 (p=.99) where a mean of 3.23 ± 1.66mg was found. There was no statistical difference between shaking the TA vial 30x or 10x prior to use (p=.86) combining Groups 1 and 2. The concentrated TA suspension produced in Group 3 generated an average of 32.08 ± 7.04mg. After washing the TA crystals free from vehicle according to the method described for Group 4, an average of 25.23 ± 1.66mg TA was generated.Conclusions:Regardless of method of preparation, efforts to achieve a 4.0mg injection of TA are variable and inconsistent suggesting that a range of dosages are delivered intravitreally using current techniques. Care must be taken not to inject TA from the final 30% of that drawn from a 1 ml vial into a syringe likely due to a relative filtering of crystals when forcing the suspension through a small gauge needle. Clinical investigations of intravitreal TA should take into account the variability of dose delivered when assessing drug efficacy and side–effects.
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