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Dosage of compounded triamcinolone injections can vary
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MONTREAL - The dosage of intravitreal triamcinolone delivered to the eye by intravitreal injection can vary from case to case within one compounded batch, according to a speaker here at the American Society of Retina Specialists conference.
Gaetano R. Barile, MD, advised physicians to keep this variability in mind “as we evaluate reports of efficacy and side effects” of intravitreal triamcinolone injection.
In an experiment to evaluate the consistency of a typical 4 mg dose of triamcinolone, Dr. Barile withdrew the drug using either a 30-gauge needle or a 27-gauge needle, then prepared a solution of 40 mg/mL, and he evaluated the concentration of the aliquots prepared from that solution after either 10 or 30 shakes. He looked at the effect of each of those parameters on the actual concentration delivered.
“As far as I can tell, it’s pretty difficult to predictably deliver exactly 4 mg of triamcinolone from a 40 mg/mL vial,” he said.
There was essentially no difference between delivery from the 27-gauge needle and the 30-gauge needle, he said.
“What does matter the most is what aliquot you put inside the eye,” he told attendees. “The mean aliquots had a significant blind range, from 1.9 mg to 12.9 mg. The largest doses were concentrated in the last aliquot, so that if you remove the last aliquot from the analysis, dosages decrease and the range tightens up, as does the standard deviation. Removing the last two aliquots lowers the range as well. This tends to reduce the dosage to less than 3 mg.”
In other words, he said, the final two aliquots averaged nearly 8 mg in 0.1 cc, and the final aliquot averaged more than 10 mg in 0.1 cc.
There was no difference or advantage to shaking the bottle 30 times or 10 times, “so 10 times seems to be sufficient for suspending the crystals within the solution,” he said.
Dr. Barile said that, with this method of preparation, surgeons “can’t effectively concentrate the dose, and when you filter it, you certainly do see a decrease in the expected dose.”