The Influence of Dead Spaces and the Designs of Injectors on the Amount of Drug Dose in Intra-Vitreal Injection

Abstract

Aim: To evaluate the dead spaces resulting from different designs of the insulin injectors used for intravitreal injections and the amounts of drug doses. Methods: In the study, five different brands of sterile insulin injectors of 1 mL were used for the test. The weight of the injectors was determined before and after filling the injectors with 0.05 and 0.1 mL distilled water. The weight of the injectors was measured with and without the needle after the water within the injectors had been taken out and weight differences were measured. The difference between the intended amount of fluid to be thrown out and the weight of the fluid remaining in the injector was calculated as percent error. Results: After throwing out 0.05 mL distilled water from the injector, weights of the Beybi(R), Traf(R), Becton Dickinson(R), Ayset(R), and Setojet(R) brands of injectors with 30 G needle were detected to increase the mean 0.0220 +/- 0.006 g, 0.0208 +/- 0.008 g, 0.0355 +/- 0.016 g, 0.0219 +/- 0.017 g, and 0.0150 +/- 0.007 g, respectively compared to the weights of the dry injectors. The 0.1 mL injector group was found to be mean 0.0350 +/- 0.014 g, 0.0264 +/- 0.008 g, 0.0405 +/- 0.015 g, 0.0272 +/- 0.013 g, and 0.0245 +/- 0.014 g, respectively. The maximum increase due to the dead spaces in the injectors was found in the Becton Dickinson(R) injector, both in the 0.05 mL and the 0.1 mL groups (p < 0.000). Conclusion: The injector designs may affect the dose of IVI required to be given. More correct amounts of drugs may be administered via the intra-vitreal route through designs that reduce the dead spaces at the end part of the injector and between the inner wall and the plunger.