THE RELATIONSHIP BETWEEN STOPPER POSITION AND INJECTION VOLUME IN RANIBIZUMAB AND AFLIBERCEPT PREFILLED SYRINGES.

Purpose: To determine the relationship between stopper position and injection volume in aflibercept and ranibizumab prefilled syringes (PFS).

Methods: Empty aflibercept 2.0 mg PFS and ranibizumab 0.3 mg and 0.5 mg PFS were collected and refilled with saline. The stopper was positioned relative to the preprinted mark, and resulting injection volumes were recorded. The position for double the on-label volume was confirmed with repeated testing. The quantitative relationship between position and volume was calculated.

Results: In ranibizumab PFS, doubling the distance increased the volume injected by 2.6 times. Positioning the stopper 4.0, 3.0, 2.0, and 0 mm proximal to and 1.0 mm distal to the mark injected volumes of 0.13, 0.1, 0.08, 0.05, and 0.03 mL, respectively. The relationship between position (x) and volume (y) was y = 0.019x + 0.048. In aflibercept PFS, doubling the distance increased the volume injected by 3.2 times. Positioning the stopper 2.5, 2.0, 1.0, and 0 mm proximal to and 1.0 mm distal to the mark injected volumes of 0.16, 0.14, 0.11, 0.05, and 0.02 mL, respectively. The relationship between position (x) and volume (y) was y = 0.041x + 0.059.

Conclusion: Proper positioning of the stopper at the preprinted mark accurately delivers the on-label volume with both the ranibizumab and aflibercept PFS. However, small variations in stopper position appear to have substantial effects on the volume of drug injected.