A 2007 article by a single author discusses the risk of coring when retrieving medicine from a vial, along with suggestions on how to draw up medication. It is noted that the quality of manufacturing can affect the risk of coring. Drugs developed in developing countries may result in medication packaging with an increased risk of coring due to lower quality control measures. A longstanding technique for reducing risk of coring is to insert the needle at a 45-60° angle with the opening of the needle tip facing up and away from the stopper. Then, a small amount of pressure is applied and the angle is gradually increased as the needle enters the vial. The needle should be at 90° angle just as the needle bevel passes through the stopper. While smaller gauges might decrease risk of coring, it would also make the particulate smaller should it still occur. [1]

A 2021 study evaluated the incidence of coring when using different angled penetration techniques with single-use hypodermic needles. This study tested the hypothesis that fully penetrating with the needle at 45-60° followed by gradual rotation of the needle until perpendicular to the stopper surface will minimize coring by replicating the technique using 18G, 20G, 22G, and 30G needles. Three alterations to the techniques were tested: bevel up, bevel down, or bevel to the side. Additional to the bevel orientation, each needle was also tested based on angle pressure: pressure along the 45° angle or downward pressure (perpendicular to the stopper surface). After each method, the contents were filtered through a 20 mcm filter paper and examined with a magnifying glass and via microscope. Results found three notable findings: for needles larger than 22G, the bevel-down position performs the worst; the bevel-up position performs most reliably for all needle sizes and bevel orientations; and the dominating factor for downward pressure penetration appears to be the bevel position. Overall, these results suggest using a bevel-up 45° penetration is the most optimal to prevent coring. [2]

A 2022 experimental study investigated the impact of different variables on rubber core contamination when puncturing rubber stoppers of multi-dose propofol vials. Various needle sizes (18G, 20G, 21G) and 45° and 90° angles of piercing were compared. Propofol vials (50 mL) were emptied and then filled with 25 mL of sterile water. Rubber stoppers were punctured with an upward bezel and compression force of 10 N, 3 times at different sites for one set, 25 sets for each of 6 settings: 18G at 45°; 18G at 90°; 20G at 45°; 20G at 90°; 21G at 45°; and 21G at 90°. After the 3rd puncture, 1 mL of sterile water was flushed through the needle. Particulate matter in vials was evaluated under a stereomicroscope at 100x magnification. No difference was found in the size of the coring that occurred while using different gauge needles at either angle. However, a significantly higher incidence of rubber coring was observed with the 18G needle punctured at 45° vs. 90° (56% vs. 20%; p= 0.01). Overall, an 18G needle was associated with a significantly higher number of particulate matter compared to 20G and 21G (28% vs. 8% vs. 6%; p<0.01). Use of a large-bore needle was concluded to be the most notable factor for rubber coring, regardless of puncture angle, but especially when the 18G needle was inserted at 45°. [3]

Basic vector principles dictate the amount of force required to pierce a rubber stopper in the vertical plane is reduced with an angled approach (i.e., 45°) compared with a perpendicular approach (i.e., 90°). While this has been shown to be true with sharp beveled needles, a 2015 study compared the angled versus perpendicular approach to reduce coring with plastic blunt fill needles. Rubber stoppers of propofol 1% 20 mL vials (Diprivan®; AstraZeneca) were punctured with BD short plastic blunt fill needles approximately 500 times, 250 times with each technique. Coring occurred in 29.2% of the perpendicular punctures compared with 15.2% when an angled approach was used (p= 0.0001). As such, using an angled approach with plastic blunt needles can reduce the incidence of coring by approximately 50%. Notably, only a visual inspection was conducted to assess coring and there was no discussion on if techniques were alternated or done consecutively. [4]

A 2021 study investigated the frequency of vial coring among 800 vials of 2 mL sodium chloride products. The vials were divided into four groups (n= 22). Groups 1 and 2 aspirated the vial with an 18G needle and ejected the fluid using an 18G and 23G needle, respectively. Group 3 used a 23G needle for both aspiration and ejection. Group 4 used an 18G needle with 5 mcm filters. The needle was inserted exactly in the center at a 90° angle. Comparisons between other angles of puncture were not performed. None of the 800 specimens observed particulates. However, microscopic investigations found that 20 (10%) rubber particles were detected in Group 1, 21 (11%) in group two and 65 (33%) in Group 3. In Group 4, no particles were visualized. Based on these results, the authors recommend ways to circumvent piercing a rubber stopper altogether (i.e., remove stopper, use prefilled syringe, use filter needle). The authors note that needle insertion at a 45-60° angle may not always be possible in daily practice such as orthopedic procedures where a nurse and surgeon must balance the vial for aspiration at 90°. [5]

A 2014 study investigated the difference in coring frequency when using a blunt versus sharp needle to pierce rubber-topped vials. An 18G sharp hypodermic needle or blunt plastic (safety) needle were used. The angle of administration was not specified. The incidence of coring occurred in 102 of 250 (40.8%) vials with a blunt needle vs 9 of 215 (4.2%) vials with a sharp needle (p<0.0001). These findings suggest that use of blunt needles poses a potential patient safety hazard. [6]