Influence of hypodermic needle dimensions on subcutaneous injection delivery - a pig study of injection deposition evaluated by CT scanning, histology, and backflow

Background Thinner and shorter needles for subcutaneous administration are continuously developed. Previous studies have shown that a thinner needle causes fewer occurrences of painful needle insertions and that a shorter needle decreases the occurrence of painful intramuscular injections. However, little is known about local drug delivery in relation to needle length and thickness. This study aimed to compare deposition depth and backflow from three hypodermic needles of 3 similar to mm 34G (0.19 similar to mm), 5 similar to mm 32G (0.23 similar to mm), and 8 similar to mm 30G (0.30 similar to mm) in length and thickness. Methods Ex vivo experiments were carried out on pigs, in neck tissue comparable to human skin at typical injection sites. Six pigs were included and a total of 72 randomized injections were given, i.e. 24 subcutaneous injections given with each needle type. Accordingly, 400 similar to mu L was injected including 70% NovoRapid (R) (Novo Nordisk A/S, Bagsv mu rd, Denmark) and 30% Xenetix (R) (Guerbet, Villepinte, France) contrast including 1 similar to mg/mL Alcian blue. Surgical biopsies of injection sites were sampled and computer topographic (CT)-scanned in 3D to assess deposition and local distribution. Biopsies were prepared and stained to evaluate deposition in comparison to the CT-scanning findings. The backflow of each injection was collected with filter paper. The blue stains of filter paper were digitized and volume estimated by software calculation vs. control staining. Results CT-scanning (n similar to=similar to 57) and histology (n similar to=similar to 10) showed that, regardless of injection depth, the bulk of the injection was in the subcutaneous tissue and did not propagate from subcutis into dermis. With the 8 similar to mm 30G needle all injections apart from one intramuscular injection were located in the subcutaneous layer. The volume depositions peaked in 45 similar to mm depth for the 3 similar to mm 34G needle, in 56 similar to mm depth for the 5 similar to mm 32G needle, and in 910 similar to mm depth for the 8 similar to mm 30G needle. In general, injection depositions evaluated by histology and CT-scans compared well for the individual biopsies. The amount of backflow (n similar to=similar to 69) from the 3 similar to mm 34G needle was smaller (P similar to