Assessment of Forces in Intradermal Injection Devices: Hydrodynamic Versus Human Factors.

PURPOSE: The force that has to be exerted on the plunger for administering a given amount of fluid in a given time, has an important influence on comfort for the subject and usability for the administrator in intradermal drug delivery. The purpose of this study is to model those forces that are subject-independent, by linking needle and syringe geometry to the force required for ejecting a given fluid at a given ejection rate. MATERIAL AND METHODS: We extend the well-known Hagen-Poiseuille formula to predict pressure drop induced by a fluid passing through a cylindrical body. The model investigates the relation between the pressure drop in needles and the theoretic Hagen-Poiseuille prediction and is validated in fifteen needles from 26G up to 33G suited for intradermal drug delivery. We also provide a method to assess forces exerted by operators in real world conditions. RESULTS: The model is highly linear in each individual needle with R-square values ranging from 75% up to 99.9%. Ten out of fifteen needles exhibit R-square values above 99%. A proof-of-concept for force assessment is provided by logging forces in operators in real life conditions. CONCLUSIONS: The force assessment method and the model can be used to pinpoint needle geometry for intradermal injection devices, tuning comfort for subjects and usability for operators.

Assessment of acceptability and usability of new delivery prototype device for intradermal vaccination in healthy subjects.

The objectives of this study were to assess the acceptability and usability of a newly developed intradermal prototype device, VAX-ID™, in healthy subjects. In April 2012 an investigational study was conducted in healthy subjects aged 18 to 65 y. To compare injection site and route of administration, subjects were allocated to 4 subgroups, either receiving subsequently 2 intradermal (ID) injections (one in the forearm and one in the deltoid) or an ID (forearm) and an intramuscular (IM) (deltoid) injection. All injections contained saline solution. Acceptability was assessed with a subjects' questionnaire and a daily electronic diary for 5 d. Usability was assessed with a vaccinators' questionnaire and an expert panel. A 10-point Visual Analog Scale was used to score several statements on usability and acceptability. A total of 102 healthy subjects were enrolled in the study (age: 19-63). No statistically significant differences were seen in demographic characteristics between the ID and IM groups. Anxiety before injection, pain during injection and duration of injection were rated significantly lower for ID compared to IM. One day after the injections, redness was reported more often after ID injection in the forearm versus ID in the deltoid; pain at injection site was reported significantly more often after IM vs. ID injection. The new VAX-ID prototype device was found easy to handle, easy to use and safe. The new VAX-ID prototype device was shown to have a high degree of acceptability as well as usability. Further studies with VAX-ID will be conducted using vaccine antigen allowing assessment of immunogenicity and safety. Additionally, these studies will help to further improve VAX-ID in terms of accuracy of delivered dose and feedback to the vaccinator. (NCT01963338).