When administering insulin via subcutaneous injections, consistency of the injection and dose accuracy are essential; the user must receive the dialed and expected dose of insulin. One commonly known and well discussed event, which may occur after an injection, is the leakage of fluid out of the skin at the injection site, commonly referred to as either leakage or backflow.Studies indicate that the amount of detected leakage is not of clinical significance.1-4 However, leakage influences the patient perception of insulin administration, because the patients are concerned whether they have received the correct dosage.5-7 Therefore, clinicians may be consulted by concerned patients to support their choice of injection technique and pen needle.The present article investigates how different injection techniques and needle design factors potentially influence the volume and frequency of leakage following subcutaneous injections. Identified from a literature study of leakage, these factors were chosen to be injection region (abdomen or thighs), injection volume, injection speed, needle wall thickness, needle taper (outer shape of needle), needle insertion angle into the skin, and wait time after an injection until the needle is withdrawn from the skin. The 3 first mentioned factors were informed by analyzing unpublished leakage data from a previous clinical trial, 8 and the 4 latter factors were investigated in an exploratory leakage study on pigs. See Table 1 for an overview of the identified factors potentially influencing leakage, and our choice of data to substantiate our recommendation pertaining to these factors. Method: Leakage data were obtained from a post hoc analysis of clinical trial data and from a pig study. Data from the clinical study were used to determine leakage as a function of injection volume, speed and region. Data from the pig study were used to determine leakage as a function of needle wall thickness, needle taper, injection angle, and wait time from end of injection to withdrawal of needle from skin.Results: Leakage volume was positively related to injection volume. Injections in the abdomen caused less leakage than thigh injections. A 32G needle caused less leakage than a 31G and a 32G tip (tapered) needle, and a "straight in" 90° needle insertion angle caused less leakage than an angled (~45°) insertion. Wait times of minimum 3 seconds caused less leakage than immediate withdrawal of the needle after injection. Needle wall thickness and injection speed did not influence leakage.Conclusions: Leakage will be minimized using a thin needle, using 90° needle insertion in the abdomen, injecting maximum 800 µL at a time, and waiting at least 3 seconds after the injection until the needle is withdrawn from the skin.

ObjectivePen needles used for subcutaneous injections have gradually become shorter, thinner and more thin walled, and thereby less robust to patient reuse. Thus, different needle sizes, alternative tip designs and needles resembling reuse were tested to explore how needle design influences ease of insertion, pain and skin trauma.Research design and methods30 subjects with injection-treated type 2 diabetes and body mass index 25–35 kg/m2 were included in the single-blinded study. Each subject received abdominal insertions with 18 different types of needles. All needles were tested twice per subject and in random order. Penetration force (PF) through the skin, pain perception on 100 mm visual analog scale, and change in skin blood perfusion (SBP) were quantified after the insertions.ResultsNeedle diameter was positively related to PF and SBP (p<0.05) and with a positive pain trend relation. Lack of needle lubrication and small ‘needle hooks’ increased PF and SBP (p<0.05) but did not affect pain. Short-tip, obtuse needle grinds affected PF and SBP, but pain was only significantly affected in extreme cases. PF in skin and in polyurethane rubber were linearly related, and pain outcome was dependent of SBP increase.ConclusionsThe shape and design of a needle and the needle tip affect ease of insertion, pain and skin trauma. Relations are seen across different data acquisition methods and across species, enabling needle performance testing outside of clinical trials.Trial registration numberNCT02531776; results.

Approximately 382 million people worldwide have diabetes, 1 half of the prevalent cases are not known or diagnosed, half of those diagnosed are not treated, and half of those treated are not controlled. 2,3 One of the reasons for poor treatment compliance is injection anxiety causing 20% of insulin users to sometimes skip their injections, and 10% to restrict their number of injections. 4 As many as 94% of insulin users exhibit symptoms of anxiety, distress, or phobia around blood and injury from injections, 5 22% of insulin users have to mentally prepare themselves for injections, 6 and 33% of insulin users dread their injections. 7 This underlines why it is of high importance to develop needle designs that cause as little fear, injury, and pain as possible. Pain perception is one of the preferred methods to evaluate new needle design. 8-18 Studies have shown how needle diameter correlates with both the magnitude of the perceived pain, typically measured on visual analog scales (VASs), and with pain occurrence, that is, how often the needle causes pain sensation. 11-13 However, pain is a subjective measure with a large number of biasing variables causing data with high variance. Therefore, a high sample size is needed to detect differences in pain, which makes it both costly and time-consuming to carry out the clinical trials. One alternative way to obtain information about the needle impact on tissue is to use animal models, where histology can be used to assess tissue trauma from, for example, a needle insertion. The needle insertion can cause tissue bleeding and initiate inflammation in the tissue. Pig models are especially useful when examining skin disease and wound 531099D STXXX10.

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