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

Backflow reduction in local injection therapy with gelatin formulations

The local injection of therapeutic drugs, including cells, oncolytic viruses and nucleic acids, into different organs is an administrative route used to achieve high drug exposure at the site of action. However, after local injection, material backflow and side effect reactions can occur. Hence, this study was carried out to investigate the effect of gelatin on backflow reduction in local injection. Gelatin particles (GPs) and hydrolyzed gelatin (HG) were injected into tissue models, including versatile training tissue (VTT), versatile training tissue tumor-in type (VTT-T), and broiler chicken muscles (BCM), using needle gauges between 23 G and 33 G. The backflow material fluid was collected with filter paper, and the backflow fluid rate was determined. The backflow rate was significantly reduced with 35 μm GPs (p value < .0001) at different concentrations up to 5% and with 75 μm GPs (p value < .01) up to 2% in the tissue models. The reduction in backflow with HG of different molecular weights showed that lower-molecular-weight HG required a higher-concentration dose (5% to 30%) and that higher-molecular-weight HG required a lower-concentration dose (7% to 8%). The backflow rate was significantly reduced with the gelatin-based formulation, in regard to the injection volumes, which varied from 10 μL to 100 μL with VTT or VTT-T and from 10 μL to 200 μL with BCM. The 35 μm GPs were injectable with needles of small gauges, which included 33 G, and the 75 μm GPs and HG were injectable with 27 G needles. The backflow rate was dependent on an optimal viscosity of the gelatin solutions. An optimal concentration of GPs or HG can prevent material backflow in local injection, and further studies with active drugs are necessary to investigate the applicability in tumor and organ injections.

Rose Bengal Labeled Bovine Serum Albumin for Protein Transport Imaging in Subcutaneous Tissues Using Computed Tomography and Fluorescence Microscopy

Subcutaneous (SC) injection of protein-based therapeutics is a convenient and clinically established drug delivery method. However, progress is needed to increase the bioavailability. Transport of low molecular weight (Mw) biotherapeutics such as insulin and small molecule contrast agents such as lipiodol has been studied using X-ray computed tomography (CT). This analysis, however, does not translate to the investigation of higher Mw therapeutics, such as monoclonal antibodies (mAbs), due to differences in molecular and formulation properties. In this study, an iodinated fluorescein analog rose bengal (RB) was used as a radiopaque and fluorescent label to track the distribution of bovine serum albumin (BSA) compared against unconjugated RB and sodium iodide (NaI) via CT and confocal microscopy following injection into ex vivo porcine SC tissue. Importantly, the high concentration BSA-RB exhibited viscosities more like that of viscous biologics than the small molecule contrast agents, suggesting that the labeled protein may serve as a more suitable formulation for the investigation of injection plumes. Three-dimensional (3D) renderings of the injection plumes showed that the BSA-RB distribution was markedly different from unconjugated RB and NaI, indicating the need for direct visualization of large protein therapeutics using conjugated tags rather than using small molecule tracers. Whereas this proof-of-concept study shows the novel use of RB as a label for tracking BSA distribution, our experimental approach may be applied to high Mw biologics, including mAbs. These studies could provide crucial information about diffusion in SC tissue and the influence of injection parameters on distribution, transport, and downstream bioavailability.

Modeling drug transport and absorption in subcutaneous injection of monoclonal antibodies: Impact of tissue deformation, devices, and physiology

The pharmaceutical industry has experienced a remarkable increase in the use of subcutaneous injection of monoclonal antibodies (mAbs), attributed mainly to its advantages in reducing healthcare-related costs and enhancing patient compliance. Despite this growth, there is a limited understanding of how tissue mechanics, physiological parameters, and different injection devices and techniques influence the transport and absorption of the drug. In this work, we propose a high-fidelity computational model to study drug transport and absorption during and after subcutaneous injection of mAbs. Our numerical model includes large-deformation mechanics, fluid flow, drug transport, and blood and lymphatic uptake. Through this computational framework, we analyze the tissue material responses, plume dynamics, and drug absorption. We analyze different devices, injection techniques, and physiological parameters such as BMI, flow rate, and injection depth. Finally, we compare our numerical results against the experimental data from the literature.

The Needle Shield Size and Applied Force of Subcutaneous Autoinjectors Significantly Influence the Injection Depth

BACKGROUND

This study examines how shield-triggered autoinjectors (AIs), for subcutaneous drug delivery, affect injection depth. It focuses on shield size and applied force, parameters that could potentially lead to inadvertent intramuscular (IM) injections due to tissue compression.

METHOD

A blinded ex-vivo study was performed to assess the impact of shield size and applied force on injection depth. Shields of 15, 20, and 30 mm diameters and forces from 2 to 10 N were investigated. The study involved 55 injections in three Landrace, Yorkshire, and Duroc (LYD) pigs, with injection depths measured with computed tomography (CT). An in-vivo study, involving 20 injections in three LYD pigs, controlled the findings, using fluoroscopy (FS) videos for depth measurement.

RESULTS

The CT study revealed that smaller shield sizes significantly increased injection depth. With a 15 mm diameter shield, 10 N applied force, and 5 mm needle protrusion, the injection depth exceeded the needle length by over 3 mm. Injection depth increased with higher applied forces until a plateau was reached around 8 N. Both applied force and size were significant factors for injection depth (analysis of variance [ANOVA], P < .05) in the CT study. The FS study confirmed the ex-vivo findings in an in-vivo setting.

CONCLUSIONS

The study demonstrates that shield size has a greater impact on injection depth than the applied force. While conducted in porcine tissue, the study provides useful insights into the relative effects of shield size and applied force. Further investigations in humans are needed to confirm the predicted injection depths for AIs.

Characterization of pig skin microbiome and appraisal as an in vivo subcutaneous injection model

Pig skin is commonly used in the medical industry as an injection model due to its compelling physiological affinity to human skin. However, the pig neck skin microflora remains largely uncharacterized, which may have undesirable implications for the translatability of results to humans. This study aimed to characterize pig neck skin microbiome with direct comparison with human skin microflora at emblematic injection sites to appraise its suitability as an injection model. Ten minipigs were sampled with tape strips and swabs and analysed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and 16S/ITS high throughput sequencing and confocal laser scanning microscopy. Results were directly compared with previous investigations of human injection sites. Pig skin was dominated by phyla 94.8% Firmicutes, 3% Proteobacteria, and 2.2% Actinobacteria. Staphylococcus spp. prevailed (44.4%) at the genus level with S. capitis and S. chromogenes present in all samples. Pig skin revealed populations in the 104 colony-forming units (CFU)/cm2 range with 3% identified as Gram-negative and increased alpha diversity (compared with 102 CFU/cm2 and 10% in humans). While notable taxonomical differences on species levels were seen, pig skin encompassed 97.1% of genera found in human samples. The increased population and variation found support the pig neck as an imperfect but fidelitous subcutaneous injection model that can adequately challenge devices from a microbial standpoint.

Magnetic Resonance Imaging Used to Define the Optimum Needle Length in Pigs of Different Ages

Intramuscular injections result in tissue destruction and alteration. Therefore, it is necessary to evaluate the optimum injection point for intramuscular injections. As animals—especially pigs—vary in size and explicit information about injection depth is not available. To determine the predicted optimum injection depth, magnetic resonance imaging was used in pigs of different ages and weight groups. In total, 730 magnetic resonance images of 136 pigs were used to calculate the optimum injection depth for intramuscular injections. Four age groups were evaluated: <29 days of age, 29−70 days of age, 71−117 days of age and >170 days of age. For fattening pigs (71−117 days of age), the present study recommends a needle length of 20 mm (range: 40−58 mm). For younger pigs (<70 days of age), a needle length of 12 to 14 mm (range: 10−18 mm), and for older pigs (>170 days of age), a needle length of 30 mm (range: 25−37 mm) is recommended. However, more data are needed. Therefore, further studies are necessary, especially in the youngest (suckling pigs) and oldest (sows) age groups, as these are the groups mainly injected/vaccinated. Additionally, age and weight should be examined in more detail compared to fat distribution in the neck, genetics and the sex of the animal.

Optimizing ethyl cellulose-ethanol delivery towards enabling ablation of cervical dysplasia

In low-income countries, up to 80% of women diagnosed with cervical dysplasia do not return for follow-up care, primarily due to treatment being inaccessible. Here, we describe development of a low-cost, portable treatment suitable for such settings. It is based on injection of ethyl cellulose (EC)-ethanol to ablate the transformation zone around the os, the site most impacted by dysplasia. EC is a polymer that sequesters the ethanol within a prescribed volume when injected into tissue, and this is modulated by the injected volume and delivery parameters (needle gauge, bevel orientation, insertion rate, depth, and infusion rate). Salient injection-based delivery parameters were varied in excised swine cervices. The resulting injection distribution volume was imaged with a wide-field fluorescence imaging device or computed tomography. A 27G needle and insertion rate of 10 mm/s achieved the desired insertion depth in tissue. Orienting the needle bevel towards the outer edge of the cervix and keeping infusion volumes ≤ 500 µL minimized leakage into off-target tissue. These results guided development of a custom hand-held injector, which was used to locate and ablate the upper quadrant of a swine cervix in vivo with no adverse events or changes in host temperature or heart rate. After 24 h, a distinct region of necrosis was detected that covered a majority (> 75%) of the upper quadrant of the cervix, indicating four injections could effectively cover the full cervix. The work here informs follow up large animal in vivo studies, e.g. in swine, to further assess safety and efficacy of EC-ethanol ablation in the cervix.

Probabilistic modeling of an injectable aqueous crystalline suspension using influence networks

Probabilistic modeling using influence networks is an efficient, intuitive, and easy to communicate strategy in the development of complex pharmaceutical products. This study was aimed to use a risk-based approach to explore the complex interactions between product and process design parameters affecting size and shape of the particles in injectable aqueous crystalline suspensions (ACS). Based on a risk assessment, a design of experiments (DOE) was applied to evaluate the most important parameters, i.e., four critical material attributes and two critical process parameters. A model hydrophobic drug (carbamazepine) was milled and homogenized in a multistep process (dispersion and milling steps). The final formulations were characterized with automated at-line image analysis of thousands of individual particles. The particle size and shape distributions were summarized with descriptive parameters, and the relationship of these parameters and the DOE was modeled using influence networks (INs). This approach was compared and contrasted with a classical modeling approach based on multivariate linear regression (MVLR). INs had a superior visual interpretation capability of the complex and multivariate ACS system making the risk-based decision making more accessible. The probability and causality were included in the IN, i.e., the relationships between size and shape. Moreover, IN allowed to incorporate prior knowledge in a systematic way by implementing a 'black and white list'. An IN based model was created with the following model performance: a mean absolute percentage error of 1.7% and 1.1% for the size and 6.2% and 5.0% for the shape, respectively for dispersed and milled ACS. Parameters with the highest and lowest probability to control the critical quality attributes of ACS could be identified. Consequently, the parameter settings giving the optimum particle size and shape could be predicted using a Monte Carlo simulation to calculate the probability of success including the uncertainty of the model. The cubic MVLR model for the size of milled ACS was comparable to the IN in terms of the mean absolute percentage error, i.e., 1.1%. However, IN was more efficient in visualizing the complex and multivariate data set, including all the critical quality attributes and formulation/process parameters of the ACS at the same time. Moreover, the prior knowledge used in probabilistic modeling of IN could be systematically documented.

Understanding Factors Governing Distribution Volume of Ethyl Cellulose-Ethanol to Optimize Ablative Therapy in the Liver

OBJECTIVE

Ethanol ablation, the injection of ethanol to induce necrosis, was originally used to treat hepatocellular carcinoma, with survival rates comparable to surgery. However, efficacy is limited due to leakage into surrounding tissue. To reduce leakage, we previously reported incorporating ethyl cellulose (EC) with ethanol as this mixture forms a gel when injected into tissue. To further develop EC-ethanol injection as an ablative therapy, the present study evaluates the extent to which salient injection parameters govern the injected fluid distribution.

METHODS

Utilizing ex vivo swine liver, injection parameters (infusion rate, EC%, infusion volume) were examined with fluorescein added to each solution. After injection, tissue samples were frozen, sectioned, and imaged.

RESULTS

While leakage was higher for ethanol and 3%EC-ethanol at a rate of 10 mL/hr compared to 1 mL/hr, leakage remained low for 6%EC-ethanol regardless of infusion rate. The impact of infusion volume and pressure were also investigated first in tissue-mimicking surrogates and then in tissue. Results indicated that there is a critical infusion pressure beyond which crack formation occurs leading to fluid leakage. At a rate of 10 mL/hr, a volume of 50 μL remained below the critical pressure.

CONCLUSIONS

Although increasing the infusion rate increases stress on the tissue and the risk of crack formation, injections of 6%EC-ethanol were localized regardless of infusion rate. To further limit leakage, multiple low-volume infusions may be employed.

SIGNIFICANCE

These results, and the experimental framework developed to obtain them, can inform optimizing EC-ethanol to treat a range of medical conditions.

User experience for manual injection of 2 mL viscous solutions is enhanced by a new prefillable syringe with a staked 8 mm ultra-thin wall needle

OBJECTIVES

User experience was compared between a new pre-fillable 2.25 mL glass syringe equipped with an ultra-thin-wall (UTW) 8 mm staked needle and a marketed BD Neopak™ syringe equipped with a special-thin-wall (STW) 12.7 mm staked needle.

METHODS

Participants simulated subcutaneous injections with both syringes alone (formative Human Factors study) and in combination with a needlestick-prevention device (validation Human Factors study).

RESULTS

Usability results of both studies showed higher success rates for delivering the full dose of 2 mL viscous solution (30 cP) with the 8mmUTW syringe than with the 12.7mmSTW one (63% vs. 42% in the formative study). The use of the 8mmUTW syringe demonstrated also better ease of use and acceptance results and 72% of formative study participants preferred this new syringe over the current one when delivering the viscous solution. Using a shorter needle also showed a benefit in decreasing the injection-related anxiety. Besides, in the case of a non-recommended injection technique, the calculated risk of accidental intramuscular injection is reduced by 2 to 13 times with the 8mmUTW syringe.

CONCLUSION

Altogether, the results obtained demonstrated an improvement of the user experience with this new syringe compared to the current one in the manual delivery of 2 mL viscous solutions.

Spread of fluid: Role of tip configurations in needles

BACKGROUND/PURPOSE

During the injection of a fluid in a tissue model, the fluid might be affected by the needle tip configuration and the number of channels. Thus, the objective of the present work is to observe the influence of different needle tips and number of channels on the spread of a fluid.

METHODS

Fluid distribution data were obtained after injecting 0.3 mL of fluid into a foamed polymer model with a velocity of 2 mm/s. The spread area and the depth were determined for 3 different types of hypodermic needles: Single channel needles with bevel tip and blunt tip and a needle with conical tip and 3 internal channels.

RESULTS

The bevel tip provides a higher spread in the direction where the bevel points and reaches larger depths than the other two needles. The spread for the blunt tip and the polymer needle is equally distributed on both sides of the needle. The largest horizontal area around the tip is achieved by the 3-channel needle.

CONCLUSION

The tip configuration and number of channels have an influence on the distribution of fluid. The bevelled needle directs the fluid and reaches larger depths compared with the 3-channel needle that gets more horizontal spread.

Insulin amyloid at injection sites of patients with diabetes

The formation of insulin amyloid can dramatically impact glycemic control in patients with diabetes, making it an important therapeutic consideration. In addition, the cost associated with the excess insulin required by patients with amyloid is estimated to be $3K per patient per year, which adds to the growing financial burden of this disease. Insulin amyloid has been observed with every mode of therapeutic insulin administration (infusion, injection and inhalation), and the number of reported cases has increased significantly since 2002. The new cases represent a much broader demographic, and include many patients who have used exclusively human insulin and human insulin analogs. The reason for the increase in case reports is unknown, but this review explores the possibility that changes in patient care, improved differential diagnosis and/or changes in insulin type and insulin delivery systems may be important factors. The goal of this review is to raise key questions that will inspire proactive measures to prevent, identify and treat insulin amyloid. Furthermore, this comprehensive examination of insulin amyloid can provide insight into important considerations for other injectable drugs that are prone to form amyloid deposits.

Injection Technique and Pen Needle Design Affect Leakage From Skin After Subcutaneous Injections

BACKGROUND

After a subcutaneous injection fluid might leak out of the skin, commonly referred to as leakage or backflow. The objective was to examine the influence of needle design and injection technique on leakage after injections in the subcutaneous tissue of humans and pigs.

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.

Importance of ancillary supplies for subcutaneous immunoglobulin infusion: management of the local infusion site

A number of ancillary supplies are used in the process of administering subcutaneous immunoglobulin. The particular type of ancillary supplies used (needles, tubing, and tape) may contribute to the development of issues at the local infusion site. Patient case studies demonstrate that changes in the choice of ancillary supplies can often alleviate these issues. The use of alternative ancillary supplies should be considered prior to the possibility of changing immunoglobulin replacement products in patients experiencing local infusion-site issues in order to improve outcomes and increase compliance. A treatment progression algorithm of ancillary supply adjustments has been developed.

Injection device-related risk management toward safe administration of medications: experience in a university teaching hospital in The People's Republic of China

The use of injection devices to administer intravenous or subcutaneous medications is common practice throughout a variety of health care settings. Studies suggest that one-half of all harmful medication errors originate during drug administration; of those errors, about two-thirds involve injectables. Therefore, injection device management is pivotal to safe administration of medications. In this article, the authors summarize the relevant experiences by retrospective analysis of injection device-related near misses and adverse events in the Second Affiliated Hospital of Zhejiang University, School of Medicine, Zhejiang University, People’s Republic of China. Injection device-related near misses and adverse events comprised the following: 1) improper selection of needle diameter for subcutaneous injection, material of infusion sets, and pore size of in-line filter; 2) complications associated with vascular access; 3) incidents induced by absence of efficient electronic pump management and infusion tube management; and 4) liquid leakage of chemotherapeutic infusion around the syringe needle. Safe injection drug use was enhanced by multidisciplinary collaboration, especially among pharmacists and nurses; drafting of clinical pathways in selection of vascular access; application of approaches such as root cause analysis using a fishbone diagram; plan–do–check–act and quality control circle; and construction of a culture of spontaneous reporting of near misses and adverse events. Pharmacists must be professional in regards to medication management and use. The depth, breadth, and efficiency of cooperation between nurses and pharmacists are pivotal to injection safety.

Analysis and perspective: comparison of insulin diluent leakage post-injection using two different needle lengths and injection volumes in obese patients with type 1 or type 2 diabetes mellitus

The effects of needle gauge and length on the efficacy and tolerability of insulin injection therapy are becoming better understood. This analysis discusses some of these effects and comments on a new study by Ignaut and Fu in this issue of Journal of Diabetes Science and Technology on the effects of needle length on insulin diluent leakage from injection sites.