Pain-Free Injections: Understanding Key Factors of Pain for More Tolerable Subcutaneous Administration

In the field of healthcare, injections have long been associated with a common reaction ‘Ouch!’ Whether it’s a routine vaccine or a necessary medication. Subcutaneous (SC) injections are an unavoidable but still a rather unpleasant intervention. The effects such as swelling, discomfort and pain experienced after these injections may cause patients to avoid these injections hence affecting their health. However, the advancements in the field of medical technology and understanding of pain signal processing have made injections less of a pain.

Fig 1. Key factors responsible for pain 

The pain felt during SC injections is therefore notably affected by the type of design that is adopted in these injection devices. Some of the important characteristics of the device are; the gauge or thickness of the needle, the length of the needle used, the rate of the injection, and how the injection is made. Conventional views are that thinner needles are likely to cause less pain though they may not be ideal for all types of injections. Needle length also plays an important role; long needles are comparatively less painful, but cannot penetrate up to the required depth for some of the medications. This is one of the causes of pain; devices that regulate the speed of injection will help reduce the pain. Large volumes of injections and injecting at a high rate also proved to cause tissue damage and more sensitization as compared to those, where injections are administered slowly. Modalities like auto-injectors and needle-free systems have been developed to suit these parameters, administering the medicine in a way that will cause the least amount of discomfort.

The characteristics of the injected drug determine the level of pain patients will have to endure. Some types of solutions may be more painful to inject because of the greater viscosity of the fluid. Lower viscosity formulations are typically less invasive since these formulations do not require a lot of pressure to be inserted through the needle. Some of the preservatives and excipients in drug preparations are capable of causing tissue irritation and resulting in pain and discomfort. Products that contain milder ingredients and less preservatives are less likely to cause inflammation, and therefore, are associated with minimum pain. Pain related to the formulation is reduced or eliminated by controlling and enhancing some of these properties to avoid tissue inflammation in the patient.

Fig 2. The interrelationship between device and formulation parameters

Pain is partially dependent on the mental status of a patient; Fear of injections and anxiety only amplify the sensation of pain to make it worse. Thus, the psychological aspects of injections play a significant role, and clinically relevant knowledge of them is necessary to enhance the overall injection experience. Patients may feel soreness at the injection site or use fear as a coping mechanism despite there being ways to manage such anxiety. Anxiety levels can be effectively managed by deep breathing, distraction from the procedure, and information about the process of administering the injection. Explaining to patients what they are likely to experience during the injection and the possible benefits of the medication may help in preventing these emotions from rising and preparing them for the injection.

The current development in the technology of SC injection, various methods, and techniques also hold an assurance that in the near future, injections will not cause pain and anxiety. Future studies and innovations are to design better injection systems that can sense the body structure of the patient and reduce the pain level caused by injections by having better control over other parameters. These advancements do not only offer relief from the uncomfortable feeling of injections but it even serves as a way of motivating patients to disperse with careless adherence to their prescribed medications.

Reference:

Mathias N, Huille S, Picci M, Mahoney RP, Pettis RJ, Case B, Helk B, Kang D, Shah R, Ma J, Bhattacharya D. Towards more tolerable subcutaneous administration: Review of contributing factors for improving combination product design. Advanced Drug Delivery Reviews. 2024 Apr 2:115301. https://doi.org/10.1016/j.addr.2024.115301

Image Credits:

1. Cover Image - https://www.smithsonianmag.com/innovation/needle-could-make-for-pain-free-flu-shots-180953141/
2. Fig 1 & Fig 2 - https://www.sciencedirect.com/science/article/pii/S0169409X24001236