An injection solution is a sterile parenteral preparation, typically aqueous and occasionally oily, intended for direct administration by injection. Injection solutions are given intravenously, intramuscularly, or subcutaneously. They usually consist of one or more active ingredients dissolved in a suitable vehicle, together with excipients such as stabilizers or buffering agents.
In multi-dose containers, additional antimicrobial preservatives may be included; however, single-dose injection solutions and large-volume infusions typically rely on sterile manufacturing and suitable packaging to ensure product safety. Because the product is a liquid administered directly into the body, very high demands are placed on the hygienic and sterile packaging. According to pharmacopoeial requirements, solutions for injection must be clear and practically free from visible particles, comply with strict limits for sub-visible particles, be highly pure, and generally isotonic.
Depending on the fill volume, parenteral products are broadly categorized into small-volume parenterals (SVPs, injection solutions with volumes of up to approximately 100 mL) and large-volume parenterals (LVPs, infusion solutions with larger volumes).
SVP vs. LVP in Injections
Due to their rapid onset of action, injections are widely used in medicine today. Additionally, injection bypasses the digestive tract, allowing for a precise dosage of active ingredients. In practice, physicians differentiate between SVP (Small Volume Parenterals) and LVP (Large Volume Parenterals).
SVP doses range from a few milliliters up to about 100 milliliters. Typical applications for SVP injections are vaccines, painkillers, and antibiotics. They are usually provided as single or multi-dose preparations, for example, in ampoules, vials with rubber stoppers, or pre-filled syringes. While ampoules and vials are often drawn up with a syringe, pre-filled syringes are designed for direct administration and simplify handling in clinical practice.
LVP doses contain larger volumes, typically 250 to 1000 milliliters. They are usually administered as infusions, where the liquid is delivered intravenously via a sterile needle (commonly referred to as a “drip”) or a catheter over a specified period. Infusion solutions are typically packaged in polyolefin or PVC bags (also known as infusion bags) or BFS bottles, and less frequently in borosilicate glass bottles. Typical infusion solutions include saline, electrolyte solutions, glucose infusions, and vitamin infusions. In addition to drug delivery, they also serve to supply fluids.
The Requirements for Injection Solutions Are High
The requirements for product safety and shelf life of any injection solution are particularly high. On the one hand, the preparation is administered directly into the body, so any contamination poses a serious health risk. On the other hand, the liquid medium is susceptible to microbial contamination.
This leads to stringent requirements for sterility, freedom from particles and pyrogens throughout the entire process – from manufacture of the active ingredients through formulation of the injection solution to filling, storage, and distribution. Injection and infusion solutions must be chemically and physically stable and must not change significantly over their shelf life. Wherever possible, injection solutions – and especially large-volume infusion solutions – are formulated without added antimicrobial preservatives, because large volumes administered directly into the bloodstream can increase the risk of adverse reactions. For multi-dose injection solutions, however, suitable antimicrobial preservatives at low concentrations may be necessary to ensure microbial safety after first opening. Where terminal sterilization is not feasible, for example, with heat-sensitive products, aseptic processing must be robustly validated, including sterile 0.22-µm filtration, demonstrated container-closure integrity (CCI), and consistent environmental and process monitoring.
The BFS process (Blow-Fill-Seal) combines forming, filling, and sealing into a single, fully integrated process step. This reduces manual intervention and exposure time, thereby further minimizing the risk of contamination.
Lastly, there are also practical medical requirements, such as dose accuracy and compatibility with application systems.
Manufacturing of Injection Solutions
Only high-purity raw materials are used in the manufacture of injection and infusion solutions. Production itself takes place under aseptic, hygienic conditions. Modern pharmaceutical production facilities often rely on a continuous process. The BFS process (Blow-Fill-Seal) allows complete production of injection solutions in a single step. In BFS, containers are formed, filled aseptically, and hermetically sealed.
Production is typically followed by analytics, and if the product is stable, terminal sterilization, after which distribution occurs. Shelf life varies depending on the chemical and physical stability of the preparation, as well as storage conditions. While standard infusions, such as saline solutions, are typically stored at room temperature, many injection solutions, including vaccines, require refrigeration and protection from light.
Examples of Injection Solutions
Parenteral injections are a medical standard. Alongside tablets and oral solutions, they form an equally widespread group of pharmaceuticals. Almost everyone has had contact with injections. They are most commonly used as electrolyte solutions, nutrient solutions, local anesthetics, and as a vehicle for dissolved antibiotics.
Injection and Infusion Solutions as a Special Dosage Form
Unlike tablets, the active ingredient in an injection solution or infusion solution is dissolved in a liquid matrix. This makes storage and packaging more demanding. The primary packaging must protect the contents against light, oxygen, and microbial contamination, while not releasing any foreign substances into the injection solution. Due to the parenteral route of administration, it is also crucial that injection and infusion solutions are packaged as free as possible from particles and air. Handling plays an equally important role – for physicians and medical staff, the injection solution must be easy, safe, and quick to use at the point of care. In addition, many countries have specific regulations governing the storage, labeling, and filling of pharmaceuticals, including injection and infusion solutions.