When preparing medications that require dilution or reconstitution for injection, the choice of diluent is a safety concern. These sterile liquids are used to dissolve powdered or concentrated drug compounds, making them suitable for administration via routes like intramuscular or subcutaneous injection. Following the correct storage protocol for these diluents is important for maintaining their sterility and the efficacy of the medication mixture. Proper handling and temperature control help ensure that the solution remains safe and effective for its intended multi-dose use.
What is Bacteriostatic Water
Bacteriostatic Water for Injection, commonly referred to as BW, is a sterile, non-pyrogenic aqueous solution designed for multi-dose use in a medical setting. Its primary function is to serve as a diluent or solvent for various injectable medications, which are often provided in a concentrated or lyophilized (freeze-dried) powder form. The solution is prepared by sterilizing purified water and then incorporating a specific chemical agent to prevent microbial growth. This key difference distinguishes it from plain Sterile Water for Injection, which contains no preservative and is intended only for single-use applications. Because BW includes a preservative, it can be accessed multiple times through its rubber stopper, offering convenience for drug regimens requiring repeated injections.
Storage Guidelines for Sealed Vials
Before a bacteriostatic water vial is punctured, its storage requirements are relatively straightforward, focusing on maintaining the integrity of the seal and the solution. Unopened vials are designed to be stable at controlled room temperature, typically ranging from 15°C to 30°C (59°F to 86°F). This temperature range preserves the chemical stability of the preservative agent within the water until the manufacturer’s expiration date. It is important to keep the vial protected from environmental extremes like direct sunlight, excessive heat, or freezing. Exposure to high temperatures can compromise the integrity of the preservative, while freezing could damage the container, risking contamination.
Storage Guidelines After Opening
The question of whether bacteriostatic water must be refrigerated becomes relevant only after the vial has been accessed for the first time. Once the rubber stopper is penetrated by a needle, the vial is no longer considered sealed, and a strict timeline begins for its safe use. The industry standard, often mandated by regulatory bodies like the U.S. Pharmacopeia, is the 28-day rule for multi-dose vials.
This guideline means that regardless of how much liquid remains, the vial must be discarded 28 days after the initial puncture. The presence of the bacteriostatic agent is what allows for this extended usage window, as it inhibits the growth of bacteria that might be introduced during repeated withdrawals. However, the efficacy of this preservative declines over time, and repeated needle insertions always carry a small risk of introducing contaminants that the preservative may eventually fail to counteract.
While the bacteriostatic agent is generally sufficient to maintain sterility at room temperature for the 28-day period, refrigeration is often advised as an extra safeguard. Storing the opened vial at refrigerator temperatures, typically between 2°C and 8°C (36°F and 46°F), helps slow down the metabolic activity of any potential microbial contaminants. Some studies suggest that refrigeration significantly reduces the risk of bacterial proliferation compared to storage at warmer room temperatures.
An additional consideration is the stability of the drug that has been reconstituted using the bacteriostatic water. Many powdered medications that are mixed with BW have their own, often stricter, refrigeration requirements to maintain their chemical potency. Therefore, while the bacteriostatic water itself may not strictly require cold temperatures to remain sterile, refrigerating the opened vial often aligns with the storage needs of the final drug product. To ensure safety, it is best practice to label the vial with the date of the first use and to follow the most conservative storage recommendation, which frequently includes refrigeration for the opened container.
The Role of Benzyl Alcohol in Preservation
The ability of bacteriostatic water to be used multiple times is due entirely to the inclusion of the preservative agent, Benzyl Alcohol (BA). This substance is typically added at a concentration of 0.9% (9 mg/mL) to the sterile water. Benzyl Alcohol functions by exhibiting a bacteriostatic effect, which means it inhibits the growth and reproduction of most bacteria.
This action is distinct from a bactericidal agent, which actively kills bacteria. The 0.9% concentration is carefully formulated to be effective as a preservative without being toxic when injected in the small volumes used for drug reconstitution. The presence of BA creates an environment where any bacteria introduced during needle punctures cannot proliferate rapidly. The 28-day rule serves as a safety margin because the efficacy of the Benzyl Alcohol gradually diminishes over time and with repeated exposure to air.