Standard Compounded Liquid Vancomycin: The 14-Day Rule
For a majority of patients, oral vancomycin is prepared by a pharmacist using a powder form, which is then mixed with a diluent. This is known as an extemporaneously compounded or reconstituted solution. For these preparations, the guidance is clear and consistent across multiple reputable sources:
- Refrigerated Storage: The solution must be kept in the refrigerator at a temperature between 2°C and 8°C (36°F to 46°F).
- Beyond-Use Date (BUD): The beyond-use date is set at 14 days from the time of mixing. This is the maximum amount of time the medication is considered potent and safe to use. After 14 days, any unused portion must be discarded.
- Visual Inspection: Before each use, visually inspect the liquid. If it appears hazy, cloudy, or contains visible particles, it should be discarded immediately, even if it is within the 14-day window. This indicates a potential loss of physical stability.
The 14-day limit is a standard practice based on established stability data for these types of preparations. Deviating from these storage instructions can lead to a loss of potency and a risk to patient health.
Extended Stability for Commercial Preparations
In recent years, commercially available oral solutions, such as FIRVANQ (vancomycin hydrochloride), have been developed to address the limitations of compounded versions, such as a short shelf-life and potential issues with taste and consistency. Research on these specific formulations has shown promising results for extended stability.
- FIRVANQ Stability: A study found that FIRVANQ was stable for up to 30 days, regardless of storage container. This was a significant improvement over traditional compounded liquids, reducing waste and increasing patient convenience.
- Study on Longer Stability: A separate study comparing compounded solutions made from pure active pharmaceutical ingredient (API) and commercial injectable powder showed even more extended stability under refrigeration. It demonstrated that refrigerated solutions could maintain potency and physical stability for up to 90 days. For compounded solutions stored at room temperature, stability was much shorter, lasting only around 30 days before significant degradation occurred. This highlights that stability can vary by the specific formulation and compounding process used.
The Critical Role of Temperature and Formulation
Temperature is the single most important factor influencing the stability of liquid vancomycin. Vancomycin degrades more quickly in warmer environments through a hydrolytic process.
- Refrigeration (2°C-8°C): This is the ideal storage condition for all forms of oral liquid vancomycin, as it significantly slows down the degradation rate and extends the shelf life.
- Room Temperature (~25°C): Storing at room temperature can cause faster degradation. Studies have shown significant loss of potency and physical instability, such as precipitation, in preparations kept at room temperature over extended periods. For most compounded preparations, room temperature storage is not recommended beyond a very short duration, if at all.
Another crucial element is the formulation itself. The pH of the solution plays a key role in stability. Oral vancomycin has a low pH, typically between 2.0 and 4.0, but unbuffered formulations can experience a pH increase over time, leading to precipitation. Some newer compounded formulations use buffering agents to maintain a stable pH, thereby improving overall stability.
Comparison of Liquid Vancomycin Stability
| Feature | Compounded Oral Solution (From powder) | Commercial Oral Solution (e.g., FIRVANQ) |
|---|---|---|
| Preparation | Mixed by a pharmacist from powder and diluent. | Pre-formulated commercial product. |
| Storage Temperature | Refrigerated (2-8°C) is required. | Refrigerated (2-8°C) is recommended. |
| Beyond-Use Date | 14 days. | Up to 30 days (per FIRVANQ study). |
| Room Temperature Stability | Not recommended; rapid degradation (days to a few weeks). | Longer than compounded versions, but still limited (~30 days). |
| Palatability | May require flavoring at the time of administration. | Often pre-flavored to improve taste. |
| Waste Reduction | Higher potential for waste due to shorter BUD. | Lower potential for waste due to longer BUD. |
Important Safety Considerations
- Follow Directions Carefully: Always adhere strictly to the storage instructions provided by your pharmacist or on the product label. Do not assume all liquid vancomycin preparations are the same.
- Check for Changes: Before each dose, shake the bottle well and check for any physical changes, such as cloudiness, haziness, or particles. If you see anything unusual, discard the medication.
- Ask Your Pharmacist: When in doubt, consult your pharmacist. They can provide specific beyond-use date information for the exact product they dispensed to you. Given the variability in preparation, professional guidance is invaluable. The American Society of Health-System Pharmacists (ASHP) provides detailed guidance on drug stability and proper handling of medications like vancomycin.
- Keep Away from Children: As with all medications, keep liquid vancomycin safely out of reach of children, especially since it is stored in the refrigerator.
In conclusion, the short shelf life of standard compounded liquid vancomycin, typically 14 days under refrigeration, contrasts with some commercially prepared oral solutions that can last longer. However, regardless of the formulation, refrigerated storage is the most important factor for maintaining potency and preventing degradation. Patient safety is paramount, and understanding these storage requirements is essential for effective treatment.
