How long can you store injectable solution drawn in a syringe?

[dnBQByvHb8Zkawbjpx]

Low doses (<100 mg) are notoriously difficult to weigh with precision unless some very-high-precision scales are used. For example, to prepare ketamine for IM, it may be better to prepare a batch of five shots by dissolving 500 mg K in 5 ml of saline solution, instead of weighing 100 mg for one shot (which could be 150 mg due to scale error).

Consider a guaranteed sterile solution prepared by cooking K in saline. The solution is then drawn into sterile syringes using new sterile needles or 0.22 um syringe filters. The needle on each syringe is then swapped for a brand new one. How long can you store such prepared shot safely, presumably in the fridge at 4-5 °C? The aspect of the stability of K does not concern me as there are studies that did not show any degradation of K stored in syringes. I am concerned about the micro-bacterial safety of the stored shots after a week or max two weeks. Would they be safe to use?

 

[Paracelsus]

While the chemical stability of ketamine in solution is well-established, the primary issue is the potential for bacterial contamination over time, especially when storing the prepared syringes in a refrigerator.

Sterility Considerations:

1. Sterile Preparation: Using 0.22 µm syringe filters significantly reduces the risk of bacterial contamination, as they are designed to remove most bacteria. However, some viruses and smaller particles, including spores, may not be fully filtered, though this is a relatively low risk.
2. Sterile Storage: Once the solution is prepared and syringes are filled, replacing the needle with a new sterile one helps maintain sterility. Ensuring that the syringes and needles used are individually sterile and handled in a clean environment further minimizes risks.
3. Refrigeration: Storing the prepared syringes in the fridge (at 4-5°C) slows bacterial growth but does not completely stop it. Refrigeration is effective in prolonging the sterility of injectable solutions for a limited period, as most bacteria and fungi grow more slowly at lower temperatures. However, it’s not foolproof against contamination, especially over extended periods.

Microbial Safety of Stored Shots:

1. First Week: If the solution is prepared under optimal sterile conditions and stored in the refrigerator, it is generally considered safe to use for up to one week. This is within the window where bacterial contamination risk remains low, assuming no breaches in sterility during preparation or storage.
2. Second Week: Extending storage to two weeks raises the risk of bacterial contamination. Although refrigeration and the use of sterile equipment mitigate this, some opportunistic organisms can still multiply slowly in refrigerated conditions. The risk is higher after the first week, so beyond that, the safety of the solution becomes more questionable.

Continue to use sterile equipment (syringes, needles, saline, and filters) and maintain clean working conditions during preparation. Label each syringe with the preparation date to ensure safe use within the recommended timeframe.

 

[dnBQByvHb8Zkawbjpx]

Thank you for the detailed comment. I have been thinking along the same lines: filtering does not remove viruses (too small) which is why I opt for sterilization by heat at 99 °C as the primary method that sterilizes the solution.

I plan to prepare batches of no more than five shots at a time; one of them would be consumed immediately and up to four would be stored. The last of them would be used around the start of the 2nd week and I'm glad to hear my plan is not outrageously stupid and/or dangerous.

I did not have labeling each syringe in my protocol and I'll definitely do that, thank you for pointing this out.