Hello, get a new bag and start infusing again if there are a significant amount of crystals. I recommend getting a new bag since the mannitol is crystalizing = necessary drug that is now no longer available to give to the patient. Perhaps withdraw the amount already infused from the new bag before starting, or set your IV pump to only infuse the remainder that would be needed.
Many times to reduce chance of crystallization I will convert orders from 25% to 20% mannitol, but it can still happen.
Ensure you always infuse mannitol through a filter (usually a filter needle which is 5 micron in size is adequate) in case that happens.
I agree with Alchemist’s comment, where you currently store or stock your bags of Mannitol 20% is essential also, it will be great if you have a warmer in your pharmacy department to prevent that from happening.
Usually mannitol crystalize when exposed at lower temperature especially at higher concentrations so if it is prior administration , you shall warm it to 37°C and followed by gentle agitation but if it is happened during administration so in this case you shall change the bag and you need to use always inline filter