The powdered capsules remain stable at room temperature (even up to about 85 degrees, 30 degrees C), and don’t require refrigeration. The commercial 50mg/ml liquid Neurontin does need to be stored in the fridge and is most stable between 36-46 degrees F (2-8 degrees C). There are some reports that it can remain stable out of refrigeration for up to 7 days at up to 85 degrees F (30 degrees C).
Essentially, if you find you left your cat’s liquid gabapentin out for a short period, like an hour or two, it’s likely not a problem. If it was left out overnight or longer, make sure to contact your vet’s office for the best advice on what to do. Liquid gabapentin left out will not become dangerous or toxic for a kitty, but may lose some of its efficacy.
If you have a compounded form of gabapentin that requires refrigeration, it’s best to contact the specific compounding pharmacy for advice if it’s left out, because requirements may differ depending on the compounding methods.