Welcome to Justanswer! I am Dr. Altman and happy to assist you both today!
So sorry to hear Libby is having these panting episodes. I would be more inclined to believe they are stress related versus pain since they are also in the car which would not be when we typically see pain causes
With her age my suspicion would be canine cognitive changes because they do most commonly occur in the evenings...
Below is more information on this condition, called canine cognitive disorder:
There are treatments for this that can help in supplement form but also in some situations medications as well.
1.) Melatonin can help with barking or increased movement at night
2.) Proneurozone which is a supplement for brain function that can help with mental clarify in senior pets. It is available through your veterinarian but also on-line at stores like amazon.com
3.) Fish oil is essential for brain function and used at higher doses to help cognitive function. For example, for your dog's size 1000 mg EPA & DHA daily. This can be a human formula
4.) Anipryl which is a medication used for cognitive function if the above options are not helping
5.) Alprazolam (xanax) is used for episodes of anxiety not controlled by conventional methods. Not intended for daily use but is effective as needed (in the diazepam or valium family)
6.) Donepezil 10 mg is a newer option used in human Alzheimer’s patients and is receiving attention by some veterinarians for cognitive dysfunction that we see in dogs as well as in humans. The dose ranges from 10-30 mg (1.5 mg/kg average) daily
These are all methods that your veterinarian would have available to you to assist with some of the cognitive issues and some that you should be able to purchase at a local vitamin store or on-line
I hope the above options are helpful to you but if I can assist with clarifying anything or guiding any further questions you might have please don't hesitate to ask. You certainly can see if the panting does resolve with pain medication on a trial basis of a week or so and if there is no change then consider the above. I am online another 15 minutes if I can assist with additional questions
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