Hello, my name is***** and I have over 20 years of experience as a veterinarian. I understand that you are concerned about your pup Franklin chewing up and ingesting a cold pack that probably contained propylene glycol.
Propylene glycol can be toxic, but enormous quantities would have to be ingested in a bigger dog to see toxic effects. It is much less toxic than the related compound ethylene glycol responsible for antifreeze toxicity. No clinical signs were seen when a dog was given a dose of pure propylene glycol of 10 mls (2 teaspoons) per pound of body weight.
In very large amounts that are toxic quantities we can see acidosis, liver damage, and kidney damage. Clinical signs of a propylene glycol toxicity include central nervous system depression, weakness, incoordination and seizures. In the case of a large ingestion, large quantities of fluids to flush the toxin out, and supportive care, such as treatment for acidosis, should be given.
I wouldn't expect to see any problems at all other than mild stomach upset with the amount in one gel pack in a big dog. You can flush his mouth with cool water to remove any traces of it.
If he ate the covering and didn't chew it up it may cause a blockage if he ate enough of it.
If he has a sensitive stomach and you believe he may have swallowed the plastic cover in big chunks you can feed him a bland diet with added fiber. A homemade bland diet consists of 1/3 boiled, lean hamburger (or boiled, white skinless chicken), all fats and juices drained off the meat, mixed with 2/3 boiled, plain white rice. Feed several small meals a day. You might wish to add 2-4 tablespoons of canned pumpkin (not pie filling, just pumpkin) to each meal if you think he did ingest the plastic in big chunks to help increase fiber, which will help push pieces through.
Feed this food for several days and if he is doing well then gradually start mixing in his regular diet, more at each meal. It should take about a week to get him converted back.
Signs that things aren't going well, and he needs an immediate veterinary visit, are vomiting, a tense painful belly, lack of an appetite, a fever (more than 103.5F rectally) and lethargy. This could be related to the plastic pieces getting stuck.
Let me know if you have any further questions.