Thanks for the answers to my questions and additional information.
As I understand it, this product contains three ingredients: camphor, menthol and methyl salicylate.
Menthol isn't typically too much of a problem but the other two potentially might be.
Camphor can cause oral irritation (even corrosive injury) as well as vomiting/diarrhea if in a high enough concentration (usually greater than 6-11% as listed on the label); I believe the percentage is listed at about 3 % for Pain a Trate so I wouldn't expect significant issues.
Methyl Salicylate is an aspirin product and, again, if sufficient amounts are eaten can cause gastric issues as well as vomiting/diarrhea. I wouldn't consider the amount he ate to be a toxic one but it might cause some problems with this gastrointestinal tract which wouldn't be seen for another few hours (if at all).
Having said the above, more than likely, he'll be just fine in terms of any significant side effects, but you still have a window of opportunity to induce vomiting if you have 3% hydrogen peroxide so you don't have to worry about any potential issues.
The dose would be 2 tablespoons mixed with bread, walk him around and repeat the dose in 15 minutes if necessary. Not all dogs vomit when peroxide is given but most will.
If you don't have peroxide and/or decide not to induce vomiting, then I'd give him over the counter Pepcid AC (Famotidine) at a dose of 10 mg twice a day for a few days.
Another option would be Prilosec (Omeprazole) at a dose of 10 mg once a day.
If diarrhea develops, then a bland diet of boiled chicken and rice should resolve the problem within a day or so.
I hope this helps and that he'll be just fine (which more than likely he will be).