Thermacare heat wraps contain both iron and sodium chloride (salt) both of which are gastrointestinal irritants, so it would make sense that he would vomit from ingesting those ingredients.
The good news is that this product is oxidized iron which is poorly absorbed and he would need to eat quite a bit to get sick (more than 20mg per kilogram of body weight for minimal toxic signs), and he vomited for us which is exactly what I would have recommended as a precaution.
Continued signs of toxicity are low blood pressure, a fast heart rate, repeated vomiting and diarrhea and weakness. So if he seems very lethargic he should be seen by a veterinarian. Very unlikely with the amount and type of iron he was exposed to but he is a little guy so worth watching him closely.
Sometimes the irritation is so severe they end up with scarring and strictures inside the esophagus or intestines so we need to decrease the irritation.
At home you can give either:
1) Pepcid ac (famotidine) at ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 24 hours
These acid reducers should help him feel better and decrease the chance of severe irritation. I would use them for a couple weeks.
If he has stopped vomiting for a 4-6 hours then feed him small meals of a bland diet for the next couple of days to dilute out the effects. A homemade bland diet consists of 1/3 boiled minced white skinless chicken and 2/3 boiled white rice. Feed this for several days and if all seems well then slowly start mixing in his regular diet, a little more at each meal. It should take about a week to convert him back once you start.
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