Thank you for your patience (as you can see I had a lot to type)
Now the problem with chocolate is that it can cause a range of issues. Any intoxication runs the risk of causing stomach upset (vomiting, diarrhea, appetite loss, etc) and this often is seen within 2-4 hours post ingestion. That said, the higher doses can cause later stage signs (up to 36 hours later) that can really put our dogs at risk. These include elevations of the heart and breathing rate, tremors, seizures, and collapse.
With that all in mind, at least for this 65lb dog, it is a mild intoxication. So we could see GI upset but those dangerous signs are less likely. But if the other dogs did have some, then obviously this is much more serious and we'd have a larger risk for them.
Therefore, we have a few options. Since they just had this and they are still in the wrapper (which will slow absorption), we'd want to induce vomiting now. Especially in the smaller dogs if you think they had any. To induce vomiting at home, do use the 3% hydrogen peroxide orally but make sure you are giving 2 teaspoons per 10 pounds of body weight. You can give it via dropper, syringe, turkey baster – we just want to get it in. After giving this orally, move the abdomen around or get your wee ones walking about to get things mixing. This should usually lead to vomiting. If it is unsuccessful after 10 minutes then it can be repeated twice more. And if we still have no vomiting, then you'd need to consider seeing your local vet (or ER vet) so that apomorhpine (a very strong injectable emetic) can be administered just get this out and avoid any adverse issues.
Otherwise, if we cannot get them vomiting this back up, we can block absorption by treating with activated charcoal at this stage. This is available over the counter from the pharmacy (ask for the high strength version in grams, not the one for gas since you will need a lot of these) and works by binding any remaining material in the stomach. For activated charcoal, we tend to give 1-4 grams per pound every 8 hrs. This can be mixed with food to be fed or with water to syringe feed (do note that it stains, so keep it away from white carpets/clothes). This will just limit how much is absorbed and reduce the intoxication risk here. And that may be best if you don't know who ate how much.
Finally, since GI upset is the most common adverse signs with chocolate ingestion, we do want to try to address any potential GI upset here for the next 24-48 hours. To do so, you can consider offering a light diet option for a few days. Examples of an easily digestible diet include cooked white rice with boiled chicken, boiled white fish, scrambled egg, or meat baby food (as long as its free from garlic or onion powder). Ideally, we want to offer this as small frequent meals to keep stomachs settled. Further to this, if anyone shows any signs of nausea, we can also treat with an antacid. Common OTC options we can use here would be Pepcid (More Info/Dose @ http://www.petplace.com/article/drug-library/library/over-the-counter/famotidine-pepcid) or Zantac (More Info/Dose @ http://www.petplace.com/article/drug-library/library/over-the-counter/ranitidine-hcl-zantac). These are usually given 20 minutes before offering food to allow absorption and of course you want to double check with your vet before use if anyone has any know health issues or is on any medications you haven't mentioned.
Overall, for the larger dog this is just a mild intoxication with the risk of GI upset. For the smaller dogs, this could be a real risky situation. Therefore, we'd want to take one of the above approaches now to clear out any chocolate anyone has had and avoid those adverse effects. Any struggles to do so or if you see adverse signs, and we'd want to get them to their vet for IV fluids any symptomatic care to help them through this.
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All the best,
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