If she just had this and hasn't signs yet, we need to act fast. The chocolate dose is severe and could cause GI upset, breathing/heart rate changes and even seizures. Furthermore, with raisins as well this could damage her kidneys.
So, since we are in a risky situation, we need to intervene. To induce vomiting, you can use plain soda crystals. You just want to take a small handful, mix it with water to make a paste, roll that into a ball, and put this right in the back of the throat for him to swallow. This usually will trigger vomiting.. If it doesn't or you do not have soda crystals on hand, then you can have him seen urgently by your local ER vet so that apomorhpine (a very strong injectable emetic) can be administered just get this out of the stomach and avoid any adverse issues.
As well or alternatively, you can also use activated charcoal. 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 for 24 hours. 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.
Finally, after the above, we do want to try to offset any GI upset here for the next 24-48 hours. To do so, you can consider offering a light diet option like 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 the stomach settled. Further to this, if we see any hints of nausea, then we can also treat with an OTC antacid [ie 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 can be given every 12 hours. Of course, double check with your vet before use if your wee one has any know health issues or is on any medications you haven't mentioned.
Finally, just to note in case you were keen to have your wee one seen today, some veterinary practices in our country have office hours today. As well, I wanted to mention that most veterinary practices here do have contingency plans for emergency care for their patients even when they are not open. Therefore, it is worth ringing the practice. If they are open, you can get in today. If they aren't, then they will likely have a message to direct you on how to contact their out of hours service. And if you don't have a vet, you can find one local to you via the RCVS Register (http://findavet.rcvs.org.uk/find-a-vet/) to find your local vets or Vets Now (http://www.vets-now.com/find-an-emergency-vet/) who are open all nights/weekends. In any case, there is help here if you struggle with any of the above here for Hope.
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