Hello, my name is***** and I have over 20 years of experience as a veterinarian. I'm sorry to hear that your pup enjoyed eating some chocolate. Chocolate can be toxic for dogs but they need to eat a certain amount per pound of body weight to get sick. White chocolate is the least toxic, and milk chocolate is less toxic than dark chocolate. So he ate two of the less toxic types of chocolate.
White chocolate has so little toxins in it that I wouldn't be concerned about that except the high fat content can cause nausea, and thus may explain his vomiting.
A 20 pound pup would need to eat 3 ounces of milk chocolate to see symptoms of drooling, nausea, vomiting and diarrhea and almost 6 ounces of milk chocolate to see hyper-excitability and an elevated heart rate.
At higher amounts we can see muscle tremors and possible seizures.
I am glad to hear that he vomited, as that means much of the toxins may be out of his system, and he should do well in the long run.
In most cases of mild chocolate toxicity the toxins are out of their system in 24 to 48 hours. We generally begin to see symptoms, if they eat a toxic amount, within 4 to 6 hours, rarely it takes about 12 hours.
At this point I don't think that you have much to worry about, but I can give you symptoms to watch for now.
As a precaution once he stops vomiting I would encourage you to get him to drink as much as possible for the next 12 hours and to get him out to urinate frequently. Chocolate toxins are metabolized out through the kidneys and can be reabsorbed from the bladder so we don't want them to sit in his bladder for long.
I would with-hold food for the next 12 hours to stop intestinal spasms.
Since he is nauseous to try and settle his stomach you can give either:
1) Pepcid ac (famotidine) at a dose of 1/2 of a 10mg tablet per 10 to 20 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at a dose of 1/4 of a 20mg tablet per 10 to 20 pounds of body weight every 24 hours
These are acid reducers and should help him feel less nauseous. They are quite safe and can be used for several days if needed.
Then you can with-hold food for several hours to decrease the symptoms of stomach upset and feed him a bland diet for the next couple of days. A homemade bland diet is a mix of 1/3 boiled minced white skinless chicken or lean boiled hamburger and 2/3 boiled white rice mixed with some low salt chicken broth to make it easy to lap up and swallow. Feed small meals frequently.
If you do notice a very rapid heart rate (more than 160 beats per minute in a small dog) repetitive tremors or seizures then he should be seen by a veterinarian on an emergency basis for treatment. They can use injectable medications to control his heart rate and stop the seizures until the toxic levels fall.
I sincerely ***** ***** you are going to see any serious symptoms if you haven't seen any by now. I suspect that since he vomited he didn't ingest enough to cause a serious toxicity. I just wanted to give you things to watch for and what to do should you see any symptoms.
Best of luck with your fellow, please let me know if you have any further questions.