Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your pup has eaten some garlic.
Onions and garlic can be toxic for dogs because they cannot digest them properly leading to nausea, vomiting, abdominal pain and cramping, red blood cell damage, anemia and secondary organ damage.
The toxicity is dose dependent however. That means that a dog must eat a certain amount of onions or garlic per pound of body weight to see signs of toxicity. They must eat 0.5% of their body weight of onions in order to see toxic effects. In a 20 pound dog that is 0.1 pounds (20lbs X 0.005 = 0.1) or 1.6 ounces (16 ounces X 0.1 = 1.6 ounces) of onions.
Garlic is more toxic then onions as it has more concentrated toxins. But the toxic amount is variable between different cloves of garlic, so all we can say is we know that if he ate more than 1.6 ounces of garlic it will likely cause symptoms of toxicity.
Do you think that he ingested that amount of garlic?
Activated charcoal will bind drug or chemical toxins, but it must be given within a period of time in order to work. If you want to give it a try he will need 1 GRAM per pound of body weight or 20 GRAMS (not milligrams). If it has been more than 18-24 hours it is likely too late to give activated charcoal.
It can take several days (2-5 days) or in some cases as long as a week to see symptoms. Symptoms range from vomiting and diarrhea to severe abdominal pain, lethargy, icterus (yellow gums and skin, and whites of his eyes), panting, difficulty breathing, fast heart rate and weakness, possibly progressing to death if he isn't treated.
Once clinical signs develop, supportive care including intravenous fluids (to keep him hydrated) and oxygen therapy are the main forms of treatment. Some dogs may require a blood transfusion if their red blood cells are damaged enough.
The outlook for onion toxicity is good with early treatment but “guarded” in severe cases or in dogs that are not treated by a veterinarian.
If he seems apparently normal still tonight then I would plan on having him seen tomorrow by his veterinarian for an examination and some blood tests, and possibly retesting in a few days if he seems ok tomorrow. We do need to keep a close eye for several days before we can be sure he will be OK.
Please let me know if you have any further questions.