Hello, my name is***** and I have over 20 years of experience as a veterinarian. I'm sorry to hear that your fellow Bogart ingested 3000mgs of Bupropion.
Toxicity is based upon how many milligrams per pound he ingested.
The minimum toxic dose where we could possibly see signs of toxicity for Bupropion is 10 mg / kg (2.2 pounds) of body weight.
If he is 27 pounds then he is 12.27kgs (27lbs/2.2lbs per kg = 12.27)
If he ate 300mgs then he ate 24.44mgs/kg and that is above a toxic amount (10mgs per kg), so you will see signs of toxicity.
Small amounts may cause sedation and lethargy. Larger overdoses may cause salivation, agitation, ataxia, tremors, and seizures.
If this happened within the past two hours and he still seems normal I would induce vomiting by giving him 3% hydrogen peroxide at a dose of 1 tablespoon orally per 10 pounds of body weight (2 &1/2 tablespoons for a 27 pound dog) mixed with a little ice cream or bread chunks, then take him out and run him around to get the peroxide fizzing.
If no vomiting in 10 minutes repeat the peroxide dose once.
Once he vomits and clears his stomach and be done I would check to see if most or all of the pill is present.
Then to try and settle his stomach today after he vomits you can give either:
1) Pepcid-ac (famotidine) at a dose of one 10mg tablet per 20 to 40 pounds of body weight very 12 hours.
2) Prilosec (omeprazole) at a dose of one half of a 20mg tablet per 20 to 40 pounds of body weight every 24 hours.
These will reduce stomach acid and should help settle his stomach.
If he already showing symptoms it is too late to induce vomiting.
If he is just sleepy you can simply observe him closely, keeping him confined and away from stairs and off furniture so he doesn't fall and hurt himself. But if he is agitated, having tremors or seizures then I would recommend that he see a veterinarian today on an emergency basis.
Best of luck with your fellow, please let me know if you have any further questions.