What is the correct ampicillin dosage for dogs?

1ml per 100 lbs of body weight (10 pound dachshund would need 1/10th of a mL)

2nd answer-- It depends on which type of penicillin you are using, if you are talking about the Penicillin injectable 300,000 units per ml, it is dosed at 1ml per 10-20 lbs of body weight. IM or SUBQ--More commonly 1 ml per 20 pounds, given once a day, for at least 3 days. Do not exceed more than 3ml per injection site. So if you have a 100 pound dog, you should give a total of 5ml but not all in the same injection site, I'd probably do 2.5ml in one location, and then another 2.5 in a different location.