How long does it take for a tooth infection swelling to go down, after starting antibiotics?

24 to 48 hours: You should notice an improvement within 48 hours.

It depends: It depends on severity of infection and the type of bacteria involved in the infection.

I day to 1 week: If you have the correct antibiotic it can be very quick. With the wrong antibiotic it will take a long time. Amoxicillin is good for approximately 75% of the bacteria. Adding Metronidazole (flagyl) takes that up to 99%. Augmentin (amoxicillin and clavulanate) also gets 99% of the bacteria.