Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your pup was given an overdose of Azithromycin.
The usual dose of Azithromycin is 2.5 to 5 mg per pound of body weight orally once daily for up to 7 days.
So your pup should have been given 262.5mgs to 525mgs once a day. She was given roughly 2 to 4 times a normal dose.
Even with a normal dose we can see nausea, vomiting, abdominal pain, and diarrhea.
I would expect with the dose she took to lead to these sorts of symptoms.
Rarely we can see liver and kidney damage with an overdose of this drug. But usually this would be with repeated high doses in a dog with pre-existing liver or kidney disease.
If you just gave this medication, within the past 2 hours, you can induce vomiting to try to remove the antibiotic.
You can give her 1 tablespoon of 3% hydrogen peroxide per 10 pounds of body weight soaked up with bread chunks, or mixed with ice cream or a little food (no more than 3 tablespoons at a time even for a pup greater than 35 pounds).
Then take her outside and run her around to get the peroxide bubbling so she vomits.
If no vomiting in 10 minutes repeat the peroxide dose once.
If she vomits and seems to clear her stomach and be done I would check to see if the evidence of the antibiotic is present.
Then to try to avoid nausea/vomiting and diarrhea feed a homemade diet of 1/3 boiled, lean hamburger or boiled, white, skinless chicken, all fats and juices drained off the meat, and 2/3 white rice.
If you don't have peroxide or she doesn't vomit you can get him to an emergency clinic to induce vomiting.
If it has been longer than 3 hours it is likely too late to induce vomiting, then just feed her the bland diet mix and watch her for signs of toxicity (severe vomiting, diarrhea, yellow color to the skin, gums, whites of the eyes).
Treatment of toxicity is based upon support for the patient's organs with fluids and treating the nausea and diarrhea that come along with it.
Please let me know if you have any further questions.