Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Hannah ingested 1/8th of a 200mg Advil (ibuprofen) pill. That would be 25mgs ingested.
At 4.5 pounds pounds she is about 2kgs, (4.5lbs/2.2lbs per kg) so she ingested about 12.5 mgs per kilogram of body weight (25mg/2kg = 12.5mg/kg) which is under a toxic amount.
From the ASPCA database:
◾25-125mg per kg of body weight – symptoms include vomiting, diarrhea, abdominal pain, loss of appetite, stomach ulcers;
◾more than 175mg per kg of body weight – the above symptoms plus blood in the stools, acute kidney failure;
◾more than 400mg per kg of body weight – the above symptoms plus seizures, coma, disorientation;
◾more than 600mg per kg of body weight – death.
Given the amount she ate I don't think you need to do anything as far as inducing vomiting, or worry about true toxicity with this one time ingestion. You might see mild gastrointestinal upset if she is especially sensitive, but that should be it.
At home now to try and decrease acid production in her stomach and lessen any possible symptoms you can give either:
1) Pepcid ac (famotidine) at ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 12 hours (one quarter of a 10mg tab for her)
2) Prilosec (omeprazole) at ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 24 hours (one quarter of a 10mg tab for her)
These are acid reducers that are found over the counter at the drug store. They can be given as needed.
If her stomach seems at all upset to decrease the symptoms you can feed her a bland diet for the next several days. A homemade bland diet is a mix of 1/3 boiled minced white skinless chicken or lean boiled hamburger and 2/3 boiled white rice mixed with some low salt chicken broth to make it easy to lap up and swallow and get in plenty of fluids. Feed small meals frequently.
Things to watch for that mean trouble include vomiting, especially blood tinged, dark, black or tarry stools, or frank blood in the stools, lack of an appetite, increased water consumption and urination. But I don't think you will see those given her weight and the amount she ate.
Please let me know if you have any further questions.