Hello, my name is***** and I have over 20 years of experience as a veterinarian.
I understand that you are concerned about your pup ingesting iron pellets. Was it from from an oxygen absorber packet? These packets do contain reduced iron and if enough of that is ingested it can be toxic. She is a small dog at 20-25 pounds so we do need to be more concerned than if she were a big dog (like a Labrador retriever). The good news is that she only ate part of a package. Ingestions of less than 2.27mg - 9 mg/pound of body weight of elemental iron typically result in mild clinical signs but are not likely to result in significant toxicity. 9 - 27.27 mg/pound of body weight of elemental iron can cause mild to moderate signs of toxicity, and eating more than 27.27mgs per pound of body weight can lead to serious poisoning or death. Eating between 45mgs and 113mgs per pound are potentially lethal.
We assume iron-based oxygen absorbers contain 50% elemental iron. Typical sizes of oxygen scavenger sachets range from 2-30 g (net weight), so would contain 1-15grams of elemental iron. If she only ate part of a package then she is unlikely to have a truly toxic reaction, but she might still have mild stomach upset.
Toxicity can cause direct damage to the lining of her gastrointestinal tract, (leading to vomiting, diarrhea, abdominal pain, lethargy, and gastrointestinal bleeding, sometimes severe), damage to the cells in her body leading to liver damage and difficulty clotting (the liver produces clotting factors) shock, and death. Very rarely we can see strictures forming in the stomach which cause an obstruction 2-8 weeks after eating the iron.
At this point I would recommend that you give acid reducing medications to protect her gastrointestinal tract. This will reduce the amount of iron that she will be able to absorb just in case she ate more than you thought. You can give either:
1) Pepcid ac (famotidine) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 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 should be given for two weeks minimally.
If you notice diarrhea, especially if it is bloody, she should be seen by a veterinarian. If she has a tense painful abdomen, refuses to eat, or seems very lethargic she should see a veterinarian.
If you want to be extra safe even if she seems normal seeing her veterinarian Monday and checking her liver enzyme levels could be done.
Please let me know if you have any further questions.