I understand that Dexter ingested 27mgs of Iron.
How long ago was this?
What type of iron was this?
Iron can be toxic if eaten in large quantities, but the type of iron in the supplement will affect how much Dexter actually absorbs and one pill in most cases is unlikely to be enough to be truly toxic. Most supplements do not contain elemental iron, but rather a salt or conjugated form which is significantly less toxic and absorbable than true, elemental iron.
No clinical signs of toxicity are expected in cats ingesting less than 20 mg/kg of elemental iron. Cats ingesting between 20 and 60 mg/kg of elemental iron can develop mild clinical signs. If the cat ingests greater than 60 mg/kg of elemental iron, serious clinical signs can develop. An oral dose between 100 and 200 mg/kg is possibly deadly.
If your kitten is 5 pounds he is 2.25kgs (5lbs /2.2lbs per kg =2.25kgs). If he ingested 27mgs he ingested 12mgs per kg of body weight (27mgs / 2.25kgs =12mgs/kg). Even if he ate elemental iron he will be fine.
Iron in general is very bitter and that alone can make him nauseous, but that does NOT indicate toxicity.
But odds are that with one pill ingested he will be fine.
You might see mild stomach upset, as I said iron can make them nauseous even at nontoxic levels.
Please let me know if you have any further questions.