SOURCES

Numerous products contain iron in some form, but the more soluble salt forms of iron pose the greatest risk of toxicosis. This type of soluble iron is commonly found in numerous over-the-counter multivitamin-mineral preparations, gestational iron supplements, and some fortified lawn and garden fertilizers. Because dietary or nutritional supplements are often sugar coated, dogs may eat large numbers of tablets. In addition, pet owners frequently think that vitamin or mineral supplements are not dangerous and leave this type of material in locations where animals can gain easy access. Although many other products contain iron in some form, its solubility is often so low that toxicosis would not occur. For example, metallic iron and ferric oxide (rust) are so poorly soluble that they are not considered a threat for a toxic ingestion. This type of insoluble iron may be the type found in some fertilizers, so identification of the iron form is important.

TOXIC DOSE

The dose of iron necessary to induce an iron toxicosis in the dog follows that reported for humans.¹ Ingestion of less than 20 mg/kg is generally not a threat for systemic intoxication, although a mild gastric upset may occur. With ingestion of 20 to 60 mg/kg, a mild to moderate intoxication can be expected. Ingestion of more than 60 mg/kg is a serious threat for severe intoxication. Without early intervention, ingestion of greater than 100 mg/kg is potentially fatal.

However, these toxic doses are based on soluble, bioavailable forms of iron and would greatly overestimate the toxicity of an insoluble iron form.

In evaluating the potential for toxicosis, one must calculate the amount of elemental iron ingested. This is accomplished by multiplying the amount of the iron salt (mg) by the percentage of elemental iron (0.10 for 10%). Table 50-1 lists the more common salt forms of iron and their relative percentages of elemental iron. For tablet ingestions, this information will provide the amount of elemental iron per tablet because most tablets are labeled with the amount of iron salt per tablet. Because iron ingestion can be underestimated if the label lists elemental iron instead of iron salt, one must be certain about whether the amount of iron is listed as the elemental or salt form. In addition, the ferrous salt forms of iron are more bioactive and more rapidly absorbed, but their overall toxicity is more dependent on the total soluble concentration of elemental iron.

Table 50-1 Percentage of Elemental Iron in Common Soluble Iron Salts