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Ferrous Sulfate

By Rania Gollakner, BS, DVM, MPH

Medications

What is ferrous sulfate?

Ferrous sulfate (brand names: Fer-In-Sol®, Feosol®) is a nutritional supplement used in cats and dogs to treat iron-deficiency anemia or as an iron supplement, usually in cases of chronic blood loss or during epoetin or darbepoetin therapy.

Dietary supplements are substances that can be used to supplement the diet, such as vitamins, minerals, amino acids, herbs, botanicals, enzymes, and probiotics. While many supplements are sold over the counter, they still contain ingredients that have biological effects that should be managed by your veterinarian. Follow your veterinarian’s directions and cautions very carefully as their directions may be significantly different from those on the label.

There are differences in how countries regulate supplements. In the United States, these substances are not as vigorously regulated by the FDA as other medications, which means they can be sold without the manufacturer proving their effectiveness, safety, and without a guarantee of consistent or accurately reported ingredients. In Canada, products that have been evaluated for quality, safety, and effectiveness by Health Canada and authorized for sale will have a license number on the label.

How is ferrous sulfate given?

Ferrous sulfate is given by mouth in the form of a tablet, liquid elixir, or liquid drops. It can be given with or without food, but it is better given with food to prevent stomach upset. If stomach upset occurs when dosed on an empty stomach, give future doses with food. Be sure not to give this mediation with dairy or cheese products. Dose liquid forms carefully.

This medication should take effect within 1 to 2 days; however, effects may not be visibly obvious and therefore laboratory tests may need to be done to evaluate this medication’s effectiveness.

What if I miss giving my pet the medication?

If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

The most common side effect is gastrointestinal upset such as discomfort, constipation, nausea, vomiting, and diarrhea. Serious side effects include blood in the stools (which may appear as black, tar colored feces) or blood in the vomit.

This moderate-acting medication should stop working in a few days, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

Do not use ferrous sulfate in pets that are allergic to it. It should be used cautiously in pets with certain blood disorders including hemolytic anemia, hemosiderosis, or hemochromatosis and in pets with gastrointestinal ulcers. It should be used with mild caution in pregnant or lactating animals, although its use is likely safe.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with ferrous sulfate: antacids, calcium supplements, chloramphenicol, fluoroquinolones, H2-receptor antagonists, penicillamine, proton-pump inhibitors, tetracyclines, or vitamin C. Vitamins, herbal therapies, and supplements have the potential to interact with each other, as well as with prescription and over the counter medications. It is important to tell your veterinarian about any medications (including all vitamins, supplements, or herbal therapies) that your pet is taking.

Large doses can also affect certain stool blood tests, and cause false positives.

Is there any monitoring that needs to be done with this medication?

Complete blood counts, blood iron levels, and total iron binding capacity will be monitored by your veterinarian. Your veterinarian may monitor your pet to be sure that the medication is working. Monitor your pet at home for serious side effects.

How do I store ferrous sulfate?

Store the tablets at room temperature between 59°F to 86°F (15°C and 30°C), and store the liquid forms at room temperature between 68°F and 77°F (20°C and 25°C). Protect from light and moisture.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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