Ferrous Sulfate
Iron (II) sulfate
Also known as: Fer-In-Sol · Feosol · FeroSul · Fer-Gen-Sol · eisen(II)-sulfat · ferreux (sulfate) · ferrosi sulfas heptahydricus · ferrous sulphate · ferrum sulfuricum oxydulatum · iron (II) sulphate heptahydrate · iron sulphate · ferrous sulfate, exsiccated · dried ferrous sulfate
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Iron deficiency anemia | 100-300 mg (total dose) PO once a day | PO | q24h | — | 🌎 NA |
| Iron deficiency anemia | 100-300 mg per day (total dose) PO | PO | q24h | — | 🌎 NA |
| Adjunct to epoetin (erythropoietin) therapy | 100-300 mg (total dose) PO per day | PO | q24h | — | 🌎 NA |
- Iron deficiency anemia: Dose is for ferrous sulfate, not elemental iron.
- Iron deficiency anemia: First correct underlying cause of blood loss. Absorption is enhanced if administered 1 hour before or several hours after feeding. Reduce dosage if GI side effects occur.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Iron deficiency anemia | 50-100 mg (total dose) PO once daily | PO | q24h | — | 🌎 NA |
| Iron deficiency anemia | 30-200 mg (total dose) PO per day | PO | q24h | 2 weeks or more | 🌎 NA |
| Adjunct to epoetin (erythropoietin) therapy | 50-100 mg (total dose) PO per day | PO | q24h | — | 🌎 NA |
| Adjunct to epoetin (erythropoietin) therapy | 5-50 mg per cat PO once daily | PO | q24h | — | 🌎 NA |
| Adjunct to epoetin (erythropoietin) therapy | 50-100 mg per cat PO once daily | PO | q24h | — | 🌎 NA |
| Adjunct to epoetin (erythropoietin) therapy | 10 mg/kg PO once daily | PO | q24h | — | 🌎 NA |
- Adjunct to epoetin (erythropoietin) therapy: Many cats do not tolerate oral iron therapy and are better treated with iron dextran at 50 mg IM q3-4 weeks.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Hematinic | 2-8 g PO per day | PO | q24h | 2 weeks or more | 🌎 NA |
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Hematinic | 8-15 g PO per day | PO | q24h | 2 weeks or more | 🌎 NA |
Swine
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Hematinic | 0.5-2 g PO per day | PO | q24h | 2 weeks or more | 🌎 NA |
Sheep
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Hematinic | 0.5-2 g PO per day | PO | q24h | 2 weeks or more | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Ferrous sulfate is an oral iron supplement primarily used in veterinary medicine to treat iron-deficiency anemias (most commonly secondary to chronic blood loss, such as severe flea/hookworm infestations or gastrointestinal bleeding) and as an adjunctive therapy in patients receiving erythropoietin (epoetin) for chronic kidney disease.
Clinical Pearl: Dosing oral iron can be confusing. It is critical to distinguish between the dose of the iron salt (ferrous sulfate) and the dose of elemental iron. Regular ferrous sulfate contains approximately 20% elemental iron (200 mg elemental iron per gram), whereas dried (exsiccated) ferrous sulfate contains approximately 30% elemental iron (300 mg elemental iron per gram).
Mechanism of action
Iron is an essential trace mineral required for the transport and utilization of oxygen.
Dietary or supplemental iron is absorbed primarily in the duodenum and proximal jejunum → binds to the transport protein transferrin in the plasma → transported to the bone marrow → incorporated into porphyrin to form heme.
Heme is a critical component of hemoglobin (in red blood cells) and myoglobin (in muscle). Ionized iron also acts as an essential cofactor for several metabolic enzymes, including cytochrome oxidase, succinic dehydrogenase, and xanthine oxidase. While iron does not directly stimulate erythropoiesis, it provides the necessary building blocks to correct hemoglobin deficits caused by iron deficiency.
Safety & warnings
Contraindications
- Hemosiderosis
- Hemochromatosis
- Hemolytic anemias
- Known hypersensitivity to iron products
- Gastrointestinal ulcerative diseases (relative contraindication due to GI irritation)
Adverse effects
- Mild gastrointestinal upset (nausea, vomiting)
- Black or dark-colored feces (normal and harmless)
- Constipation or diarrhea
Precautions
WARNING: Dosing of oral iron products can be confusing. Always verify whether the dose is for the iron salt (e.g., ferrous sulfate) or elemental iron. Use with caution in patients with GI ulcerative diseases due to the irritating properties of the drug. Large doses can color feces black, causing false-positives on guaiac tests for occult blood.
Drug interactions
May bind to iron and decrease oral absorption; administer at least two hours apart.
May bind to iron and decrease oral absorption; administer at least two hours apart.
May delay the response to iron administration; avoid using in patients with iron deficiency anemia.
Iron may significantly reduce the absorption of oral fluoroquinolones; administer at least two hours apart.
Increased gastric pH may decrease iron absorption.
Iron can decrease the efficacy of penicillamine by decreasing its absorption; space doses as far apart as possible.
Increased gastric pH may decrease iron absorption.
Oral iron preparations can bind to orally administered tetracyclines, decreasing the absorption of both compounds.
Iron may reduce the absorption of oral thyroxine; administer at least two hours apart.
May enhance the gastrointestinal absorption of iron.
Monitoring
- Clinical efficacy (resolution of anemia signs)
- Hemograms (CBC)
- Serum iron (Normal: Dogs 80-180 mcg/dL, Cats 70-140 mcg/dL)
- Total iron binding capacity (TIBC) (Normal: Dogs 280-340 mcg/dL, Cats 270-400 mcg/dL)
- Serum transferrin saturation
Pharmacokinetics
Absorption
Complex and determined by diet, iron stores, erythropoiesis degree, and dose. Absorbed throughout the GI tract, but mostly in the duodenum and proximal jejunum. Food in the GI tract may reduce the amount absorbed.
Distribution
After absorption, ferrous iron is immediately bound to transferrin and transported to the bone marrow.
Metabolism
Incorporated into hemoglobin. Iron metabolism occurs in a nearly closed system; iron liberated by hemoglobin destruction is reused by the body.
Elimination
Only small amounts are lost via hair and nail growth, normal skin desquamation, and GI tract sloughing.
Overdose
Ingestion of iron-containing products can result in life-threatening toxicity. As little as 400 mg of elemental iron can be fatal in a child.
Clinical Signs of Toxicity:
- Phase 1 (30 mins to several hours): Acute gastrointestinal irritation, distress, vomiting (possibly hemorrhagic), abdominal pain, and diarrhea.
- Phase 2 (12-48 hours): The patient may appear asymptomatic, but this can be a deceptive latent phase.
- Phase 3: Peripheral vascular collapse, hypotension, cyanosis, pulmonary edema, fulminant hepatic failure, coma, and death.
- Long-term Sequelae: Animals that survive may exhibit gastric scarring, strictures, and persistent digestive disturbances.
Treatment:
- Must be handled as an absolute emergency.
- Decontamination: Empty the stomach using gastric lavage with a large bore tube (avoid emetics if hemorrhagic vomiting is already present). Lavage with tepid water or 1-5% sodium bicarbonate solution.
- Oral milk of magnesia may help bind the drug in the GI tract.
- Antidote: Deferoxamine is a specific chelating agent used to bind absorbed iron.
- Supportive Care: IV fluids for shock, treatment of acidosis, prophylactic antibiotics, oxygen, and management of coagulation abnormalities or seizures.
Available products
Formulations
- Oral Tablets
- Oral Elixir/Liquid
- Oral Drops
Veterinary
- No single-ingredient veterinary-FDA-approved products are available. Many multivitamin products containing iron are available.
Human-labeled
- Ferrous Sulfate Oral Tablets: 325 mg (65 mg iron)
- Ferrous Sulfate Oral Elixir/Liquid: 220 mg/5mL (44 mg iron/5 mL), 300 mg/5 mL (60 mg iron/5 mL)
- Ferrous Sulfate Oral Drops: 15 mg iron/mL, 75 mg/0.6 mL (15 mg iron/0.6 mL)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store in tight, light-resistant containers. If exposed to moisture or moist air, the drug is rapidly oxidized to a brownish-yellow ferric compound that should not be used medicinally. Exposure to light or an alkaline medium enhances this conversion.
Client information
DANGER: Iron overdose is highly toxic and potentially fatal. Keep all iron supplements strictly out of reach of pets and children.
- Purpose: Used to treat iron-deficiency anemia, which is often caused by chronic blood loss (e.g., severe flea or hookworm infestations, bleeding ulcers) or to support red blood cell production in pets with kidney disease.
- Administration: Absorption is best on an empty stomach (1 hour before or several hours after meals). However, if it causes stomach upset or vomiting, you may give it with a small amount of food.
- Side Effects: Do not be alarmed if your pet's stool turns dark black; this is a normal, harmless side effect of unabsorbed iron passing through the digestive tract.
- Interactions: Do not give at the same time as antacids, dairy products, or certain antibiotics (like tetracyclines or fluoroquinolones). Separate doses by at least 2 hours.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.