Vitamin A / D / E — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	Vitamin A: 100-500 IU/kg/day; Vitamin D: 10-50 IU/kg/day; Vitamin E: 10-20 IU/kg/day	q24h	Duration: Variable; for deficiency, until clinical signs resolve Notes: Doses vary by product; avoid excessive vitamin A and D to prevent toxicity.
Cat	PO	Vitamin A: 100-500 IU/kg/day; Vitamin D: 10-50 IU/kg/day; Vitamin E: 10-20 IU/kg/day	q24h	Duration: Variable; for deficiency, until clinical signs resolve Notes: Cats require preformed vitamin A (cannot convert beta-carotene efficiently).
Horse	PO	Vitamin A: 10,000-30,000 IU/day; Vitamin E: 1-2 IU/kg/day (up to 10 IU/kg for deficiency); Vitamin D: 500-1,000 IU/day	q24h	Duration: Variable; for deficiency, until clinical signs resolve Notes: For performance horses, higher vitamin E may be used.
Cattle	IM	Vitamin A: 30,000-60,000 IU/kg; Vitamin D: 5,000-10,000 IU/kg; Vitamin E: 1-2 IU/kg	Single dose or repeated as needed	Duration: For deficiency, repeat after 2-4 weeks Notes: Injectable formulations are available for herd treatment.
Small Ruminants	IM	Vitamin A: 10,000-30,000 IU/kg; Vitamin D: 5,000-10,000 IU/kg; Vitamin E: 1-2 IU/kg	Single dose or repeated as needed	Duration: For deficiency, repeat after 2-4 weeks Notes: Use with caution in neonates.
Rabbit	PO	Vitamin A: 5,000-10,000 IU/kg; Vitamin E: 10-20 IU/kg	q24h	Duration: Variable Notes: Vitamin D requirement is low; excessive vitamin D can cause toxicity.
Bird/Poultry	PO	Vitamin A: 5,000-10,000 IU/kg; Vitamin E: 10-20 IU/kg; Vitamin D3: 500-1,000 IU/kg	q24h	Duration: Variable Notes: Water-soluble formulations are available for flock treatment.
Reptiles	PO	Vitamin A: 100-500 IU/kg; Vitamin D3: 10-50 IU/kg; Vitamin E: 10-20 IU/kg	q24h	Duration: Variable Notes: Dust prey items or use oral drops.

Clinical Indications & Species Uses

General Indications

Prevention and treatment of fat-soluble vitamin deficiencies
Supportive therapy in conditions with increased oxidative stress

Dog (Canine)

Dietary supplementation for deficiency
Supportive therapy for skin and coat conditions
Adjunct in treatment of certain dermatoses (e.g., seborrhea)
Ophthalmic conditions (vitamin A for retinal health)

Cat (Feline)

Dietary supplementation for deficiency
Supportive therapy for skin and coat conditions
Hepatic lipidosis (vitamin E as antioxidant)

Horse (Equine)

Dietary supplementation for deficiency
Supportive therapy for muscle function (vitamin E/selenium)
Reproductive health (vitamin A and E)

Cattle (Bovine)

Dietary supplementation for deficiency
Prevention of white muscle disease (vitamin E/selenium)
Supportive therapy for fertility and immune function

Small Ruminants (Sheep / Goat)

Dietary supplementation for deficiency
Prevention of white muscle disease (vitamin E/selenium)

Rabbit & Small Mammals

Dietary supplementation for deficiency
Supportive therapy for reproductive health

Avian & Poultry

Dietary supplementation for deficiency
Prevention of vitamin A deficiency (respiratory and ocular signs)
Supportive therapy for immune function

Exotic & Other Species

Reptiles: supplementation for metabolic bone disease (vitamin D3)
Small mammals: general supplementation

Pharmacology & Mechanism of Action

Drug Class: Vitamin Supplement | Pharmacological Group: Fat-Soluble Vitamins

Mechanism of Action: Vitamin A (retinol) is essential for vision (as retinal in rhodopsin), cellular differentiation, immune function, and reproduction. Vitamin D (cholecalciferol or ergocalciferol) is converted to calcitriol, which regulates calcium and phosphorus homeostasis by enhancing intestinal absorption, renal reabsorption, and bone mineralization. Vitamin E (tocopherol) acts as a lipid-soluble antioxidant, protecting cell membranes from oxidative damage by neutralizing free radicals and preventing lipid peroxidation.

Pharmacodynamics: Vitamin A influences gene expression via nuclear retinoic acid receptors, affecting growth and epithelial integrity. Vitamin D binds to vitamin D receptors, modulating calcium-binding proteins and osteoclast activity. Vitamin E donates electrons to free radicals, terminating chain reactions in cell membranes; it also supports immune function and inhibits platelet aggregation.

⚡ Pharmacokinetics Summary

Absorption: All three vitamins are absorbed in the small intestine via chylomicrons, requiring bile salts and pancreatic lipase. Absorption is enhanced by dietary fat and impaired in malabsorptive conditions.

Distribution: Vitamin A is stored primarily in the liver (as retinyl esters) and also in adipose tissue. Vitamin D is stored in adipose tissue and muscle; it circulates bound to vitamin D-binding protein. Vitamin E is distributed to all tissues, especially adipose tissue and liver, and is transported in lipoproteins.

Metabolism: Vitamin A is metabolized in the liver to retinal and retinoic acid, then conjugated and excreted. Vitamin D undergoes hydroxylation in the liver (25-hydroxylation) and kidney (1α-hydroxylation) to form active calcitriol. Vitamin E is metabolized in the liver via CYP450 enzymes to carboxychromanol derivatives.

Excretion: Vitamin A metabolites are excreted in bile and urine. Vitamin D metabolites are excreted primarily in bile, with some in urine. Vitamin E is excreted mainly in bile and feces; minimal urinary excretion.

Half-Life: Vitamin A: 9-15 days in dogs; Vitamin D: 2-3 weeks in dogs; Vitamin E: 2-4 days in dogs (but tissue stores can last weeks).

Bioavailability: Oral bioavailability is variable, dependent on formulation and fat content of diet; generally high when administered with food.

Protein Binding: Vitamin A: bound to retinol-binding protein (RBP) and transthyretin; Vitamin D: bound to vitamin D-binding protein (DBP); Vitamin E: bound to lipoproteins (LDL, HDL).

Available Formulations & Strengths

Oral Tablet Various combinations (e.g., 10,000 IU A, 400 IU D, 100 IU E) (PO)

Oral Liquid Various concentrations (e.g., 50,000 IU A/mL, 5,000 IU D/mL, 100 IU E/mL) (PO)

Injectable Solution Combination products (e.g., 500,000 IU A/mL, 75,000 IU D/mL, 50 IU E/mL) (IM)

Powder Various concentrations for feed supplementation (PO)

Contraindications & Clinical Warnings

Contraindications:

Hypervitaminosis A, D, or E
Known hypersensitivity to any component
Hypercalcemia (for vitamin D)
Severe hepatic disease (for vitamin A, due to storage)
Concurrent use with other vitamin D supplements (risk of toxicity)

Warnings & Clinical Precautions:

Use with caution in pregnant animals; excessive vitamin A can be teratogenic.
Vitamin D toxicity can cause hypercalcemia and soft tissue calcification.
Vitamin E may interfere with vitamin K metabolism in animals on anticoagulant therapy.
In food animals, observe withdrawal times.
Do not exceed recommended dosages; fat-soluble vitamins accumulate in tissues.
Injectable formulations may cause injection-site reactions.

Adverse Effects & Reactions

Common:

Gastrointestinal upset (nausea, vomiting, diarrhea) at high doses
Injection-site pain or swelling

Serious / Severe:

Hypervitaminosis A: bone pain, hepatotoxicity, alopecia, teratogenicity
Hypervitaminosis D: hypercalcemia, anorexia, polyuria, polydipsia, soft tissue calcification
Hypervitaminosis E: impaired blood coagulation, increased bleeding tendency

Rare:

Allergic reactions (urticaria, anaphylaxis)
Hepatotoxicity with chronic high doses of vitamin A

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Mineral oil or orlistat	Reduced absorption of fat-soluble vitamins	Moderate
Corticosteroids	May potentiate vitamin D-induced hypercalcemia	Moderate
Warfarin or other anticoagulants	Vitamin E may enhance anticoagulant effect, increasing bleeding risk	High
Tetracyclines	Vitamin A may increase risk of pseudotumor cerebri	Mild
Cholestyramine	Reduced absorption of fat-soluble vitamins	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Vitamin A: anorexia, weight loss, bone pain, hepatomegaly, alopecia, skin lesions, teratogenicity
Vitamin D: hypercalcemia, vomiting, weakness, polyuria, polydipsia, soft tissue calcification
Vitamin E: relatively low toxicity, but may cause bleeding due to vitamin K antagonism

Emergency Treatment Protocol: Discontinue supplementation immediately. For vitamin A toxicity: supportive care, IV fluids, and monitoring liver function. For vitamin D toxicity: treat hypercalcemia with IV fluids, furosemide, corticosteroids, and calcitonin or bisphosphonates if severe. For vitamin E overdose: discontinue and monitor coagulation; administer vitamin K if bleeding occurs.

Food Animal Withdrawal Times

🥩 Meat: 0 days🥛 Milk: 0 days🥚 Eggs: 0 days

Vitamins are generally considered safe with zero withdrawal times, but always follow label instructions and local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25°C), protect from heat and moisture.

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light; keep container tightly closed. Do not freeze injectable solutions.

Dispensing Status: Over-The-Counter (OTC)

Approval Status: Many vitamin products are approved as dietary supplements or feed additives; some injectable combinations are FDA-approved for veterinary use.

Extra-Label (Off-Label) Use: Vitamins are generally considered low-risk and are often available over-the-counter. Extra-label use in food animals must comply with AMDUCA; however, vitamins are typically exempt from withdrawal requirements if used according to label.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Vitamin A/D/E combinations are commonly used in veterinary practice for supplementation, especially in animals on unbalanced diets, with malabsorption syndromes, or under increased oxidative stress. Vitamin E is often used as an antioxidant in conditions like hepatic lipidosis in cats, and vitamin E/selenium combinations are used to prevent white muscle disease in livestock. Vitamin D is crucial for calcium metabolism, and deficiency can lead to rickets in young animals and osteomalacia in adults. However, toxicity is a real concern, especially with vitamins A and D, due to their long half-lives and storage in tissues. Always calculate doses carefully, especially in small animals, and monitor for signs of hypervitaminosis. In food animals, adhere to label instructions and withdrawal times, though vitamins typically have zero withdrawal. For reptiles, vitamin D3 is essential for calcium metabolism, but excessive supplementation can cause soft tissue calcification. Overall, these vitamins are safe when used appropriately, but they are not benign and should be used with respect for their potential toxicities.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)