Ascorbic Acid

Vitamin Water-soluble vitamin (antioxidant)

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 10-50 mg/kg q12h Duration: Variable; often 2-4 weeks or as needed
Notes: For copper hepatopathy, doses up to 100 mg/kg/day have been used. Monitor for oxalate urolithiasis.
Cat PO 10-30 mg/kg q12h Duration: Variable
Notes: Use with caution in cats with a history of calcium oxalate uroliths.
Horse PO 10-20 g per horse (approximately 20-40 mg/kg) q24h Duration: Variable
Notes: For EMND, higher doses (up to 50 mg/kg) may be used. Oral absorption is limited; IV administration may be more effective.
Cattle SC or IM 2-5 g per animal q24h Duration: 3-5 days
Notes: Used as supportive therapy; not a substitute for specific treatment.
Small Ruminants PO or SC 1-3 g per animal q24h Duration: 3-5 days
Notes: Limited data; use based on clinical judgment.
Rabbit PO 10-50 mg/kg q24h Duration: Variable
Notes: Not routinely required; may be used as an antioxidant.
Bird/Poultry PO (in water) 100-500 mg/L of drinking water q24h Duration: 3-5 days
Notes: Use fresh solution daily; ascorbic acid is unstable in water.
Guinea Pig PO 10-30 mg/kg q24h Duration: Continuous (dietary requirement)
Notes: Deficiency leads to scurvy; ensure adequate dietary intake.

Clinical Indications & Species Uses

General Indications
  • Treatment and prevention of vitamin C deficiency (scurvy) in species requiring dietary intake
  • Antioxidant supplementation in various diseases
Dog (Canine)
  • Adjunct in the treatment of copper-associated hepatopathy (e.g., Bedlington Terriers)
  • Supportive therapy for immune-mediated diseases
  • Antioxidant support in cancer patients
  • Wound healing support
  • Urinary acidification (though efficacy is debated)
Cat (Feline)
  • Supportive therapy for feline infectious peritonitis (FIP) (limited evidence)
  • Antioxidant support in chronic kidney disease
  • Wound healing support
Horse (Equine)
  • Supportive therapy for exercise-induced oxidative stress
  • Adjunct in the treatment of equine motor neuron disease (EMND)
  • Wound healing support
Cattle (Bovine)
  • Supportive therapy for stress (e.g., transport, weaning)
  • Adjunct in the treatment of mastitis (as an antioxidant)
  • Supportive therapy for respiratory disease
Small Ruminants (Sheep / Goat)
  • Supportive therapy for stress
  • Antioxidant support in pregnancy toxemia
Avian & Poultry
  • Prevention and treatment of scurvy in species that require dietary vitamin C (e.g., some passerines)
  • Antioxidant support during heat stress
Exotic & Other Species
  • Guinea pigs: prevention and treatment of scurvy (essential dietary requirement)
  • Primates: prevention and treatment of scurvy
  • Fish: prevention of deficiency (e.g., in salmonids)

Pharmacology & Mechanism of Action

Drug Class: Vitamin | Pharmacological Group: Water-soluble vitamin (antioxidant)

Mechanism of Action: Ascorbic acid (vitamin C) is a water-soluble antioxidant that acts as a cofactor in numerous enzymatic reactions, including collagen synthesis (hydroxylation of proline and lysine), carnitine synthesis, neurotransmitter synthesis (dopamine to norepinephrine), and steroidogenesis. It also regenerates other antioxidants (e.g., vitamin E) and modulates immune function by enhancing neutrophil activity and lymphocyte proliferation. In veterinary medicine, it is used primarily for its antioxidant properties and to correct deficiency states.

Pharmacodynamics: Ascorbic acid scavenges reactive oxygen species (ROS) and reactive nitrogen species, protecting cells from oxidative damage. It enhances iron absorption by reducing ferric to ferrous iron. It is essential for the maintenance of connective tissue integrity, wound healing, and bone formation. In some species (e.g., primates, guinea pigs, and some fish), it is a vitamin because they lack L-gulonolactone oxidase, the enzyme required for its synthesis. In most domestic animals, it is synthesized in the liver, so deficiency is rare except under stress or certain diseases.

⚑ Pharmacokinetics Summary

Absorption: Absorbed readily from the gastrointestinal tract via an active sodium-dependent transport process at low doses and passive diffusion at high doses. Bioavailability is dose-dependent; high doses may reduce fractional absorption.
Distribution: Widely distributed throughout body tissues, with highest concentrations in the adrenal glands, pituitary, and leukocytes. It crosses the placenta and is distributed into milk. Protein binding is minimal (about 25% in humans).
Metabolism: Metabolized primarily in the liver to inactive metabolites (e.g., oxalate, ascorbate-2-sulfate). In dogs and cats, the liver can synthesize ascorbic acid from glucose, but under stress or disease, endogenous synthesis may be insufficient.
Excretion: Excreted primarily in urine as unchanged ascorbic acid and metabolites. Renal excretion increases with high plasma concentrations. In ruminants, some metabolism occurs in the rumen.
Half-Life: Dogs: approximately 2-4 hours; Cats: approximately 2-3 hours; Horses: approximately 1-2 hours; Humans: 10-20 days (but not relevant).
Bioavailability: Oral bioavailability is dose-dependent; high doses may have reduced absorption. In dogs, oral bioavailability is approximately 70-90% at low doses.
Protein Binding: Approximately 25% (minimal)

Available Formulations & Strengths

Oral Tablet 25 mg, 50 mg, 100 mg, 250 mg, 500 mg, 1000 mg (PO)
Oral Capsule 250 mg, 500 mg, 1000 mg (PO)
Oral Powder Various (e.g., 100 g, 500 g) (PO)
Injectable Solution 100 mg/mL, 250 mg/mL, 500 mg/mL (IV, IM, SC)
Oral Liquid 100 mg/mL (PO)

Contraindications & Clinical Warnings

Contraindications:
  • Known hypersensitivity to ascorbic acid
  • Patients with a history of calcium oxalate urolithiasis (high doses may increase oxalate excretion)
  • Patients with glucose-6-phosphate dehydrogenase deficiency (rare in animals)
  • Do not administer intravenously to patients with renal insufficiency (may cause hyperoxalemia)
Warnings & Clinical Precautions:
  • Use with caution in patients with renal disease, as high doses may increase oxalate load and risk of calcium oxalate crystal formation.
  • High doses may interfere with urine glucose testing (false negatives) and fecal occult blood tests.
  • In animals that synthesize vitamin C (e.g., dogs, cats), supplementation is generally unnecessary and may be harmful in excessive doses.
  • Prolonged high-dose therapy may cause hemolysis in patients with glucose-6-phosphate dehydrogenase deficiency (rare in animals).
  • Injectable solutions may cause tissue irritation if given IM or SC; administer slowly IV when possible.
  • In food animals, observe withdrawal times; ascorbic acid is generally considered low risk, but regulatory guidelines should be followed.

Adverse Effects & Reactions

Common:

  • Gastrointestinal upset (diarrhea, nausea) at high oral doses
  • Tissue irritation at injection site

Serious / Severe:

  • Calcium oxalate urolithiasis (with chronic high doses)
  • Oxalate nephropathy (rare, with high IV doses)
  • Hemolysis in G6PD-deficient patients

Rare:

  • Allergic reactions
  • Hyperoxalemia
  • Interference with laboratory tests

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Iron supplements Ascorbic acid enhances iron absorption; may increase risk of iron toxicity if given concurrently. Moderate
Corticosteroids Corticosteroids may increase ascorbic acid requirements and decrease tissue levels. Mild
Warfarin and other anticoagulants High doses of ascorbic acid may antagonize the anticoagulant effect of warfarin. Moderate
Fluphenazine and other phenothiazines Ascorbic acid may decrease the therapeutic effect of phenothiazines. Mild
Aluminum-containing antacids Ascorbic acid may increase aluminum absorption, potentially increasing toxicity risk. Mild

Overdose & Toxicity Management

Signs of Toxicity:

  • Gastrointestinal upset (diarrhea, abdominal pain)
  • Polyuria and polydipsia (due to osmotic diuresis)
  • Calcium oxalate crystalluria and urolithiasis
  • Hemolysis (in G6PD-deficient patients)

Emergency Treatment Protocol: Discontinue ascorbic acid. Provide supportive care, including fluid therapy to promote diuresis and reduce oxalate concentration. Monitor renal function and urine sediment for crystals. In severe cases, consider alkalinization of urine to increase oxalate solubility. There is no specific antidote.

Food Animal Withdrawal Times

πŸ₯© Meat: 0 daysπŸ₯› Milk: 0 daysπŸ₯š Eggs: 0 days

Ascorbic acid is generally considered a low-risk substance in food animals. However, for extra-label use, follow regulatory guidelines and consult the FARAD database for specific withdrawal times. In the US, ascorbic acid is not approved for use in food animals, but it is often used off-label; withdrawal times may be set by the veterinarian based on risk assessment.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25Β°C, excursions permitted to 15-30Β°C). Protect from moisture.

Light Sensitivity: Light-sensitive β€” protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep container tightly closed. Injectable solutions should be stored at room temperature and protected from light; do not freeze.

Dispensing Status: Over-The-Counter (OTC)

Approval Status: Ascorbic acid is generally recognized as safe (GRAS) for use in human foods and is available as a dietary supplement. In veterinary medicine, there are FDA-approved products for certain species (e.g., injectable for cattle), but many uses are extra-label.

Extra-Label (Off-Label) Use: Ascorbic acid is a non-prescription vitamin in most countries. In veterinary medicine, it is often used extra-label (e.g., in food animals) under the Animal Medicinal Drug Use Clarification Act (AMDUCA) in the US. Extra-label use requires a valid veterinarian-client-patient relationship and must follow label directions for approved drugs when available. For food animals, withdrawal times must be established by the veterinarian.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Ascorbic acid is a water-soluble vitamin with antioxidant properties. In veterinary practice, it is most commonly used as a supportive therapy in conditions associated with oxidative stress, such as sepsis, trauma, and chronic inflammatory diseases. It is essential in species that cannot synthesize it (e.g., guinea pigs, primates, some fish). In dogs and cats, endogenous synthesis usually meets requirements, but supplementation may be beneficial in certain diseases (e.g., copper hepatopathy). Doses should be tailored to the species and condition. High doses can cause gastrointestinal upset and increase the risk of calcium oxalate urolithiasis, so caution is advised in patients with a history of urinary stones. Injectable forms should be used with care due to tissue irritation. Always consider the potential for drug interactions and monitor patients for adverse effects.

References & Literature

  • πŸ“š Plumb's Veterinary Drug Handbook
  • πŸ“š Papich Veterinary Pharmacology and Therapeutics
  • πŸ“š Compendium of Veterinary Products (CVP)