Fludrocortisone Acetate

Mineralocorticoid Corticosteroid

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 0.01-0.02 mg/kg/day q24h (once daily) Duration: Lifelong (maintenance therapy)
Notes: Dose should be adjusted based on serum electrolyte levels (sodium and potassium). Some dogs may require twice-daily dosing. Concurrent glucocorticoid therapy (e.g., prednisone) is usually needed.
Cat PO 0.01-0.02 mg/kg/day q24h (once daily) Duration: Lifelong (maintenance therapy)
Notes: Cats may be more sensitive to side effects; start at lower end of dose range. Monitor electrolytes regularly.
Horse PO Not established Not established Duration: Not established
Notes: Not commonly used in equine practice. If used, extreme caution and monitoring are required.
Cattle PO Not established Not established Duration: Not established
Notes: Not indicated for food animals due to lack of withdrawal information and potential for adverse effects.

Clinical Indications & Species Uses

General Indications
  • Replacement therapy for mineralocorticoid deficiency in hypoadrenocorticism
Dog (Canine)
  • Replacement therapy for primary hypoadrenocorticism (Addison's disease)
  • Replacement therapy for secondary hypoadrenocorticism (with glucocorticoid supplementation)
Cat (Feline)
  • Replacement therapy for primary hypoadrenocorticism (Addison's disease)

Pharmacology & Mechanism of Action

Drug Class: Mineralocorticoid | Pharmacological Group: Corticosteroid

Mechanism of Action: Fludrocortisone acetate is a synthetic corticosteroid with potent mineralocorticoid activity and moderate glucocorticoid activity. It acts primarily on the distal tubules and collecting ducts of the kidney to increase sodium reabsorption and potassium and hydrogen ion excretion. This is achieved by binding to the mineralocorticoid receptor, which then translocates to the nucleus and modulates gene expression, increasing the synthesis of proteins such as the epithelial sodium channel (ENaC) and Na+/K+-ATPase. The net effect is sodium and water retention, expansion of extracellular fluid volume, and increased blood pressure. Its glucocorticoid activity is about 10-15 times that of hydrocortisone, but it is used mainly for its mineralocorticoid effects.

Pharmacodynamics: Fludrocortisone acetate produces dose-dependent increases in sodium retention and potassium excretion. At therapeutic doses, it effectively replaces the mineralocorticoid deficiency in conditions such as hypoadrenocorticism (Addison's disease). It also has some anti-inflammatory and immunosuppressive effects due to its glucocorticoid activity, but these are not the primary therapeutic goals. The onset of action after oral administration is within a few hours, with peak effects on electrolyte balance occurring within 1-2 days. The duration of action is approximately 24 hours, allowing once-daily dosing in most cases.

⚡ Pharmacokinetics Summary

Absorption: Fludrocortisone acetate is well absorbed from the gastrointestinal tract after oral administration. Peak plasma concentrations are reached within 1-2 hours. Food may alter the rate but not the extent of absorption.
Distribution: It is widely distributed throughout the body. It crosses the placenta and is distributed into milk. It is approximately 42% bound to plasma proteins, primarily corticosteroid-binding globulin and albumin.
Metabolism: Fludrocortisone is metabolized in the liver, primarily by reduction and conjugation. The major metabolite is tetrahydrocortisone, which is inactive. Some metabolism may also occur in the kidney.
Excretion: Metabolites are excreted primarily in the urine, with a small amount excreted in bile. The elimination half-life is approximately 3.5 hours in humans, but the biological half-life is longer due to its intracellular effects.
Half-Life: Plasma half-life: ~3.5 hours (human); biological half-life: ~18-36 hours. In dogs, the half-life is approximately 2-4 hours.
Bioavailability: Oral bioavailability is high, estimated at 80-100%.
Protein Binding: Approximately 42% bound to plasma proteins.

Available Formulations & Strengths

Oral Tablet 0.1 mg (PO)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to fludrocortisone or any component of the formulation
  • Systemic fungal infections
  • Congestive heart failure
  • Hypertension
  • Severe renal impairment
  • Hypokalemia (unless corrected)
Warnings & Clinical Precautions:
  • Use with caution in animals with diabetes mellitus, as glucocorticoid activity may increase blood glucose.
  • Use with caution in animals with hepatic disease, as metabolism may be impaired.
  • Use with caution in pregnant or lactating animals; safety not established.
  • Monitor serum electrolytes (sodium, potassium) and blood pressure regularly during therapy.
  • Do not use for anti-inflammatory purposes due to potent mineralocorticoid effects.
  • Abrupt withdrawal may precipitate adrenal crisis in animals with hypoadrenocorticism; taper if discontinuing.

Adverse Effects & Reactions

Common:

  • Polyuria
  • Polydipsia
  • Increased appetite
  • Weight gain
  • Hypokalemia
  • Sodium retention
  • Edema

Serious / Severe:

  • Hypertension
  • Congestive heart failure
  • Muscle weakness
  • Cardiac arrhythmias
  • Adrenal suppression (with prolonged use)

Rare:

  • Hyperglycemia
  • Gastrointestinal ulceration
  • Behavioral changes
  • Cushing's syndrome-like signs (with high doses)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Potassium-depleting diuretics (e.g., furosemide, thiazides) Additive hypokalemia; monitor potassium levels. High
Amphotericin B Increased risk of hypokalemia. Moderate
Insulin or oral hypoglycemic agents May increase blood glucose, requiring dose adjustment of antidiabetic agents. Moderate
NSAIDs Increased risk of gastrointestinal ulceration. Moderate
Phenobarbital or phenytoin Increased hepatic metabolism of fludrocortisone, reducing its efficacy. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Hypertension
  • Hypokalemia
  • Sodium retention
  • Edema
  • Cardiac arrhythmias
  • Muscle weakness
  • Nervousness
  • Hyperglycemia

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Discontinue the drug and monitor electrolytes, blood pressure, and cardiac function. Administer potassium supplementation if hypokalemia is present. In severe cases, consider diuretics for fluid overload. There is no specific antidote.

Food Animal Withdrawal Times

Not approved for use in food animals; no withdrawal times established. Use in food animals is prohibited or requires a very long withdrawal period under extra-label regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F)

Handling & Special Conditions: Protect from moisture. Keep container tightly closed.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use.

Extra-Label (Off-Label) Use: In the US, fludrocortisone is not FDA-approved for veterinary use, but it can be prescribed legally under the Animal Medicinal Drug Use Clarification Act (AMDUCA) for non-food animals. For food animals, extra-label use is prohibited if the drug is not approved for that species and no withdrawal times are established.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Fludrocortisone acetate is the mainstay of mineralocorticoid replacement therapy in dogs and cats with hypoadrenocorticism (Addison's disease). It is typically used in combination with a glucocorticoid such as prednisone. Therapy must be individualized based on serial monitoring of serum electrolytes, blood pressure, and clinical signs. The goal is to maintain normal sodium and potassium levels and to resolve clinical signs such as weakness, lethargy, and gastrointestinal disturbances. Overdosing can lead to hypertension and hypokalemia, while underdosing may result in hyperkalemia and hyponatremia. Owners should be educated on the importance of consistent dosing and regular veterinary check-ups. In emergency situations, parenteral fluids and glucocorticoids are used for acute adrenal crisis, and fludrocortisone is started once the animal is stabilized.

References & Literature

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