Drug Monograph
Full clinical overview, indications, dosage references & safety notes.
Drug class: Mineralocorticoid
Main indication: Hypoadrenocorticism (Addison’s disease)
Available forms1 form · 3 strengths documentedShow all ↓
Oral · solid
Tablet 0.1 mg scoredTablet 0.25 mg UK, named-patientTablet 0.5 mg UK, named-patient
Overview
Fludrocortisone (Florinef®) is a synthetic adrenocortical steroid used primarily as an oral mineralocorticoid replacement in dogs and cats with hypoadrenocorticism (Addison’s disease). It may be used as an oral alternative to injectable desoxycorticosterone pivalate (DOCP), particularly when DOCP is unsuitable.
In addition to its strong mineralocorticoid activity, fludrocortisone also has clinically significant glucocorticoid effects. While this may partially reduce the need for additional glucocorticoid supplementation, many patients still require concurrent prednisolone, especially during stress or illness.
Mechanism of Action (MOA): Fludrocortisone increases sodium reabsorption at the renal distal tubule and enhances potassium and hydrogen ion excretion in the collecting tubule. This promotes sodium retention and enhances potassium and hydrogen ion excretion.
Indications
Fludrocortisone is used in dogs and cats for long-term mineralocorticoid replacement in hypoadrenocorticism.
- Hypoadrenocorticism (Addison’s disease): Used as maintenance therapy to replace deficient mineralocorticoids and restore sodium and potassium balance.
- Alternative to DOCP: Used as an oral alternative to injectable desoxycorticosterone pivalate (DOCP), particularly when DOCP is unsuitable.
- Adjunct glucocorticoid support: May provide partial glucocorticoid activity, but additional supplementation is often required based on clinical response.
- Feline primary hyperaldosteronism: In cats, fludrocortisone has been described both as a treatment for primary hyperaldosteronism and as a diagnostic suppression test; the suppression-test protocol is diagnostic and is separate from hypoadrenocorticism maintenance therapy.
Dosage (Reference)
Dog
In dogs, fludrocortisone is used as long-term maintenance therapy for hypoadrenocorticism. Dose adjustments are based primarily on serum electrolyte concentrations (sodium and potassium) and clinical response.
| Clinical use | Route | Dose | Frequency | Notes |
|---|---|---|---|---|
| Initial therapy (Addison’s disease) | PO | 0.01–0.02 mg/kg/day | q24h, or divided q12h | Starting dose; titrate on serum electrolytes before increasing. |
| Maintenance therapy | PO | 0.02–0.03 mg/kg/day | q24h, or divided q12h | Most dogs require this range after stabilization. |
| Dose adjustment | PO | Adjust by 0.05–0.1 mg increments | every 5 days | One step is half to one 0.1 mg tablet; the tablet is scored. |
Important dosing notes (dogs):
• Monitor serum electrolytes before treatment and every 5–7 days after starting or adjusting dose until stable.
• Once stabilized, recheck electrolytes every 3–6 months; and then every 3–12 months.
• Supplemental glucocorticoid therapy may be required in addition to mineralocorticoid replacement; assess the need and adjust the dose according to the individual patient’s clinical response.
• Owners should keep a supply of prednisolone at home and be told when to give it.
• Always provide extra glucocorticoids during stress or illness (e.g., surgery, hospitalization) — at least twice the basal dose.
• If signs of hyperadrenocorticism (PU/PD) appear → first stop any added glucocorticoids.
• If signs persist → may be due to fludrocortisone’s glucocorticoid effect.
• If electrolytes cannot be normalized → consider switching to DOCP.
• The daily dose needed often rises over the first 6–24 months of therapy, so a dog that was stable can later need more; very few dogs stay controlled on 10 micrograms/kg/day or less.
• Measure absolute sodium and potassium concentrations — not only the ratio — 4–6 hours after the tablet. In dogs on once-daily dosing, also check a pre-dose sample.
• Prednisolone or prednisone may be given at 0.1–0.3 mg/kg/day as adjunct glucocorticoid therapy. Titrate to clinical response; lower maintenance doses, sometimes <0.1 mg/kg/day, may be sufficient when fludrocortisone is given concurrently, particularly in large-breed dogs. Reduce the glucocorticoid dose if polyuria, polydipsia, polyphagia or muscle wasting develops, and increase it if signs of glucocorticoid deficiency, such as vomiting, diarrhoea or lethargy, occur.
• Monitor serum electrolytes before treatment and every 5–7 days after starting or adjusting dose until stable.
• Once stabilized, recheck electrolytes every 3–6 months; and then every 3–12 months.
• Supplemental glucocorticoid therapy may be required in addition to mineralocorticoid replacement; assess the need and adjust the dose according to the individual patient’s clinical response.
• Owners should keep a supply of prednisolone at home and be told when to give it.
• Always provide extra glucocorticoids during stress or illness (e.g., surgery, hospitalization) — at least twice the basal dose.
• If signs of hyperadrenocorticism (PU/PD) appear → first stop any added glucocorticoids.
• If signs persist → may be due to fludrocortisone’s glucocorticoid effect.
• If electrolytes cannot be normalized → consider switching to DOCP.
• The daily dose needed often rises over the first 6–24 months of therapy, so a dog that was stable can later need more; very few dogs stay controlled on 10 micrograms/kg/day or less.
• Measure absolute sodium and potassium concentrations — not only the ratio — 4–6 hours after the tablet. In dogs on once-daily dosing, also check a pre-dose sample.
• Prednisolone or prednisone may be given at 0.1–0.3 mg/kg/day as adjunct glucocorticoid therapy. Titrate to clinical response; lower maintenance doses, sometimes <0.1 mg/kg/day, may be sufficient when fludrocortisone is given concurrently, particularly in large-breed dogs. Reduce the glucocorticoid dose if polyuria, polydipsia, polyphagia or muscle wasting develops, and increase it if signs of glucocorticoid deficiency, such as vomiting, diarrhoea or lethargy, occur.
Cat
In cats, fludrocortisone is used for maintenance treatment of hypoadrenocorticism and may be combined with glucocorticoid supplementation when needed.
| Clinical use | Route | Dose | Frequency | Notes |
|---|---|---|---|---|
| Maintenance therapy (Addison’s disease) | PO | 0.05–0.1 mg/cat | q12h | This regimen is dosed per cat rather than per kilogram. |
| Glucocorticoid supplementation | PO | Prednisolone 2.5–5 mg/cat/day | q24h | Adjust to lowest effective dose. |
| Primary hyperaldosteronism; diagnostic suppression test | PO | 0.05 mg/kg | q12h for 4 days | Used here as a diagnostic suppression test, not as maintenance therapy. Urine aldosterone:creatinine ratio is measured before and after; a shorter variant measures the serum ratio before and after 3 doses. Use as a confirmatory test in cats with an elevated basal urine aldosterone:creatinine ratio; suppression of less than 50% indicates inappropriate aldosterone secretion. |
Important dosing notes (cats):
• The maintenance regimens are calculated per cat rather than per kilogram.
• Evidence for fludrocortisone in feline hypoadrenocorticism is limited — there are very few published reports.
• Prednisolone may be added as needed and should be tapered to the minimum dose that controls clinical signs.
• Measure serum electrolytes before treatment and after any dose change, then every 5–7 days until sodium and potassium normalise; once stable, recheck every 3–6 months.
• As in dogs, additional glucocorticoid is required during stress or acute illness — at least twice the basal dose.
• The maintenance regimens are calculated per cat rather than per kilogram.
• Evidence for fludrocortisone in feline hypoadrenocorticism is limited — there are very few published reports.
• Prednisolone may be added as needed and should be tapered to the minimum dose that controls clinical signs.
• Measure serum electrolytes before treatment and after any dose change, then every 5–7 days until sodium and potassium normalise; once stable, recheck every 3–6 months.
• As in dogs, additional glucocorticoid is required during stress or acute illness — at least twice the basal dose.
Warnings & Precautions
Fludrocortisone therapy requires careful monitoring due to its combined mineralocorticoid and glucocorticoid effects, particularly during long-term use.
- Contraindications: Avoid in patients with known hypersensitivity or systemic fungal infections.
- Cardiac and renal disease: Use cautiously due to sodium and fluid retention, which may worsen hypertension, edema, or cardiac workload.
- Electrolyte imbalance risk: Can cause significant potassium loss and sodium retention; close monitoring is required.
- Immunosuppression: Chronic use increases susceptibility to infections.
- Gastrointestinal risk: Use cautiously in patients with fresh intestinal anastomoses or active or latent peptic ulceration.
- Endocrine and metabolic effects: May contribute to glucose elevation and metabolic alterations associated with corticosteroids.
- Ocular effects: Long-term use may increase risk of cataracts or glaucoma.
- Neuromuscular conditions: Use cautiously in patients with myasthenia gravis or osteoporosis.
- Withdrawal: Discontinuation should be gradual to avoid adrenal suppression.
- Thyroid effects: Thyroid gland atrophy has been reported after chronic glucocorticoid administration.
- Pregnancy and lactation: Safety has not been established in pregnancy or lactation. Corticosteroids are teratogenic in animals and may be excreted in clinically significant quantities in milk; puppies and kittens of treated mothers should receive milk replacer after colostrum. Use only when the benefit to the mother outweighs the risk to the offspring.
- Not for other conditions: Because of its marked sodium-retaining effect, fludrocortisone should not be used for conditions other than mineralocorticoid replacement.
- Intradermal allergy testing: Suppression of intradermal test results may persist for 1–2 weeks after stopping; discontinue at least 2 weeks before testing.
Drug Interactions
The listed interactions have been reported or are theoretical in humans or animals. Concurrent use is not necessarily contraindicated; weigh the potential risks and use additional monitoring when appropriate.
- Amphotericin B: Increased risk of hypokalemia.
- Aspirin: Increased risk of gastrointestinal adverse effects, and salicylate levels may be reduced.
- Calcitriol: Reduced therapeutic effectiveness.
- Cholestyramine: Decreased oral bioavailability of fludrocortisone.
- Other corticosteroids: Increased risk of adverse steroid effects.
- Cosyntropin: May interfere with diagnostic testing.
- Desmopressin: Increased risk of hyponatremia.
- Digoxin: Increased toxicity risk due to hypokalemia.
- Potassium-depleting diuretics: Increased risk of hypokalemia; may counteract sodium-retaining effects.
- Hypoglycemic agents: Reduced efficacy due to increased blood glucose.
- Immunosuppressive drugs: Increased risk of infection.
- NSAIDs: Increased risk of gastrointestinal complications.
- Phenobarbital and rifampin: May reduce drug efficacy.
- Vaccines: Reduced immune response.
- Radioiodine (I-131): Uptake of radioiodine (I-131) by thyroid tissue may be reduced.
- Laboratory tests: Laboratory considerations: may raise serum cholesterol and urine glucose, lower serum potassium, suppress thyroid-stimulating hormone with reduced T3 and T4, and cause false-negative nitroblue tetrazolium results. Fludrocortisone has also suppressed serum aldosterone in healthy cats, and can significantly reduce urine aldosterone concentrations.
Side Effects & Overdose
Side Effects
Adverse effects of fludrocortisone are usually associated with chronic administration, excessive dosing, or its inherent glucocorticoid activity.
- Polyuria and polydipsia: May occur in some animals, from the drug’s glucocorticoid activity.
- Polyphagia: Increased appetite may develop with prolonged use.
- Panting: Seen in some dogs as part of corticosteroid effects.
- Gastrointestinal disturbances: Vomiting or general GI upset may occur.
- Dose relationship: Adverse effects are dose-related and are generally associated with chronic excessive dosing or overly rapid withdrawal.
Overdose
Overdose is primarily characterized by exaggerated mineralocorticoid activity and electrolyte imbalance.
- Hypertension: Due to excessive sodium and fluid retention.
- Edema: Peripheral or generalized fluid accumulation may develop, including cerebral oedema.
- Hypokalemia: Significant potassium loss requiring correction.
- Management: Temporarily discontinue therapy, monitor electrolytes closely, and provide potassium supplementation if needed before restarting at a lower dose.
- Poison-control consultation: For a known or suspected overdose, contact a 24-hour poison control service that provides veterinary-specific advice.
- Chronic overdosing: Long-term overdosing may instead present as hypercortisolism rather than an acute event.
Key Notes
Practical clinical insights for optimal use in dogs and cats:
- Oral therapy advantage: Provides a convenient alternative to injectable mineralocorticoid therapy.
- Variable response: Individual dose requirements vary widely; therapy must be tailored to each patient.
- Long duration of biologic activity: Human data report that biologic activity persists for 18–36 hours despite a plasma half-life of about 3.5 hours.
- Pharmacokinetics: Human data report a peak concentration about 1.7 hours after dosing, a plasma half-life of about 3.5 hours, and biologic activity persisting 18–36 hours.
- Combination therapy: Some patients require concurrent glucocorticoid therapy for adequate control.
- Comparison with DOCP: DOCP may suppress plasma renin activity more effectively than fludrocortisone, though the clinical significance of this difference is not yet established.
- Chronic management: Treatment is typically lifelong in hypoadrenocorticism.
- Client education: Possible long-term overdosing signs include coat changes, abdominal swelling and hair loss. Possible underdosing signs include weakness, depression, reduced appetite, vomiting and diarrhoea; owners should report the underdosing signs promptly.
- Signs of underdosing: Signs that the dose is too low include weakness, depression, loss of appetite, vomiting and diarrhoea — owners should be told to report these promptly.
- Monitoring: Also covers body weight, examination for peripheral and pulmonary oedema, baseline and periodic blood pressure, and signs of glucocorticoid excess.
- Administration with food: May be given with or without food; if the animal vomits on an empty stomach, give with food or a small treat. If vomiting continues, contact the veterinarian.
- Storage: Store tablets at room temperature, 20–25°C, in well-closed containers and away from excessive heat; some formulations require refrigeration, so check the label.
- Compounding: Crushed tablets prepared in suspension have been reported stable for 14 days.
- Reported survival: Similar whether dogs are maintained on fludrocortisone or on injectable DOCP.
- Regulatory status: Use in dogs and cats is extra-label — there is no veterinary-licensed product; the tablets are human-labelled.
