Iodide (Potassium-, Sodium-)

Overview

Potassium iodide and sodium iodide are iodide salts used in dogs and cats primarily for the treatment of sporotrichosis. Although both formulations have been used clinically, potassium iodide is the most commonly administered oral preparation, while azole antifungal agents are generally preferred because they are associated with fewer adverse effects.

Use in cats remains controversial because they appear to be more susceptible to iodide toxicity and other adverse effects. Careful dose escalation and close monitoring are recommended throughout treatment.

Mechanism of Action (MOA): The exact mechanism by which iodides exert their antifungal effects has not been established. Their therapeutic activity is thought to be related to modulation of the granulomatous inflammatory response rather than direct antimicrobial activity, as iodides have little, if any, in vitro antimicrobial effect.

Indications

Potassium iodide and sodium iodide are used in dogs and cats primarily for the treatment of sporotrichosis. In cats, azole antifungal agents are generally preferred because of the greater risk of adverse effects associated with iodide therapy.

• Sporotrichosis: Used as an extra-label treatment in dogs and cats, either alone or in combination with antifungal therapy, depending on the clinical case.
• Fungal granulomatous disease: Has been used as an adjunctive treatment for zygomycosis, conidiobolomycosis and fungal granuloma, although its efficacy in animals has not been established.
• Radiation emergency: Used to protect the thyroid gland from radiation injury after accidental exposure to radiation.

Dosage (Reference)

Dog

Potassium iodide is used as an extra-label treatment for sporotrichosis in dogs. Administration with food is recommended to improve gastrointestinal tolerance.

Cat

Azole antifungal agents are generally recommended for feline sporotrichosis. When potassium iodide is used as a lower-cost alternative, treatment should begin at a low dose and be gradually increased while monitoring for adverse effects.

Warnings & Precautions

Potassium and sodium iodide should be used cautiously in dogs and cats because adverse effects may occur during treatment, particularly in cats, which appear to be more susceptible to iodide toxicity. Careful patient selection and close monitoring are recommended throughout therapy.

• Hypersensitivity: Contraindicated in animals with known hypersensitivity to iodides.
• Hyperthyroidism: Do not administer to animals with hyperthyroidism.
• Renal disease or dehydration: Avoid use in animals with renal failure or severe dehydration.
• Use in cats: Cats are more prone to developing adverse effects and iodide toxicity; use cautiously and monitor closely during treatment.
• Young animals: May be more susceptible to iodism than adults.
• Pregnancy and lactation: Avoid use during pregnancy or lactation. Iodides cross the placenta and are excreted in milk, with the potential to alter neonatal thyroid function; if an iodide is required in a nursing dam, switch to milk replacer.
• Patient acceptance: Oral iodide solutions have an unpleasant metallic taste that may reduce treatment compliance. Administration with food or high-fat foods may improve palatability.
• Parenteral use: Do not inject iodide intramuscularly, and do not give potassium iodide intravenously.

Drug Interactions

Clinically relevant drug interactions with potassium iodide are primarily related to alterations in potassium homeostasis or thyroid function. When concurrent administration is necessary, appropriate monitoring is recommended.

• ACE inhibitors (e.g., enalapril): Concurrent use with potassium iodide may increase the risk of hyperkalemia.
• Angiotensin receptor blockers (ARBs; e.g., telmisartan): May increase the risk of hyperkalemia when administered with potassium iodide.
• Potassium-sparing diuretics (e.g., spironolactone, triamterene): Concurrent administration may increase the risk of hyperkalemia.
• Potassium supplements: May further increase serum potassium concentrations and the risk of hyperkalemia.
• Antithyroid medications (e.g., methimazole, carbimazole): Iodides may decrease the efficacy of antithyroid drugs.
• Thyroid supplements (e.g., levothyroxine): Iodides may enhance the effects of thyroid replacement therapy.

Side Effects & Overdose

Side Effects

Adverse effects are generally dose-related and are more likely to occur during prolonged treatment or dose escalation. Cats appear to be more susceptible to iodide toxicity than dogs and should be monitored closely throughout therapy.

• Gastrointestinal effects: Vomiting, inappetence, and nausea are the most commonly reported adverse effects. Administering the drug with food or a high-fat meal may improve tolerability.
• Iodism (iodide toxicity): Long-term treatment or excessive doses may result in iodism, characterized by vomiting, inappetence, depression, lethargy, muscle twitching, hypothermia, and cardiovascular failure.
• Hepatic effects (cats): Increased liver enzyme activity and clinical signs of hepatotoxicity have been reported in some treated cats.
• Cardiomyopathy (cats): Potassium iodide administration has been associated with cardiomyopathy in cats.
• Poor palatability: The unpleasant taste of oral iodide solutions may reduce voluntary acceptance. Sodium iodide may be better tolerated than potassium iodide in cats, and compounded capsules may improve administration in small dogs and cats.

Overdose

Overdose or excessive iodine exposure may result in iodism, with clinical severity depending on the amount ingested and duration of exposure.

• Clinical signs: Excessive tearing, vomiting, anorexia, diarrhea, nasal discharge, muscle twitching, cardiomyopathy, scaly haircoat (dandruff), hyperthermia, coughing, inappetence, and decreased milk production and weight gain may occur.
• Potassium-containing formulations: Refer to potassium overdose recommendations when managing overdoses associated with potassium iodide.
• Management: Animals with suspected overdose should receive prompt veterinary evaluation and appropriate supportive care.

Key Notes

Practical clinical points to optimize the use of potassium and sodium iodide in dogs and cats:

• Treatment response: Clinical response should be monitored throughout therapy, with dose adjustments based on efficacy and patient tolerance.
• Monitoring: Assess liver enzymes and thyroid function.
• Capsule formulations: Compounded capsules or commercially available potassium iodide tablets may be useful for small dogs and cats that cannot tolerate oral solutions.
• Choice of iodide salt: Cats may accept sodium iodide better than potassium iodide when oral liquid formulations are used.
• Solution appearance: Discard oral iodide solutions if they develop a brownish-yellow discoloration, as this indicates oxidation and loss of product stability.