Spironolactone

What is this medication for?

• Adjunct for CHF (valvular disease) not controlled by furosemide+ACE inhibitor alone, ascites
• CHF adjunct, hyperaldosteronism adjunct

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

• Should never be substituted for furosemide in CHF — it's a weak diuretic on its own; its role is as an aldosterone-blocking adjunct, not a primary diuretic.
• Give with food to significantly improve oral bioavailability in dogs.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• Hyperkalemia, hyponatremia, dehydration (Possible, generally mild/reversible in dogs)
• stomach/intestinal distress, CNS effects (low energy/tiredness, wobbliness/unsteadiness) (Occasional)
• Prostatic atrophy (Reported)

Worth a phone call to your veterinarian

• Severe facial dermatitis (~1/3 of treated Maine Coon cats in one study)

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Hyperkalemia, Addison's disease, anuria, acute renal failure/significant renal impairment; dehydration
• has or has had: Hepatic disease (though used for ascites); gastric ulcer/stomach/intestinal disease risk

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • ACE inhibitors (e.g., enalapril)
  • Digoxin
  • Potassium supplements/other potassium-sparing diuretics
  • NSAIDs, trimethoprim
  • Mitotane
  • Salicylates

Storage and handling

Room temperature, protect from light. Insoluble in water — compounded suspensions require ethanol pre-mixing; stable 90–160 days once properly prepared.

Good to know

• Should never be substituted for furosemide in CHF — it's a weak diuretic on its own; its role is as an aldosterone-blocking adjunct, not a primary diuretic.
• In cats, weigh the real risk of severe facial dermatitis against uncertain efficacy benefit — many clinicians avoid it in cats for this reason.
• Give with food to significantly improve oral bioavailability in dogs.