Ketoconazole

What is this medication for?

• Histoplasmosis (still considered drug of choice by some), other systemic mycoses, hyperadrenocorticism (short-term/palliative), cyclosporine dose-sparing
• Systemic mycoses — controversial, some clinicians avoid entirely

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.

• Most potent CYP450/P-glycoprotein inhibitor of the azole antifungals — highest drug interaction burden of the group; never combine with ivermectin.
• Give with food to improve tolerance in animals prone to stomach/intestinal upset; absorption is acid-dependent so avoid concurrent acid-reducing drugs.

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

• stomach/intestinal (loss of appetite, vomiting, diarrhea) (Most common, more prevalent)
• Reversible lightening of haircoat (Reported)
• ↓ Testosterone/cortisol synthesis (Dose-related, transient)
• Cataracts (Reported)

Worth a phone call to your veterinarian

• Hepatotoxicity (cholangiohepatitis, ↑enzymes) (Idiosyncratic or dose-related)
• Thrombocytopenia (Rare)

⚠️ 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: Hypersensitivity; many consider cats a relative/absolute contraindication
• has or has had: Hepatic disease, low platelet counts; male breeding dogs (testosterone suppression, reversible)

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Ivermectin
  • Cyclosporine
  • Mitotane
  • H2-blockers/antacids/PPIs
  • Digoxin, quinidine, warfarin, cisapride

Storage and handling

Room temperature, protect from light. Needs acidic conditions for solubility — precipitates if compounded alkaline.

Good to know

• Most potent CYP450/P-glycoprotein inhibitor of the azole antifungals — highest drug interaction burden of the group; never combine with ivermectin.
• Considered inferior to mitotane for long-term HAC control but useful for short-term stabilization or palliative therapy before surgery.
• Give with food to improve tolerance in animals prone to stomach/intestinal upset; absorption is acid-dependent so avoid concurrent acid-reducing drugs.