What Is Ketoconazole (Nizoral®)?

Reviewed by: HU Medical Review Board | Last reviewed: September 2022 | Last updated: October 2022

Ketoconazole (Nizoral®) is an antifungal medicine used to treat certain fungal infections. At high doses, it is also considered an anti-androgen. This means it reduces androgen hormones, which prostate cancers often use to grow. Ketoconazole has been used to treat certain forms of prostate cancer for many years.1,2

The US Food and Drug Administration (FDA) has not yet approved ketoconazole to treat prostate cancer. It is not usually the first treatment used for prostate cancer, but it typically costs less and may be safer for some people than other treatments. Serious side effects are possible. Talk to your doctor about the risks and benefits of ketoconazole.1,2

What are the ingredients in ketoconazole?

The active ingredient in ketoconazole is ketoconazole.1,2

How does ketoconazole work?

Prostate cancers often use androgens to grow. Androgens are a type of hormone. Everybody has androgen hormones, and they serve various purposes in the body. Reducing androgen levels can slow the growth of some prostate cancers. This is why drugs that help lower these levels are an option to treat certain forms of prostate cancer.2,3

Ketoconazole blocks an enzyme called CYP17A1. CYP17A1 is part of a process that converts cholesterol into other hormones. This process is how the body makes glucocorticoids (such as cortisol) and androgens (such as testosterone).3

Blocking CYP17A1 can lower the level of androgens in the body. This can slow or stop the progression of prostate cancer. Ketoconazole is most often used:2,3

What are the possible side effects?

Ketoconazole is taken at a high dose to treat prostate cancer. The safety of higher doses of ketoconazole is not well-studied. But the most common side effects of lower doses of ketoconazole include:1

  • Nausea
  • Headache
  • Diarrhea
  • Stomach pain
  • Abnormal liver function

Ketoconazole has a boxed warning, the strictest warning from the FDA. It has this warning in part because it can cause serious liver problems. In rare cases, these can be life-threatening. Talk to your doctor if you notice symptoms of liver toxicity, including:1

  • Loss of appetite
  • Weight loss
  • Nausea or vomiting
  • Feeling tired
  • Dark urine or light-colored stool
  • Stomach pain
  • Yellowing of your skin or the whites of your eyes
  • Fever or rash

Ketoconazole also has a boxed warning because it can change your heart’s electrical activity. This is called QT prolongation. It can cause irregular heartbeats that may be life-threatening. QT prolongation is most common when ketoconazole is combined with certain other drugs. Talk to your doctor if you notice symptoms of QT prolongation, including:1

  • Feeling lightheaded
  • Dizziness
  • Fainting
  • Fast or irregular heartbeat

These are not all the possible side effects of ketoconazole. Talk to your doctor about what to expect when taking ketoconazole. Call your doctor if you have any changes that concern you when taking ketoconazole.

Other things to know

Take ketoconazole as your doctor prescribes. It is taken as an oral tablet and often combined with a steroid. Your doctor may monitor your heart and liver function while you are taking ketoconazole.3

Taking high doses of ketoconazole can reduce your levels of other steroids, especially cortisol. This is called adrenal insufficiency. It happens because ketoconazole blocks enzymes that make cortisol. Your doctor may recommend that you take a steroid to prevent adrenal insufficiency. Talk to your doctor if you notice symptoms of adrenal insufficiency, including:1

  • Tiredness
  • Weakness
  • Dizziness
  • Nausea and vomiting

Before beginning treatment with ketoconazole, tell your doctor about your full health history. Certain other health conditions and medicines make ketoconazole less safe to take. Tell your doctor about:1,2

  • Other health conditions, especially liver problems and adrenal insufficiency
  • Personal or family history of heart problems
  • All other medicines you take, including vitamins, supplements, and over-the-counter drugs
  • Any allergies you have

For more information, read the full prescribing information.

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