No. According to FDA drug labeling and interaction databases, ketoconazole and abemaciclib should not be used together. Ketoconazole is predicted to increase abemaciclib levels in the body by up to 16-fold, which could lead to serious toxicity. If you are taking abemaciclib for cancer and need to treat a fungal infection, you will need to discuss alternative options with your physician or pharmacist.
The documented interaction between abemaciclib and ketoconazole is classified as contraindicated—the highest level of severity, meaning the combination should be avoided.
This interaction is documented in FDA-reviewed drug labeling for abemaciclib (accessed via NLM/NIH RxNorm and FDA drug information sources). The contraindication reflects substantial evidence that combining these drugs creates an unacceptable risk.
A 16-fold increase means that ketoconazole could cause abemaciclib levels in your bloodstream to become 16 times higher than they would be on abemaciclib alone. Abemaciclib is dosed carefully on the basis of the amount that safely reaches the body. When a drug accumulates to much higher levels than intended, the risk of side effects rises sharply.
Your body breaks down most drugs through a set of chemical pathways. One of the most important is an enzyme called CYP3A4, which lives mainly in your liver and intestines. This enzyme is responsible for metabolizing abemaciclib—that is, converting it into inactive forms that your body can eliminate.
Ketoconazole is a strong inhibitor of CYP3A4. When you take ketoconazole, it blocks CYP3A4 from doing its job, which means abemaciclib cannot be broken down efficiently. The drug then builds up in your system to dangerous levels.
Abemaciclib is a cyclin-dependent kinase (CDK) inhibitor—a type of cancer medication that works by interfering with cell division. Abemaciclib is dosed at a level that controls cancer cells while keeping toxicity manageable. This narrow therapeutic window means that even a modest increase in abemaciclib levels can push side effects from tolerable to serious. A 16-fold increase crosses far beyond that boundary.
The mechanism supplied in the source record is CYP3A4 inhibition—a documented, specific cause of this interaction. This is not theory; it is the established reason ketoconazole interferes with abemaciclib metabolism. General pharmacology helps us understand why CYP3A4 inhibitors are problematic with many drugs, but the 16-fold magnitude and the contraindication status apply specifically to this pair and reflect actual clinical and preclinical evidence reviewed by the FDA.
Anyone taking abemaciclib for cancer should be aware of this interaction, especially if they have a history of fungal infections or are at risk for developing one (such as patients with weakened immune systems). However, because the interaction is contraindicated, the question is not who should be careful—it is that all patients on abemaciclib should have an alternative to ketoconazole identified before a fungal infection arises, if possible.
Patients should mention abemaciclib use to any healthcare provider who prescribes antifungal medications. Conversely, anyone already taking ketoconazole should confirm with their oncologist before starting abemaciclib whether ketoconazole can be safely stopped or switched to an alternative.
Suppose a patient is taking abemaciclib for breast cancer and develops a yeast infection. Before prescribing any antifungal, the prescriber should ask about abemaciclib. Learning that the patient takes abemaciclib, the prescriber would avoid ketoconazole and instead consider alternatives like fluconazole or topical antifungal agents (if appropriate for the infection type). This is how the contraindication is managed in practice: by planning ahead and choosing a safer alternative.
Suppose a patient has been taking ketoconazole for a chronic fungal infection and is now being considered for abemaciclib as part of their cancer treatment. Before abemaciclib is started, the clinical team would need to decide whether ketoconazole can be stopped, switched to an alternative antifungal (one that does not strongly inhibit CYP3A4), or managed on a different schedule. Abemaciclib should not be initiated while ketoconazole is on board.
If you are taking or considering abemaciclib and have a fungal infection—or suspect you might be at risk for one—here are questions to bring to your healthcare team:
Do not stop, start, or switch any medication on your own. These decisions require input from your oncologist and pharmacist, who can weigh the benefits and risks in your specific situation.
If you are taking abemaciclib, ketoconazole, or both, review your full medication list at checkdruginteractions.com to identify any documented interactions. Then schedule a conversation with your pharmacist or physician to confirm that your current medications are compatible and to develop a plan for managing any infections that might arise. Your healthcare team is the best resource for personalized advice on whether a medication change is necessary and what alternatives are available.
CDI checks every pair across up to 20 drugs — backed by FDA and NIH data.
Drug interaction data sourced from U.S. FDA drug labeling via openFDA and the U.S. National Library of Medicine (NLM), National Institutes of Health. For informational purposes only. Always consult your pharmacist or physician before making any medication decisions.
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