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    HomeMedication GuideDrug InteractionsKetoconazole + Sildenafil
    Major interaction

    Does Ketoconazole Interact With Sildenafil?

    7 DRUG INTERACTIONS Sildenafil can potentiate the hypotensive effects of nitrates, alpha blockers, and anti-hypertensives ( 4.1 , 5.5 , 7.1 , 7.2 , 7.3 , 12.2 ) With concomitant use of alpha blockers, initiate sildenafil at 25 mg dose ( 2.3 ) CYP3A4 inhibitors (e.g., ritonavir, ketoconazole, itraconazole, erythromycin): Increase sildenafil exposure ( 2.4 , 7.4 , 12.3 ) Ritonavir: Do not exceed a maximum single dose of 25 mg in a 48 hour period ( 2.4 , 5.6 ) Erythromycin or strong CYP3A4 inhib…

    Reviewed by the OmniRx Health clinical team•Last reviewed Jul 4, 2026

    Severity: Major

    Severity basis: drug interactions section (keywords: contraindicated). Combining Ketoconazole (Azole antifungal (strong CYP3A4 inhibitor)) and Sildenafil (PDE5 inhibitor) is classified as a major interaction.

    What to Do

    The label advises avoiding this combination or using it only under close medical supervision. Talk to your prescriber or pharmacist before combining them.

    How This Interaction Works

    Interactions like this one can happen when two medicines have overlapping effects, or when one changes how the other is absorbed, broken down, or cleared from the body. Ketoconazole is a azole antifungal (strong cyp3a4 inhibitor) and Sildenafil is a pde5 inhibitor; together they are documented as a major interaction. How much this matters depends on your dose, your other medications, and your overall health.

    If You Take Both Medications

    If you have been prescribed both Ketoconazole and Sildenafil, do not start, stop, or change either medication on your own — some medicines are unsafe to stop suddenly. Tell your prescriber and pharmacist that you take both so they can decide whether the combination is right for you, adjust the dose, monitor you more closely, or suggest an alternative.

    From the FDA Label

    7 DRUG INTERACTIONS Sildenafil can potentiate the hypotensive effects of nitrates, alpha blockers, and anti-hypertensives ( 4.1 , 5.5 , 7.1 , 7.2 , 7.3 , 12.2 ) With concomitant use of alpha blockers, initiate sildenafil at 25 mg dose ( 2.3 ) CYP3A4 inhibitors (e.g., ritonavir, ketoconazole, itraconazole, erythromycin): Increase sildenafil exposure ( 2.4 , 7.4 , 12.3 ) Ritonavir: Do not exceed a maximum single dose of 25 mg in a 48 hour period ( 2.4 , 5.6 ) Erythromycin or strong CYP3A4 inhib…

    Source: FDA structured product labeling (set_id 00ee09dd-2de0-4dc4-85f6-b51ed6eabd5b).

    Ketoconazole

    Azole antifungal (strong CYP3A4 inhibitor)

    Brands: Nizoral

    View Ketoconazole safety profile

    Sildenafil

    PDE5 inhibitor

    Brands: Viagra, Revatio

    View Sildenafil safety profile

    Check these against your full medication list in our free Interaction Checker

    Frequently Asked Questions

    Can you take Ketoconazole and Sildenafil together?

    Ketoconazole and Sildenafil have a documented major interaction. The label advises avoiding this combination or using it only under close medical supervision. Talk to your prescriber or pharmacist before combining them.

    How serious is the Ketoconazole and Sildenafil interaction?

    It is classified as a major interaction, based on the FDA label's drug interactions section (keywords: contraindicated). A major interaction can cause serious harm and often calls for a change in therapy or close monitoring.

    What should I do if I'm taking both Ketoconazole and Sildenafil?

    If you have been prescribed both Ketoconazole and Sildenafil, do not start, stop, or change either medication on your own — some medicines are unsafe to stop suddenly. Tell your prescriber and pharmacist that you take both so they can decide whether the combination is right for you, adjust the dose, monitor you more closely, or suggest an alternative.

    This information is educational — not medical advice.

    This page is provided for general educational purposes and summarizes publicly available data from sources such as the U.S. Food & Drug Administration. It is not a substitute for the judgment of a licensed clinician and should not be used to start, stop, or change any medication. It may be incomplete or out of date, and individual circumstances vary. Always talk with your prescriber or pharmacist about your specific medications and health conditions. If you think you may have a medical emergency, call 911.

    Questions About Your Medications?

    A licensed OmniRx provider can review your full medication list and help you understand what's safe for you — no office visit required.

    Other Ketoconazole Interactions

    Sources & References

    Learn more about where our data comes from and how we write and review medical content.