Sildenafil and Itraconazole: Can They Be Taken Together?

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What is sildenafil and itraconazole used for?

Sildenafil is a prescription medicine licensed in the UK to treat erectile dysfunction (ED) in adult men [3]. It belongs to a group of medicines called PDE5 inhibitors, which work by relaxing blood vessels in the penis, allowing increased blood flow when you are sexually aroused. Sildenafil is available in 25mg, 50mg and 100mg tablets, and is usually taken about one hour before sexual activity, with effects lasting up to four hours. The medicine requires sexual stimulation to work and does not increase sexual desire on its own.

Itraconazole is a potent antifungal medicine used to treat a wide range of fungal infections, including nail infections, skin infections, and more serious systemic fungal conditions [12]. It works by stopping the growth of fungi. Itraconazole is broken down in the liver by the same enzyme system (CYP3A4) that processes sildenafil, which is why the two medicines can interact when taken together. Your prescriber needs to know about all medicines you are taking, including antifungals, before prescribing sildenafil.

How do sildenafil and itraconazole interact with each other?

The interaction between sildenafil and itraconazole occurs because itraconazole is a potent inhibitor of an enzyme called CYP3A4 in the liver [3]. This enzyme is responsible for breaking down sildenafil in your body. When itraconazole blocks this enzyme, sildenafil is not cleared from your bloodstream as quickly as usual, leading to higher levels of the medicine staying in your system for longer. This can increase both the effectiveness and the risk of side effects from sildenafil, such as headaches, flushing, dizziness, visual disturbances, and low blood pressure.

Because of this interaction, the standard dose of sildenafil may be too high if you are taking itraconazole at the same time [3]. The British National Formulary advises that the dose of sildenafil should be reduced when used alongside potent CYP3A4 inhibitors like itraconazole. This is not a reason to avoid the combination entirely, but it does mean that careful prescribing and monitoring are essential. Your prescriber will assess your current medicines and adjust the sildenafil dose accordingly to keep you safe while still providing effective treatment for erectile dysfunction.

What does 'potent CYP3A4 inhibitor' mean in plain English?

CYP3A4 is one of the main enzymes in your liver that breaks down many medicines, including sildenafil. A 'potent inhibitor' like itraconazole strongly blocks this enzyme, so medicines that rely on CYP3A4 for breakdown stay in your body much longer and at higher concentrations. Think of it like a drain that has been partially blocked: the water (or medicine) takes much longer to clear away. This is why dose adjustments are needed when these medicines are combined.

What will my prescriber check before prescribing sildenafil and itraconazole together?

Before prescribing sildenafil to someone taking itraconazole, a UK prescriber will carry out a thorough medication review during the online consultation [2]. They will ask about all your current medicines, including prescription drugs, over-the-counter treatments, and herbal supplements. This is because several other medicines can also interact with sildenafil, and the prescriber needs the full picture to make a safe decision. They will check that you are not taking any medicines that are absolutely contraindicated with sildenafil, such as nitrates, nicorandil, riociguat, or other PDE5 inhibitors.

The prescriber will also review your cardiovascular health, blood pressure, and any history of heart problems, stroke, or eye conditions [2]. Because itraconazole increases sildenafil levels, the prescriber will typically recommend starting with a lower dose of sildenafil—often 25mg rather than the standard 50mg starting dose. They may also advise you not to take sildenafil more frequently than recommended and to watch carefully for side effects. If you experience dizziness, severe headache, visual changes, or an erection lasting more than four hours, you should seek medical advice immediately.

Will I need a different dose of sildenafil?

Yes, most people taking itraconazole will be prescribed a lower starting dose of sildenafil to account for the increased drug levels caused by the interaction [3]. A typical starting dose might be 25mg instead of 50mg. Your prescriber will give you clear instructions on the dose that is safe for you, and you should never increase the dose or take it more often than advised without speaking to your prescriber or pharmacist first.

What you need to know

• Sildenafil and itraconazole can be used together, but a lower dose of sildenafil is needed to avoid side effects.
• Itraconazole blocks the enzyme that breaks down sildenafil, causing higher drug levels in your bloodstream.
• Your prescriber will typically start you on 25mg sildenafil instead of 50mg if you are taking itraconazole.
• Always declare all your medicines during the consultation, including antifungals and over-the-counter treatments.
• Seek urgent help if you have an erection lasting over four hours or sudden vision or hearing loss.

Are there any warning signs I should watch for when taking sildenafil and itraconazole?

When taking sildenafil alongside itraconazole, you should be aware of the common side effects of sildenafil, which may be more noticeable or occur more frequently because of the higher drug levels [3]. These include headache, facial flushing, indigestion, nasal congestion, dizziness, and visual disturbances such as a blue tinge to vision or increased sensitivity to light. Most side effects are mild and temporary, but if they are severe or persistent, contact your prescriber or pharmacist for advice.

More serious warning signs require urgent medical attention. If you develop an erection that lasts longer than four hours (priapism), you must go to A&E immediately, as this can cause permanent damage if not treated promptly [3]. Sudden loss of vision in one or both eyes, or sudden decrease or loss of hearing (sometimes with ringing in the ears or dizziness), are rare but serious side effects that need same-day medical assessment. If you experience chest pain during or after sexual activity, stop and seek urgent help, especially if you have a history of heart problems. Do not take any nitrate medicines (such as GTN spray) if you have used sildenafil, as this combination can cause a dangerous drop in blood pressure.

Practical advice for using sildenafil and itraconazole safely together

If you have been prescribed both sildenafil and itraconazole, take each medicine exactly as directed by your prescriber [3]. Do not adjust the dose yourself or take sildenafil more often than recommended. Sildenafil is usually taken about one hour before sexual activity, and you should not take more than one dose in 24 hours. Sexual stimulation is still needed for the medicine to work. Avoid drinking large amounts of alcohol, as this can increase the risk of dizziness and low blood pressure, and may also make erectile dysfunction worse.

Grapefruit and grapefruit juice can also increase sildenafil levels in a similar way to itraconazole, so it is best to avoid grapefruit products while taking sildenafil [3]. Keep your prescriber and pharmacist informed of any new medicines you start, including over-the-counter treatments and herbal remedies like St John's wort, which can reduce the effectiveness of sildenafil. If your itraconazole treatment finishes, let your prescriber know, as they may be able to adjust your sildenafil dose back to a standard level. Always store your medicines safely, out of reach of children, and check the expiry dates.

Can I take sildenafil if I'm on a short course of itraconazole?

Yes, you can take sildenafil during a short course of itraconazole, but the dose of sildenafil will need to be adjusted [3]. Even a short course of itraconazole can significantly affect how your body processes sildenafil, so it is important to declare the antifungal during your consultation. Your prescriber will recommend the safest dose for the duration of your itraconazole treatment and can advise when it may be appropriate to return to a higher dose once the antifungal course is finished.

When to get urgent help

• An erection lasting longer than 4 hours (priapism) – go to A&E immediately
• Sudden loss of vision in one or both eyes – seek same-day medical assessment
• Sudden decrease or loss of hearing, possibly with ringing in the ears or dizziness
• Chest pain during or after sexual activity – stop and seek urgent help; do not take nitrates
• Severe dizziness, fainting, or signs of very low blood pressure

Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.

What other medicines interact with sildenafil in a similar way to itraconazole?

Several other medicines are potent CYP3A4 inhibitors and interact with sildenafil in the same way as itraconazole [3]. These include ketoconazole (another antifungal), certain antibiotics such as clarithromycin and erythromycin, and HIV medicines including ritonavir and cobicistat. Paxlovid, a COVID-19 treatment that contains ritonavir, also falls into this category. If you are taking any of these medicines, your prescriber will adjust your sildenafil dose or may recommend an alternative treatment for erectile dysfunction.

Other interactions to be aware of include alpha-blockers (such as tamsulosin, doxazosin, or alfuzosin), which are often prescribed for prostate problems or high blood pressure [3]. The combination of sildenafil and an alpha-blocker can cause dizziness or a significant drop in blood pressure, so you should be stable on your alpha-blocker before starting sildenafil, and the lowest dose of sildenafil should be used initially. Never take sildenafil with nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, or recreational drugs known as 'poppers' (amyl or alkyl nitrites), as these combinations can cause a dangerous fall in blood pressure. Do not take more than one PDE5 inhibitor at the same time. Your prescriber and pharmacist will check all your current medicines during the consultation to ensure sildenafil is safe for you.

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