Vardenafil and Erythromycin: Can They Be Taken Together?

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Vardenafil and Erythromycin: Understanding the Interaction

Published: 30 October 2026

Vardenafil and erythromycin should not be taken together without careful medical supervision, as erythromycin significantly increases vardenafil levels in the blood and raises the risk of side effects. Erythromycin is a macrolide antibiotic commonly prescribed for chest infections, skin infections, and other bacterial conditions, while vardenafil (generic Levitra) is a PDE5 inhibitor used to treat erectile dysfunction. This page explains how these medicines interact, what your prescriber will check, and what practical steps you can take to stay safe.

What Is Vardenafil and How Does It Work?

Vardenafil is a prescription medicine licensed in the UK for the treatment of erectile dysfunction (ED) in adult men [5]. It belongs to a group of medicines called PDE5 inhibitors, which work by relaxing the blood vessels in the penis, allowing increased blood flow when you are sexually aroused. Vardenafil does not cause an erection on its own—sexual stimulation is still needed for it to work [5].

The usual starting dose is 10 mg, taken about 25 to 60 minutes before sexual activity, and the dose can be adjusted by your prescriber to 5 mg or 20 mg depending on how well it works and whether you experience side effects [5]. You should not take vardenafil more than once in 24 hours. Common side effects include headache, flushing, nasal congestion, and indigestion, which are usually mild and temporary [5].

Vardenafil is broken down in the body by liver enzymes, particularly one called CYP3A4. Medicines that interfere with this enzyme can change how much vardenafil stays in your bloodstream, which is why certain drug interactions—including with erythromycin—are clinically important and must be checked by your prescriber [5].

What Is Erythromycin and When Is It Prescribed?

Erythromycin is a macrolide antibiotic used to treat a wide range of bacterial infections, including chest infections (such as pneumonia and bronchitis), skin and soft-tissue infections, acne, and infections in people who are allergic to penicillin. It works by stopping bacteria from making the proteins they need to grow and multiply, helping your immune system to clear the infection.

Erythromycin is available in several forms—tablets, capsules, liquid suspension, and topical preparations—and is usually taken two to four times a day, depending on the infection being treated. Common side effects include nausea, vomiting, diarrhoea, and abdominal discomfort. Like vardenafil, erythromycin is processed by liver enzymes, but it also acts as a potent inhibitor of the CYP3A4 enzyme.

This means that when erythromycin is taken alongside other medicines that rely on CYP3A4 for breakdown—such as vardenafil—it can slow down their elimination from the body, leading to higher blood levels and an increased risk of side effects. This is the mechanism behind the interaction between vardenafil and erythromycin, and it is the reason prescribers must carefully assess whether the combination is appropriate for you.

Other Macrolide Antibiotics

Clarithromycin is another macrolide antibiotic that also strongly inhibits CYP3A4 and has a similar interaction profile to erythromycin. Azithromycin, by contrast, has a much weaker effect on this enzyme and is generally considered safer to use with vardenafil, though your prescriber will still review your individual circumstances. If you are prescribed a macrolide antibiotic and are taking or considering vardenafil, always inform your doctor or pharmacist so they can choose the most appropriate option for you.

How Do Vardenafil and Erythromycin Interact?

The interaction between vardenafil and erythromycin occurs because erythromycin is a potent inhibitor of the CYP3A4 enzyme in the liver, which is responsible for breaking down vardenafil [5]. When erythromycin blocks this enzyme, vardenafil is cleared from the body more slowly, leading to higher blood levels and a longer duration of action. This increases the risk of side effects such as headache, flushing, dizziness, visual disturbances, and—more seriously—a dangerous drop in blood pressure.

According to the British National Formulary, vardenafil is contraindicated (must not be used) with potent CYP3A4 inhibitors, including erythromycin and clarithromycin [5]. This is a precautionary measure to prevent potentially serious adverse effects. If you are already taking erythromycin and develop erectile dysfunction, or if you are prescribed erythromycin while taking vardenafil, your prescriber will need to review your treatment and consider alternative options.

It is important to understand that this interaction is not simply theoretical—it is based on known pharmacokinetic data and clinical guidance. The combination should be avoided unless your prescriber has specifically assessed your individual situation and decided that the benefits outweigh the risks, which is rare. Never start, stop, or change the dose of either medicine without consulting your doctor or pharmacist first.

What Your Prescriber Will Check Before Prescribing Vardenafil

Before prescribing vardenafil, your doctor or pharmacist will take a detailed medical history and review all your current medicines, including prescription drugs, over-the-counter treatments, and herbal supplements [2]. They will specifically ask about antibiotics, antifungals, HIV medicines, and other drugs that can interact with vardenafil. If you are taking erythromycin or clarithromycin, vardenafil will not normally be prescribed [5].

Your prescriber will also check for conditions that make PDE5 inhibitors unsuitable, such as recent heart attack or stroke, unstable angina, severe heart failure, very low blood pressure, or a history of sudden vision loss (non-arteritic anterior ischaemic optic neuropathy, or NAION) [5]. They will ask about nitrate medicines (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, and recreational drugs called 'poppers', as these must never be taken with vardenafil due to the risk of a life-threatening drop in blood pressure [5].

If you are taking alpha-blockers for prostate symptoms or high blood pressure (such as tamsulosin or doxazosin), your prescriber will ensure you are stable on that treatment and may start you on a lower dose of vardenafil to reduce the risk of dizziness or fainting [5]. The consultation is designed to ensure that vardenafil is safe and appropriate for you, and that any potential interactions are identified and managed before you start treatment.

Online Consultations at Cured Pharmacy

At Cured Pharmacy, all requests for prescription ED treatments are reviewed by a UK-registered prescriber as part of a confidential online consultation. You will be asked to provide details of your medical history, current medicines, and any allergies. This information is carefully checked to ensure that the treatment is safe for you. If there are any concerns—such as a potential interaction with erythromycin—the prescriber will contact you to discuss alternative options or advise you to see your GP for further assessment.

Safe Alternatives to Vardenafil When Taking Erythromycin

If you are taking erythromycin and need treatment for erectile dysfunction, your prescriber may consider alternative PDE5 inhibitors that have a different interaction profile. Sildenafil (generic Viagra) is also affected by CYP3A4 inhibitors, but the interaction is less severe than with vardenafil, and a lower starting dose (25 mg) can often be used safely under medical supervision [3]. Tadalafil (generic Cialis) is another option; when taken with potent CYP3A4 inhibitors, the maximum recommended dose is reduced, but it can still be prescribed if appropriate [4].

Avanafil (Spedra) is contraindicated with potent CYP3A4 inhibitors, so it would not be suitable if you are taking erythromycin [6]. Your prescriber will weigh up the risks and benefits of each option based on your individual circumstances, the duration of your antibiotic course, and the severity of your ED. In some cases, it may be safest to wait until you have finished the course of erythromycin before starting or restarting ED treatment, especially if the infection is short-term.

If you develop a bacterial infection while taking vardenafil, inform your GP or prescribing pharmacist so they can choose an antibiotic that does not interact significantly. Azithromycin, for example, has a much weaker effect on CYP3A4 and may be a safer choice if clinically appropriate for your infection. Always be open about all the medicines you are taking—this helps your healthcare team to make the best decisions for your safety and wellbeing.

Practical Advice and Warning Signs to Watch For

If you are prescribed vardenafil, keep an up-to-date list of all your medicines and show it to any doctor, dentist, or pharmacist who treats you. If you are given a new prescription for an antibiotic or any other medicine, check whether it is safe to take with vardenafil—do not assume that all antibiotics are the same. If in doubt, contact your pharmacist or prescriber before taking the new medicine.

Be alert to warning signs that may indicate a problem. Seek urgent medical help (call 999 or go to A&E) if you experience an erection lasting more than four hours (priapism), sudden loss of vision in one or both eyes, sudden decrease or loss of hearing (which may be accompanied by ringing in the ears or dizziness), or chest pain during sexual activity [5]. These are rare but serious side effects that require immediate attention.

If you notice more common side effects such as severe headache, dizziness, or visual disturbances (such as blurred vision or increased sensitivity to light) after taking vardenafil, especially if you have recently started or changed another medicine, contact your GP or pharmacist for advice. Do not take more vardenafil than prescribed, and do not take it more than once in 24 hours. Avoid drinking large amounts of alcohol, as this can make side effects worse and reduce the effectiveness of the treatment [5].

When to See Your GP

Erectile dysfunction can be an early warning sign of underlying health conditions such as heart disease, high blood pressure, or diabetes [1]. If you are experiencing ED for the first time, or if it is getting worse, make an appointment with your GP for a full assessment. Your doctor can check for underlying causes, review your medicines, and refer you for specialist advice if needed. Treating the underlying condition may improve your ED and your overall health [2].

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 30 October 2026]
2. National Institute for Health and Care Excellence. (n.d.). Erectile dysfunction. Clinical Knowledge Summaries. https://cks.nice.org.uk/topics/erectile-dysfunction/ [accessed 30 October 2026]
3. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 30 October 2026]
4. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 30 October 2026]
5. Joint Formulary Committee. (n.d.). Vardenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/vardenafil/ [accessed 30 October 2026]
6. Joint Formulary Committee. (n.d.). Avanafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/avanafil/ [accessed 30 October 2026]

Information on this page is for educational purposes only and is not medical advice. Prescription treatments require clinical assessment by a UK-registered prescriber. Always consult a qualified healthcare professional before starting or changing any medication.