Vardenafil and Primidone: Can You Take Them Together?

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At a glance

What is vardenafil and primidone used for?

Vardenafil (also known by the brand name Levitra) is a prescription medicine used to treat erectile dysfunction in men [5]. It belongs to a group of medicines called PDE5 inhibitors, which work by increasing blood flow to the penis during sexual stimulation. Vardenafil is available in 5mg, 10mg, and 20mg tablets, and you typically take it about 25 to 60 minutes before sexual activity [5]. Like all PDE5 inhibitors, vardenafil only works when you're sexually aroused—it doesn't cause an automatic erection.

Primidone is an anticonvulsant medicine prescribed to control epileptic seizures [12]. It works by calming electrical activity in the brain that can trigger seizures. Primidone is converted in the body to phenobarbital, another anticonvulsant, which is why it's particularly effective for certain types of epilepsy. People usually take primidone regularly, often two or three times a day, to maintain steady seizure control. It's important to take primidone exactly as your doctor prescribes, as stopping suddenly can trigger seizures.

How does the interaction between vardenafil and primidone work?

Primidone is what pharmacists call an enzyme inducer. This means it speeds up the activity of certain liver enzymes—specifically the CYP3A4 enzyme system—that break down many medicines, including vardenafil [5]. When these enzymes work faster, vardenafil is cleared from your body more quickly than usual. As a result, the levels of vardenafil in your bloodstream may be lower, and the medicine may not work as well or for as long as it would in someone not taking primidone.

This type of interaction is called a pharmacokinetic interaction because it affects how your body processes the medicine, rather than how the medicine acts in your body. The good news is that this interaction doesn't make the combination dangerous—there's no increased risk of serious side effects when you take vardenafil and primidone together. The main concern is simply that vardenafil may be less effective at helping you achieve and maintain an erection suitable for sexual activity.

The effect of enzyme induction builds up gradually over a few weeks after you start taking primidone, and it can persist for several weeks after you stop. This means the interaction is most significant in people who take primidone regularly for ongoing seizure control, rather than those who've only taken it briefly.

What does your prescriber check before prescribing vardenafil with primidone?

When you request vardenafil through an online consultation at Cured Pharmacy, you'll be asked to list all your current medicines, including primidone and any other anticonvulsants. A UK-registered prescriber will review your medical history and medication list to assess whether vardenafil is suitable for you [2]. They'll consider whether the potential reduction in vardenafil's effectiveness due to primidone means you might benefit from a higher starting dose, or whether a different ED treatment might work better for you.

Your prescriber will also check for any other medicines or health conditions that could interact with vardenafil. For example, vardenafil must never be taken with nitrates (such as GTN spray), nicorandil, riociguat, or recreational drugs called poppers, as these combinations can cause a dangerous drop in blood pressure [5]. If you take medicines for high blood pressure or an enlarged prostate (alpha-blockers like tamsulosin or doxazosin), your prescriber will ensure you're on a stable dose and may recommend starting vardenafil at the lowest strength.

Why it's important to declare all your medicines

Even if you think a medicine is unrelated to erectile dysfunction, it's essential to list everything you take—including over-the-counter medicines, herbal supplements like St John's wort, and any medicines you take occasionally. Enzyme inducers like primidone, carbamazepine, phenytoin, and rifampicin can all reduce the effectiveness of vardenafil [5]. On the other hand, some medicines (such as certain antibiotics and antifungals) can increase vardenafil levels and raise the risk of side effects. Your prescriber needs the full picture to make a safe, effective recommendation.

What you need to know

• Vardenafil and primidone can be taken together safely, but primidone may reduce vardenafil's effectiveness.
• Primidone speeds up liver enzymes that break down vardenafil, lowering its levels in your bloodstream.
• Your prescriber may recommend a higher dose or alternative ED treatment if vardenafil isn't effective enough.
• Never stop primidone without medical advice, as this can trigger seizures.
• Always declare all medicines during your consultation so your prescriber can assess safety and effectiveness.

Practical advice for taking vardenafil and primidone together

If your prescriber approves vardenafil while you're taking primidone, you can take both medicines on the same day—there's no need to separate the doses by a specific number of hours. However, because primidone may make vardenafil less effective, you might find that the usual starting dose (10mg) doesn't work as well for you as it does for other men. If this happens, don't simply take more tablets on your own. Instead, contact your prescriber to discuss whether increasing the dose to 20mg (the maximum licensed dose) might be appropriate [5].

Take vardenafil about 25 to 60 minutes before you plan to have sex, and remember that it only works when you're sexually stimulated [5]. Avoid heavy or high-fat meals shortly before taking vardenafil, as these can delay how quickly the medicine is absorbed. Limit alcohol to one or two units, because drinking heavily can make erectile dysfunction worse and add to the blood-pressure-lowering effect of vardenafil, increasing the risk of dizziness.

Never stop or change the dose of primidone without speaking to your doctor, even if you think it's affecting your ED treatment. Stopping primidone suddenly can trigger seizures. If you feel vardenafil isn't working well enough, your prescriber can explore other options, such as switching to a different PDE5 inhibitor or considering alternative ED treatments.

Are there alternative ED treatments if vardenafil and primidone don't work well together?

If you find that vardenafil isn't effective enough while you're taking primidone, there are other licensed ED treatments available. All the oral ED medicines—sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra), and avanafil (Spedra)—are PDE5 inhibitors and are broken down by the same liver enzymes, so primidone may reduce the effectiveness of all of them to some degree [3][4][5][6]. However, people respond differently to each medicine, and some men find one PDE5 inhibitor works better for them than another, even when taking an enzyme inducer.

Tadalafil has a longer duration of action (up to 36 hours) and is also available as a low-dose daily tablet (2.5mg or 5mg), which some men prefer because it allows for more spontaneity [4]. Avanafil (Spedra) works faster than other PDE5 inhibitors, taking effect in as little as 15 to 30 minutes [6]. Your prescriber can discuss which option might suit your lifestyle and whether a higher dose or a different medicine could overcome the enzyme-inducing effect of primidone.

If oral medicines don't work well enough, other prescription treatments are available, such as Vitaros (alprostadil cream applied to the tip of the penis) or Caverject (alprostadil injection) [7]. These work by a different mechanism and are not affected by enzyme inducers like primidone. Your GP or a specialist can discuss these options with you if needed.

When to see your GP about erectile dysfunction

When to get urgent help

• Erection lasting longer than 4 hours (priapism)—go to A&E immediately
• Sudden loss of vision in one or both eyes—seek urgent medical help
• Sudden decrease or loss of hearing—contact a doctor straight away
• Chest pain during or after sex—stop activity and seek urgent advice; do not take nitrates
• Severe dizziness or fainting after taking vardenafil—contact your GP or call 111

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

What to watch for and when to seek help with vardenafil and primidone

Most men tolerate vardenafil well, even when taking it with primidone. Common side effects of vardenafil include headache, flushing, nasal congestion, and indigestion, which are usually mild and short-lived [5]. Because primidone may reduce vardenafil levels, you're not at increased risk of side effects from this interaction. However, you should still be aware of the warning signs that need urgent medical attention.

Seek immediate help by calling 999 or going to A&E if you experience an erection that lasts longer than four hours (priapism), sudden loss of vision in one or both eyes, or sudden decrease or loss of hearing [5]. If you develop chest pain during or after sex, stop sexual activity and seek urgent medical advice—do not take GTN spray or any nitrate medicine if you've taken vardenafil within the last 24 hours, as this combination is dangerous [5].

If you notice that vardenafil isn't working at all, or if you experience severe dizziness or fainting, contact your prescriber or GP. Don't be tempted to take more than one tablet in 24 hours or to combine vardenafil with another ED medicine, as this increases the risk of side effects without improving effectiveness. Your healthcare professional can review your treatment and suggest safer alternatives.

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