Sildenafil and Rifabutin: Can You Take Them Together?

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Key takeaways

• Rifabutin can reduce sildenafil effectiveness by speeding up how quickly your liver breaks it down
• The combination is not dangerous, but sildenafil may not work as well during rifabutin treatment
• Do not increase your sildenafil dose without consulting your prescriber
• All PDE5 inhibitors are affected similarly; alternatives like alprostadil may be considered
• Never stop rifabutin without medical advice—complete your full antibiotic course

What is sildenafil and how does it work?

Sildenafil is a prescription medicine used to treat erectile dysfunction (ED) in men. 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 [3]. Sildenafil is the active ingredient in Viagra and is available in generic forms at lower cost.

The medicine comes in three strengths: 25mg, 50mg, and 100mg tablets. You typically take sildenafil about one hour before sexual activity, and it can remain effective for up to four hours [3]. It's important to understand that sildenafil only works when you are sexually stimulated—it does not cause an automatic erection.

Sildenafil is broken down in your liver by enzymes, particularly one called CYP3A4. This is where the interaction with rifabutin becomes relevant, as rifabutin affects how quickly this enzyme works. At Cured Pharmacy, sildenafil is available after an online consultation reviewed by a UK prescriber, who will check all your current medicines for potential interactions.

What is rifabutin and why is it prescribed?

Rifabutin is an antibiotic medicine used to treat and prevent certain bacterial infections, particularly mycobacterial infections such as Mycobacterium avium complex (MAC). It is sometimes prescribed for people with weakened immune systems, including those with HIV, or as part of treatment for tuberculosis when standard antibiotics are not suitable.

This antibiotic works by stopping bacteria from making essential proteins they need to survive and multiply. Rifabutin is usually taken once daily, and treatment courses can last several weeks or months depending on the infection being treated.

Rifabutin belongs to a class of medicines called rifamycins, which are known to interact with many other drugs. It is what pharmacists call a CYP3A4 inducer, meaning it speeds up the activity of liver enzymes that break down other medicines. This can make some medicines less effective because they are removed from your body more quickly than usual.

How rifabutin affects other medicines

When rifabutin increases the activity of liver enzymes, medicines that rely on those enzymes for breakdown are processed faster. This means lower levels of the medicine remain in your bloodstream, potentially reducing its effectiveness. This interaction affects many types of medicine, including hormonal contraceptives, some heart medicines, and erectile dysfunction treatments like sildenafil.

At a glance

How do sildenafil and rifabutin interact?

The interaction between sildenafil and rifabutin occurs because rifabutin speeds up the liver enzymes (particularly CYP3A4) that break down sildenafil [3]. When these enzymes work faster, sildenafil is removed from your body more quickly, which means lower levels of the medicine remain in your bloodstream. This can reduce how well sildenafil works for treating erectile dysfunction.

Unlike some medicines that increase sildenafil levels and require dose reductions, rifabutin has the opposite effect—it may make sildenafil less effective. This is similar to the effect seen with other CYP3A4 inducers such as rifampicin, carbamazepine, phenytoin, and St John's wort.

The good news is that this interaction is not dangerous in terms of safety—rifabutin does not cause sildenafil levels to rise to unsafe amounts or increase the risk of serious side effects. The main concern is reduced effectiveness rather than toxicity. Your prescriber will consider this interaction when deciding whether sildenafil is the right choice for you while you are taking rifabutin, or whether an alternative approach might be more suitable.

What happens in your body

Normally, when you take sildenafil, it is absorbed into your bloodstream and then gradually broken down by liver enzymes over several hours. Rifabutin 'revs up' these enzymes, so they work faster and more efficiently. As a result, sildenafil is cleared from your system more quickly, potentially before it has had the chance to produce the desired effect during sexual activity.

What your prescriber will check before prescribing sildenafil and rifabutin together

When you request sildenafil through Cured Pharmacy's online consultation, you will be asked to list all medicines you currently take, including antibiotics like rifabutin. A UK-registered prescriber will review your medical history and current treatments to assess whether sildenafil is safe and likely to be effective for you.

Your prescriber will consider several factors: how long you will be taking rifabutin, whether the course is short-term or long-term, and whether there are alternative ED treatments that might work better during your antibiotic treatment. They will also check for any other medicines or health conditions that could affect your suitability for sildenafil [2].

If sildenafil is prescribed while you are taking rifabutin, your prescriber may discuss realistic expectations about effectiveness. In some cases, they might suggest a different PDE5 inhibitor, adjust the timing of doses, or recommend waiting until your rifabutin course is complete if the infection is being treated short-term. The prescriber will also ensure you are not taking any medicines that are absolutely contraindicated with sildenafil, such as nitrates, nicorandil, or riociguat [3].

Practical advice if you are taking both medicines

If your prescriber approves sildenafil while you are taking rifabutin, it is important to take both medicines exactly as directed. Do not increase your sildenafil dose on your own in an attempt to overcome the reduced effectiveness—higher doses increase the risk of side effects without necessarily improving results.

Be aware that sildenafil may not work as well as expected while you are on rifabutin. If you find the medicine is not effective, speak to your prescriber rather than taking extra tablets. They can review your treatment and discuss alternatives. Other PDE5 inhibitors such as tadalafil, vardenafil, or avanafil are also affected by CYP3A4 inducers, so switching may not solve the problem, but your prescriber can advise on the best approach for your situation.

Do not stop taking rifabutin without consulting the doctor who prescribed it, even if you are concerned about the interaction with sildenafil. Rifabutin is usually prescribed for serious infections that require a full course of treatment. If erectile dysfunction treatment is a priority during this time, discuss your concerns with your prescriber—they may be able to suggest alternative strategies or reassure you about what to expect once your antibiotic course is finished.

Timing and expectations

The effect of rifabutin on liver enzymes builds up over days to weeks and can persist for some time after you stop taking the antibiotic. This means sildenafil effectiveness may gradually improve in the weeks following the end of your rifabutin course. Your prescriber can advise on when to expect normal effectiveness to return.

Other erectile dysfunction treatments and rifabutin interactions

All PDE5 inhibitors—including tadalafil (Cialis), vardenafil (Levitra), and avanafil (Spedra)—are broken down by the same liver enzymes affected by rifabutin [4][5][6]. This means rifabutin can reduce the effectiveness of these medicines in a similar way to sildenafil. Switching from one PDE5 inhibitor to another is unlikely to overcome the interaction.

If you are taking rifabutin long-term and oral ED medicines are not working well, your doctor may discuss alternative treatments. These include alprostadil, which is available as a cream (Vitaros) applied to the tip of the penis or as an injection (Caverject) into the side of the penis [7]. Because alprostadil works locally rather than being absorbed and processed by the liver in the same way, it is not affected by rifabutin's enzyme-inducing effects.

Eroxon, a topical gel medical device available without prescription, works through a physical cooling-then-warming effect rather than through systemic absorption, so it is not affected by rifabutin. Your pharmacist or prescriber can discuss whether any of these alternatives might be suitable for you. Remember that erectile dysfunction can be an early warning sign of heart disease or diabetes, so if ED is a new problem, it is important to see your GP for a full assessment [1].

When to get urgent help

• Erection lasting more than 4 hours (priapism)—go to A&E immediately
• Sudden loss of vision in one or both eyes—seek urgent medical attention
• Sudden decrease or loss of hearing—contact your doctor or NHS 111 immediately
• Chest pain during or after sexual activity—call 999 and do not take more sildenafil

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

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