If you have hepatitis C, you have an infection in your liver. It’s caused by the hepatitis C virus, which is very contagious. Your doctor may have suggested treatment with a new drug called Harvoni. It’s a single tablet that contains two drugs: ledipasvir and sofosbuvir. This medication is taken by mouth once per day. Harvoni cures hepatitis C in most patients in just 12 weeks. Previous hepatitis C treatments took longer and required several tablets and injections. They also caused more severe side effects and had lower cure rates.

When considering any new drug, you may wonder about possible interactions with other drugs you’re taking. For instance, if you’re taking antibiotics, you may wonder if Harvoni is still safe to use. Harvoni was approved by the U.S. Food and Drug Administration in 2014, but doctors are still hearing from patients about new effects of the drug. Here’s what we know about taking Harvoni and antibiotics together.

The short answer is, it depends on the antibiotic. Most antibiotics are fine to use with Harvoni, but some can cause interactions.

A drug interaction is when one drug changes the way another drug works. This can be harmful or prevent the drug from working well. Like a lot of drugs, Harvoni has many drug interactions, including with some important antibiotics. These include antibiotics mainly used to treat tuberculosis (TB).

The interaction between these TB drugs and Harvoni involves your liver. Your liver helps your body process these drugs, like it does with any drugs you take. But when your liver processes these antibiotics, the drugs change the way your liver works. Over time, they make your liver work faster. This means that any drugs you take are processed more quickly. This reduces the amounts of those drugs in your body. As a result, you’ll need a larger dose of the drugs to get the same effect.

The TB antibiotics that cause interactions include:

  • Rifabutin (Mycobutin). This drug is used to treat TB and several other kinds of infections. These other infections include mycobacterium avium complex (MAC), an infection that may affect people with HIV.
  • Rifampin (Rifadin). This drug is combined with other drugs to treat TB. It’s also sometimes used to treat infections in artificial heart valves, nasal or joint infections, or infections such as leprosy or meningitis.
  • Rifapentine (Priftin). This drug is combined with other drugs to treat TB.

Do not take any of these antibiotics with Harvoni. They may reduce the amount of Harvoni in your body, making the drug less able to fight hepatitis C.

Harvoni is a new drug, so we’re still learning whether other antibiotics also interact with it. The most likely are antibiotics already known to interact with other drugs. For instance, erythromycin, clarithromycin, and vancomycin often interact with many other drugs. But so far, there have been no reports of Harvoni interacting with these antibiotics.

If you have hepatitis C and you’re considering taking Harvoni, your doctor will do a thorough check for possible drug interactions. They will do complete blood testing and a full review of your medical records. Be sure to tell them about all the drugs you take. This includes prescription and over-the-counter drugs and any supplements. Your doctor, as well as your pharmacist, will have the latest information about any drug interactions that may occur with Harvoni. They can tell you which drugs to avoid during your treatment with Harvoni.

If you’re being treated with antibiotics, be sure your doctor knows before you start taking Harvoni. Your infection may need to clear up before you take Harvoni, or you may need to take a different antibiotic. This small step can help ensure that your treatment with Harvoni is successful.