6 Cephalexin Interactions You Should Know About

If you or your child have ever had a bacterial infection, your healthcare provider may have prescribed cephalexin. It’s an affordable, FDA-approved cephalosporin antibiotic that’s widely available in pharmacies across the U.S. 

It’s also pretty versatile. Cephalexin is used to treat a variety of bacterial infections in children and adults, such as skin, bone, and respiratory tract infections. Cephalexin also treats ear, urinary, and reproductive system infections.  

However, if you’ve been handed a prescription for cephalexin, you may be curious if it interacts with any medications, supplements, or foods that are part of your daily routine. It generally has fewer interactions than many other antibiotics, but it still has some notable ones to keep in mind. 

6 cephalexin interactions to know about

Cephalexin doesn’t affect certain liver enzymes (proteins) that are responsible for activating or breaking down medications. This helps limit the number of drug interactions that it has. But cephalexin can be tough on your kidneys, so it may interact with other medications that also affect the kidneys. In fact, your dose of cephalexin may be lowered if you have kidney problems.

Here, we’ll discuss some of the most common interactions with cephalexin you should be aware of. 

Keep in mind: There may be other interactions that aren’t listed here. Always keep an updated list of your prescription and over-the-counter medications. Your healthcare provider and pharmacist can check if any of your medications interact with cephalexin. 

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1. Metformin

Metformin is one of the most popular medications in the U.S. — it’s most commonly used to manage blood sugar levels in people with Type 2 diabetes. Cephalexin can raise the amount of metformin in the body by lowering the amount that’s cleared by the kidneys. 

This interaction is mentioned in cephalexin’s labeling, but there’s not a lot of data about it. One small study found that one dose of cephalexin taken with metformin raised the amount of metformin in the body, but the study authors didn’t conclude what the clinical effects of this were. There isn’t any widely known data that speaks to the effects of multiple cephalexin doses on metformin.  

It’s rare for metformin by itself to cause hypoglycemia (low blood sugar). But in theory, this interaction could lower your blood sugar too much. Your healthcare provider may recommend checking your blood sugar at home more frequently while taking metformin and cephalexin.  

2. Probenecid

Probenecid is a medication that’s used to treat gout. Cephalexin levels in the body can become too high when it’s taken with probenecid. 

Typically, it’s recommended to avoid taking these medications at the same time. Together, the combination can raise the risk of experiencing cephalexin side effects, such as nausea, vomiting, or diarrhea. It can also place added stress on the kidneys — especially if you already have kidney problems. Your healthcare provider may adjust the dose for one or both of these medications if you end up taking them together.  

However, drug interactions sometimes can be used as an advantage. Another FDA-approved use of probenecid is boosting the antibiotic activity of certain penicillin antibiotics. This can make the antibiotic more effective in certain situations. Cephalexin isn’t a penicillin antibiotic, but some studies have also reported that probenecid can boost cephalexin levels. But more research is needed to confirm this effect.

3. Warfarin

Warfarin (Coumadin, Jantoven) is a blood thinner used to treat and prevent blood clots. If you take warfarin, your healthcare provider and pharmacist have likely mentioned that it has a lot of interactions, including interactions with your diet. 

Medications are no exception to this. Many medications can increase the risk of bleeding when used with warfarin. Other medications can cause warfarin to be less effective — raising the risk of a blood clot. 

Cephalexin can worsen the risk of bleeding when used with warfarin. Cephalexin has a lower risk of causing this interaction than other antibiotics, but your healthcare provider may still perform frequent blood tests while you’re taking cephalexin out of caution. This will help them see if your warfarin dose needs to be adjusted. Make sure to watch for any signs of bleeding or bruising.   

4. Certain live vaccines (cholera, typhoid, BCG)

Antibiotics — including cephalexin — can cause live oral typhoid (Vivotif) and cholera (Vaxchora) vaccines to be less effective. The live BCG vaccine for tuberculosis may also interact with antibiotics. These interactions could cause your body to not build up a strong enough immune response to fight cholera, typhoid fever, or tuberculosis infections.   

If you’re taking cephalexin and need these vaccines, it’s best to separate them. This will help make sure you get the most vaccine benefits. Wait to get the Vivotif vaccine for at least 72 hours after finishing your last dose of cephalexin. And after finishing cephalexin, wait at least 14 days to get the Vaxchora vaccine. Your healthcare provider and pharmacist can help answer any travel vaccine questions you may have.    

While not typically used in the U.S., the BCG vaccine is given in many countries to prevent tuberculosis. Antibiotics — including cephalexin — may cause the BCG vaccine to be less effective by lowering the immune response. Research hasn’t shown a recommendation for how to separate antibiotics from the BCG vaccine. But your healthcare provider may decide to separate them out so you get the full vaccine benefits.  

5. Zinc

Zinc is a mineral found in a variety of dietary supplements at your local pharmacy, and it comes in various doses. 

Studies show that zinc can lower the absorption of cephalexin in the body. This may cause cephalexin to be less effective at fighting infections. Separating zinc and cephalexin can help prevent this interaction. Taking zinc — or multivitamins that contain zinc — at least 3 hours after your cephalexin helps your body absorb cephalexin better.     

6. Alcohol

Have you ever wondered whether you can have an alcoholic beverage if you’re taking an antibiotic? It depends on the antibiotic. 

While there isn’t a direct interaction between cephalexin and alcohol, they both can have similar side effects. These include nausea, vomiting, and diarrhea. Using the two together could make your side effects even worse. And certain cephalosporins — like cefotetan and cefoperazone — can cause a disulfiram-like reaction when taken with alcohol. These antibiotics are chemically related to cephalexin. This can cause many side effects that can be harmful:

• Nausea

• Vomiting

• Facial flushing

• Face and mouth swelling 

• Low blood pressure   

In general, it’s best to avoid alcohol while you have an infection. Alcohol can also affect the immune system and make it harder for you to heal from an infection.   

When should I contact my healthcare provider about a cephalexin interaction?

Let your healthcare provider know if you experience any new or worrisome side effects while taking cephalexin, such as nausea, vomiting, or diarrhea. These are normal side effects of cephalexin and most go away once your prescription is finished. But in some cases, they could be possible signs of an interaction. 

Specific medications have their own considerations too, especially warfarin. If you’re taking warfarin, it’s a good idea to receive blood checks more frequently while taking cephalexin. This can help determine whether your warfarin dose needs to be changed during or after treatment with cephalexin. Contact your healthcare provider if you notice any signs of bleeding or bruising.  

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Written by:

Jennifer Gershman, PharmD, CPh, PACS

Jennifer Gershman, PharmD, is a licensed pharmacist in Florida. She has worked in the pharmacy industry for more than 15 years and is currently a medical writer.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

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