Warnings

Keflex

Medically Reviewed by HaVy Ngo, Pharm.D.

Last Reviewed: Jun 09, 2022

Warnings

What are the risks of taking Keflex?

Keflex can cause serious health problems in certain groups of people. You should talk to your healthcare provider if you have any concerns or other treatment options.
Development of drug-resistant bacteria:

Risk Factor: taking Keflex for non-bacterial infection; skipping doses

Like other antibiotics, Keflex is effective against certain bacteria. Taking antibiotics when not indicated can lead to drug-resistant bacteria, a public health concern. Drug-resistant bacteria are much harder to treat. Not taking antibiotics as prescribed, skipping doses, and not finishing the whole course of antibiotics can also increase this risk.

Development of new infection:

Risk Factor: prolonged use of Keflex
Prolonged use of Keflex or any other antibiotics may result in the overgrowth of nonsusceptible organisms — This is called a “superinfection.” If you develop a fever or don’t feel better after finishing the entire course of antibiotics, let your doctor know right away.

Hypersensitivity reactions (a serious allergic reaction):

Risk Factor: History of allergic reaction to cephalexin, cephalosporins, and penicillins.
Cephalexin can cause severe allergic reactions presenting with rash, trouble breathing, or swelling of the face and throat. If you had an allergic reaction to any cephalosporin or penicillin antibiotic, let your healthcare provider know before taking Keflex. Another type of antibiotic may be a safer choice for you. If you experience these symptoms while taking Keflex, stop taking Keflex and seek emergency medical help, as an untreated allergic reaction can be life-threatening.

Clostridium Difficile-associated diarrhea (CDAD):

Risk Factor: long-term use of Keflex; recent use of other antibiotics; using multiple antibiotics; weakened immune system.
In some rare cases, a bacteria called Clostridioides difficile (commonly known as C. diff) causes severe diarrhea because Keflex (like all other antibiotic medicines) gets rid of the good bacteria in your gastrointestinal tract. CDAD may cause mild diarrhea to life-threatening inflammation of the colon. If you develop severe diarrhea that can be watery and bloody, let your doctor know immediately. Careful medical history is necessary as CDAD can happen months after the last dose of Keflex.

Seizures:

Risk Factor: history of kidney disease
Like other cephalosporins, Keflex can trigger seizures. If you have kidney disease, your body does not clear Keflex out as efficiently as others with normal kidney function. Your doctor or pharmacist will adjust your dose based on your kidney function.

What should I tell my doctor before starting Keflex?

Tell your doctor if you have:

An allergy to penicillins, cephalosporins, and other antibiotics
Liver or kidney disease
Chronic diarrhea that may be caused by intestinal diseases like colitis (inflammation of the colon)
An allergy to any ingredients in Keflex oral capsules, tablets, or suspension — Ask your pharmacist for the ingredient list.

Tell your doctor if you are pregnant or plan to become pregnant. Keflex is excreted into human breast milk. Tell your doctor that you are breastfeeding before taking Keflex.

What proper medical care should I take while on Keflex?

Keflex can cause nausea and vomiting. Taking Keflex with food can help with stomach upset.

Keflex can cause C.Diff associated diarrhea. You should let your doctor know if you have severe diarrhea before taking any anti-diarrhea medicine, even if diarrhea occurs months after the last dose of Keflex.

Finish the course of antibiotics as prescribed without skipping doses to avoid antibiotic-resistant bugs.

What drugs can interact with Keflex?

Let your doctor know of all prescription medications you take, especially the following drugs, as they can interact with Keflex:

Do not take lisinopril with the following medicines:

Metformin (Glucophage) - the interaction between Keflex and metformin can increase the blood level of metformin.
Probenecid (Benemid) - Co-administration of probenecid and Keflex is not recommended because probenecid blocks the excretion of Keflex through the kidney.

This is not a complete list. All your other drugs, including prescription drugs, over-the-counter medicines, herbal supplements, and vitamins, may interact with Keflex. Not all potential drug interactions are listed in this guide. It is highly recommended to keep a list of all the drug products you are using (prescriptions, over-the-counter products, herbal supplements, natural products, and vitamins) and share it with your doctor and pharmacist.

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