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Cephalexin oral forms side effects: A detailed guide

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Cephalexin oral forms are prescribed for treating certain infections caused by bacteria. They’re a kind of antibiotic drug called cephalosporin. Cephalexin may cause mild or serious side effects, including diarrhea caused by Clostridium difficile infection.
Medically reviewed by Purva Singla, PharmD
Updated on

Specifically, the Food and Drug Administration (FDA) has approved cephalexin oral forms for use in adults and some children. They treat specific kinds of the following infections caused by bacteria:

  • respiratory infections
  • ear infections
  • skin infections
  • bone infections
  • urinary or genital infections

This article describes possible side effects of cephalexin oral forms. You’ll also find information on cost savings and coupon options for cephalexin.

Cephalexin oral forms are generic medications. They’re not available in brand-name versions.

You can explore this overview article to learn more about cephalexin oral forms, including their uses, dosages, and more.

More common side effects of cephalexin

Cephalexin oral forms may cause mild or serious side effects. Below are some of the more common side effects of this medication.

Commonly reported side effects of cephalexin oral forms include:

  • nausea
  • vomiting
  • indigestion (upset stomach)
  • belly pain
  • diarrhea*

* To learn more about this side effect, see the “Side effects of cephalexin in detail” section below.

Mild side effects of cephalexin

Cephalexin may cause certain mild side effects. Most often, mild side effects are temporary and can be managed easily. Tell your doctor or pharmacist if you have side effects that don’t go away or become bothersome.

Mild side effects of cephalexin oral forms occurred in studies of cephalexin’s oral tablet, powder for suspension, and oral capsule. They include:

  • nausea and vomiting
  • indigestion (upset stomach)
  • belly pain
  • anal or genital itching
  • vaginal fungal infection
  • dizziness
  • fatigue (low energy)
  • headache
  • confusion or agitation
  • joint problems, including inflammation or pain
  • diarrhea*
  • mild allergic reaction*

* To learn more about this side effect, see the “Side effects of cephalexin in detail” section below.

Cephalexin oral forms may cause more mild side effects than those listed above. For details, see the prescribing information for cephalexin’s oral tablet, powder for suspension, and oral capsule.

Serious side effects of cephalexin

Cephalexin may cause certain serious side effects. If you have any serious side effects from cephalexin oral forms, call your doctor right away. But if you think you’re having a medical emergency or your side effects feel life threatening, act immediately. Call 911 or a local emergency number, or go to the nearest emergency room.

After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Visit MedWatch’s website if you’d like to notify the FDA about a side effect you’ve had with cephalexin oral forms.

Serious side effects of cephalexin oral forms occurred in studies of cephalexin’s oral tablet, powder for suspension, and oral capsule. They include:

* To learn more about this side effect, see the “Side effects of cephalexin in detail” section below.

Common questions about side effects of cephalexin

Here are answers to some common questions about side effects of cephalexin oral forms. If you have other questions, talk with your doctor or pharmacist.

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Can cephalexin 500 mg cause side effects different from the drug’s other strengths?

No, a 500-mg dose of cephalexin isn’t expected to cause side effects different from a 250-mg dose. The studies of cephalexin’s oral tablet, powder for suspension, and oral capsule didn’t note different side effects between dosage strengths. That said, your risk of side effects from a drug usually increases if you take a higher dose.

To learn more about your risk of side effects from cephalexin, talk with your doctor or pharmacist.

How do the side effects of cephalexin in adults compare with those seen in children?

Side effects of cephalexin in adults and children are expected to be the same. For details, see the prescribing information for cephalexin’s oral tablet, powder for suspension, and oral capsule.

Ask your child’s doctor for more information about cephalexin and your child’s risk of side effects.

Does cephalexin cause long-term side effects?

Cephalexin isn’t believed to cause long-term side effects. Long-term side effects weren’t noted in the studies of cephalexin’s oral tablet, powder for suspension, and oral capsule.

That said, cephalexin is an antibiotic and can cause diarrhea that may be serious. (This is a known side effect of nearly all antibiotic drugs, although it’s rare.)  

It’s important to know that cephalexin can cause some serious side effects. Examples include diarrhea caused by Clostridium difficile (C. diff) infection and severe allergic reaction. In rare reports, C. diff diarrhea has occurred later than 2 months after taking the last dose of an antibiotic. (See the prescribing information for cephalexin’s oral tablet, powder for suspension, and oral capsule.) In extreme cases, these serious conditions can be life threatening or even fatal.

For more information on these serious side effects, review the “Side effects of cephalexin in detail” section below. It discusses ways to help treat these side effects if they do occur. You can also talk with your pharmacist or doctor to learn more.

Warnings for cephalexin

Below are some factors you may want to discuss with your doctor before taking cephalexin oral forms.

Warnings

It may not be safe for you to take cephalexin oral forms if you have specific health conditions. These are sometimes called drug-condition interactions. Other things may also affect whether cephalexin oral forms are a safe treatment option for you.

Before taking cephalexin oral forms, tell your doctor about your health and medications you take. Things to consider include those listed below.

Kidney problems. Cephalexin may not be safe to take if you have a serious kidney problem. An example is advanced chronic kidney disease (CKD). Your kidneys remove cephalexin from your body after you take a dose. But if you have a kidney problem, your body may not remove cephalexin completely. This can cause the level of the drug in your body to increase. In turn, that raises your risk of side effects from the drug.

Cephalexin also can cause kidney problems as a side effect. If you already have a kidney problem, your condition could worsen by taking cephalexin.

Additionally, if you have a kidney problem, you may be at higher risk of seizures by taking cephalexin.

It’s usually safe to take cephalexin if you have a mild or moderate kidney problem. But your doctor may prescribe a dose that’s lower than the recommended dose.

Seizures. If you experience seizures, be sure to let your doctor know before starting treatment with cephalexin. This includes seizures caused by epilepsy. In rare cases, the drug can cause seizures as a side effect. For example, if you have a kidney problem, you may be at higher risk of seizures by taking cephalexin.

Your doctor can help determine whether cephalexin is safe for you to take.

Allergic reaction. If you’ve had an allergic reaction to any cephalexin oral form or its ingredients, your doctor will likely not prescribe this medication. Ask them about other treatment options that may be better for you.

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Cephalexin and pregnancy

It’s not known whether cephalexin is safe to take during pregnancy. Studies haven’t tested the drug in pregnant people.

Talk with your doctor about safe treatments for your infection if you’re pregnant or planning a pregnancy.

Cephalexin and breastfeeding

Cephalexin passes into breast milk. In rare reports, mild side effects occurred in children who were breastfed by a parent having cephalexin treatment.

You and your doctor can discuss whether it’s safe to breastfeed during treatment. If you both agree that it is, be sure to monitor your child for diarrhea or infection. Your doctor can advise you on signs to look for in your child.

Cephalexin and alcohol

Cephalexin oral forms aren’t known to interact with alcohol.

But alcohol and cephalexin can cause side effects that are similar. Examples include diarrhea, indigestion (upset stomach), and headache. So taking the two together could raise your risk of these side effects.

If you drink alcohol, talk with your doctor about whether it’s safe to consume it during your treatment with cephalexin oral forms.

Coupon for cephalexin

Visit this page to access Optum Perks coupons and get price estimates for cephalexin when you use the coupons. These coupons can provide significant savings on your prescription costs. 

Note: Optum Perks coupons cannot be used with any insurance copays or benefits.

Side effects of cephalexin in detail

Below you’ll find details on some of the side effects of cephalexin oral forms.

Diarrhea

Mild diarrhea is the most common mild side effect reported in studies of cephalexin’s oral tablet, powder for suspension, and oral capsule.

Symptoms of diarrhea include:

  • loose, watery stools
  • frequent bowel movements
  • stomach cramping

In rare cases, treatment with cephalexin can lead to a Clostridium difficile (C. diff) infection. This can result in serious or life threatening diarrhea. Read the “Clostridium difficile (C. diff) infection” section below to learn more.

Ways to manage

Mild diarrhea should go away once treatment with cephalexin is completed. (Cephalexin is usually taken short term.) If you have diarrhea that bothers you during treatment, call your doctor. They can advise you on the best way to treat your symptoms. This may include the following:

  • Staying hydrated.
  • Taking an over-the-counter (OTC) medication if it’s safe for you to take it. An example of an OTC medication is Imodium A-D.
  • Taking a probiotic if your doctor recommends it. Probiotics boost helpful bacteria in your gut. This helps balance your digestive tract health and reduces diarrhea symptoms.

During cephalexin treatment, tell your doctor if you have bloody or very watery diarrhea. This could indicate a more serious condition, such as an infection.

Clostridium difficile (C. diff) infection

While it occurs rarely, taking cephalexin can result in a C. diff infection. This is a known side effect of nearly all antibiotic drugs. (Cephalexin is an antibiotic drug.) Although these infections usually are mild, they can be severe. In extreme cases, a C. diff infection can be life threatening.

Antibiotics such as cephalexin destroy bacteria in the body. While they’re intended to destroy “bad” bacteria, they also can destroy some “good” bacteria. “Good” bacteria have the main responsibility of keeping the gut healthy, while “bad” bacteria can cause infection. Destroying “good” bacteria can cause C. diff bacteria in the gut to grow out of control. This can result in a C. diff infection.

Symptoms of a C. diff infection include:

  • diarrhea, which can be severe
  • cramping and pain in your belly
  • a general unwell feeling
  • nausea
  • loss of appetite

Rarely, C. diff infection can occur later than 2 months after your last dose of cephalexin. But it is most likely to occur during treatment.

Ways to manage

If you think you have symptoms of a C. diff infection during cephalexin treatment, call your doctor immediately. They will likely advise you to stop taking cephalexin right away. They can also advise you on the best treatment for your symptoms. Serious C. diff infection can require treatment in a hospital, but this isn’t common.

Blood cell problems

Although these side effects are rare, blood cell problems can occur with cephalexin treatment.

Blood cell problems were reported in studies of cephalexin’s oral tablet, powder for suspension, and oral capsule. These include the following.

Thrombocytopenia (low platelet count). In mild cases of thrombocytopenia, people often don’t have symptoms. But in severe cases, people may experience excessive bleeding.

Neutropenia (low neutrophil count). Neutropenia usually doesn’t cause symptoms that you would notice, but it does raise the risk of infection.

Hemolytic anemia. With hemolytic anemia, you have a low red blood cell count. Symptoms may include:

  • fatigue (low energy)
  • confusion
  • pale-looking skin
  • weakness, dizziness, or lightheadedness

Ways to manage

Your doctor likely won’t monitor your blood cell counts while you’re taking cephalexin. This is because it’s usually taken short term. Additionally, these side effects aren’t expected once you complete treatment.

But if you develop symptoms of blood cell problems, your doctor may order a test to check your blood cell counts. If the test indicates a blood cell problem, your doctor will recommend the best way to treat it.

Allergic reaction

For some people, cephalexin oral forms can cause an allergic reaction.

Symptoms can be mild or serious, and they may include:

  • itchiness
  • skin rash
  • swelling under the skin, usually affecting eyelids, lips, hands, or feet
  • swelling of the mouth, tongue, or throat, which can make it hard to breathe
  • flushing (temporary warmth, redness, or deepening of skin color)

Ways to manage

For mild allergic reaction symptoms, such as a mild rash, call your doctor right away. They may recommend treatments to help manage your symptoms. They’ll also let you know whether you should keep taking the medication.

For severe allergic reaction symptoms, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms require immediate medical care because they can become life threatening. If you’ve had a serious allergic reaction to cephalexin oral forms, your doctor may recommend taking a different medication instead.

What to ask your doctor

This article describes common and serious side effects of cephalexin oral forms. If your doctor prescribes this medication, they can discuss possible side effects with you. Let your doctor know if you have concerns or questions about treatment with this medication.

Here’s a list of some possible questions you may want to ask your doctor:

  • Does the kind of infection I’m taking cephalexin to treat affect my risk of side effects?
  • Am I at higher risk of side effects from cephalexin based on my medical history?
  • Do any medications I take raise my risk of side effects from cephalexin?
  • If I’m allergic to penicillin, is it safe for me to take cephalexin?

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.

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