Cephalexin 500 mg: Uses, Dosage, and Important Warnings

Cephalexin 500 mg is a commonly prescribed antibiotic in the cephalosporin family, widely used for treating bacterial infections. Known by brand names such as Keflex and Keftab, it plays a vital role in the fight against infections affecting the skin, respiratory tract, urinary tract, and more. Understanding how cephalexin works, its appropriate dosage, and its possible side effects can help you use it safely and effectively.

In this article, we’ll break down everything you need to know about cephalexin 500 mg, including its uses, dosage instructions, interactions, and what to do if you miss a dose or experience side effects. We’ll also cover how long it takes for cephalexin to work, the typical dosage for various infections, and answer common questions about taking cephalexin with food, dairy, or alcohol.

What Is Cephalexin 500 mg Used For?

Cephalexin 500 mg is prescribed to treat a wide range of bacterial infections, including:

• Urinary tract infections (UTIs)
  
  
• Respiratory tract infections, such as bronchitis and pneumonia
  
  
• Skin infections, including cellulitis and impetigo
  
  
• Bone infections
  
  
• Ear infections (especially in children)
  
  
• Sinus infections and dental abscesses in certain cases
  
  

Doctors may prescribe cephalexin for sinus infection when the bacteria involved are known to respond well to cephalosporins. It’s also commonly used as a UTI antibiotic for individuals allergic to penicillin.

How Does Cephalexin Work?

Cephalexin is a first-generation cephalosporin antibiotic. It works by inhibiting bacterial cell wall synthesis, effectively killing the bacteria and stopping the infection from spreading. Unlike broad-spectrum antibiotics that target a wider range of bacteria, cephalexin is considered narrow-spectrum, which means it targets specific bacteria and is less likely to disrupt your gut flora.

Cephalexin 500 mg Dosage: How Much and How Often?

The dosage of cephalexin 500 mg depends on the type and severity of the infection, as well as the patient’s age, weight, and kidney function. It is typically taken every 6 to 12 hours, and treatment usually lasts 7 to 14 days.

For example:

• Cephalexin dosage for UTI: 500 mg every 12 hours for 7 days.
  
  
• Cephalexin dosage for tooth infection: 500 mg every 8 hours for 5–7 days.
  
  
• Cephalexin dosage for skin infection: 500 mg every 6 to 12 hours for 7–10 days.
  
  
• Cephalexin dosage for sinus infection: Often 500 mg every 8 or 12 hours for 10–14 days.
  
  

Always follow your healthcare provider’s instructions, as misuse can lead to antibiotic resistance or treatment failure.

How Long Does It Take for Cephalexin to Work?

Most people begin to notice improvement in symptoms within 24 to 48 hours after starting cephalexin 500 mg. However, it’s crucial to complete the full course of antibiotics — even if you feel better — to ensure the infection is fully eradicated and doesn’t return stronger.

Can You Take Cephalexin with Food, Dairy, or Alcohol?

Cephalexin can be taken with or without food, though taking it with food may help reduce stomach upset. While dairy does not significantly interfere with cephalexin, it’s a good idea to separate antibiotic and calcium-rich meals by a couple of hours to optimize absorption.

As for alcohol, moderate consumption doesn’t usually interact directly with cephalexin. However, alcohol can impair immune function, delay recovery, and increase the risk of side effects like nausea or dizziness. It’s best to avoid alcohol until the infection is fully treated.

Cephalexin Side Effects

While cephalexin is generally well-tolerated, some people may experience side effects. These can range from mild to serious.

Common side effects of cephalexin 500 mg include:

• Nausea
  
  
• Diarrhea
  
  
• Abdominal pain
  
  
• Headache
  
  
• Dizziness
  
  

More serious side effects may include:

• Severe allergic reactions (rash, itching, swelling, trouble breathing)
  
  
• Cephalexin yeast infection (especially in women)
  
  
• Clostridium difficile-associated diarrhea (a rare but serious form of antibiotic-related colitis)
  
  

If you experience symptoms of an allergic reaction or severe diarrhea, seek medical attention immediately.

Cephalexin Interactions with Other Medications

Before starting cephalexin, tell your healthcare provider about all medications and supplements you’re taking. Notable cephalexin interactions include:

• Metformin – may increase the risk of low blood sugar
  
  
• Probenecid – can raise cephalexin blood levels
  
  
• Live vaccines – such as typhoid, which may be less effective
  
  

Cephalexin may also interact with anticoagulants, so patients taking blood thinners like warfarin should be closely monitored.

Missed Dose or Overdose: What to Do?

If you miss a dose of cephalexin, take it as soon as you remember. If it’s almost time for your next dose, skip the missed dose — don’t double up.

In case of cephalexin overdose, symptoms may include:

• Severe nausea or vomiting
  
  
• Stomach pain
  
  
• Diarrhea
  
  
• Blood in the urine
  
  
• Seizures (rare)
  
  

Contact poison control or seek emergency medical attention if an overdose is suspected.

Cephalexin and Yeast Infections

A known risk of antibiotics like cephalexin is disruption of the natural microbiome, which can lead to yeast infections. Women taking cephalexin 500 mg are more susceptible to vaginal yeast infections, especially if they are prone to them or on longer treatment durations.

Signs of a yeast infection include:

• Vaginal itching or irritation
  
  
• Thick, white discharge
  
  
• Burning during urination
  
  

If this occurs, consult your doctor. You may be prescribed antifungal medication.

Can Cephalexin Treat STDs or Viral Infections?

Cephalexin does not treat STDs like chlamydia or gonorrhea, nor is it effective against viral infections like the common cold or flu. Misusing cephalexin for viral infections won’t help and may promote antibiotic resistance.

Storage, Expiration, and Shelf Life

Store cephalexin capsules at room temperature, away from moisture and heat. If you’re prescribed cephalexin suspension, it should be refrigerated and discarded after 14 days.

Wondering how long you can use cephalexin after the expiration date? It’s best not to use expired antibiotics. While they may not be harmful, their potency may be reduced, making them less effective — and potentially dangerous if the infection isn’t fully treated.

Final Thoughts: When to Call Your Doctor

Cephalexin 500 mg is an effective, trusted antibiotic for treating a variety of bacterial infections. While it’s generally safe, you should always follow your doctor’s guidance and report any unexpected side effects. Whether you’re treating a UTI, sinus infection, or skin issue, cephalexin can offer fast, reliable relief when used correctly.

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If you’re using antibiotics like Cephalexin 500 mg, it’s important to understand not just the medication, but the bigger picture of your overall health. At Asana Recovery, we know that physical infections and mental health challenges often go hand in hand—especially when substance use or past trauma complicates recovery. Whether you’re managing a current condition or working toward long-term wellness, our team offers compassionate, evidence-based care to support every step of your healing journey. Contact Asana Recovery today to learn how we can help you achieve balance, recovery, and lasting health.

Frequently Asked Questions (FAQs)

1. What is cephalexin 500 mg used for?

Cephalexin 500 mg is prescribed to treat a wide range of bacterial infections, including urinary tract infections (UTIs), sinus infections, skin infections, ear infections, and respiratory infections like bronchitis or pneumonia. Doctors may also prescribe it for dental abscesses or tooth infections when the bacteria involved respond to cephalosporins.

2. How long does it take for cephalexin 500 mg to work?

Most people notice improvement within 24 to 48 hours of starting cephalexin 500 mg. However, you must complete the full cephalexin dosage regimen as prescribed — typically lasting 7 to 14 days — to ensure the infection is fully cleared and doesn’t return.

3. What is the usual dosage of cephalexin 500 mg for a UTI?

The typical cephalexin dosage for UTI is 500 mg every 12 hours for 7 days, but this can vary based on the severity of the infection and your doctor’s recommendation. Always follow medical guidance to avoid complications or antibiotic resistance.

4. Can I take cephalexin with food or dairy products?

Yes, cephalexin can be taken with or without food. Taking it with meals may reduce stomach upset. While dairy products don’t significantly interfere with cephalexin absorption, it’s generally advised to space out high-calcium foods or supplements to maximize effectiveness.

5. Is it safe to drink alcohol while taking cephalexin?

There’s no direct interaction between cephalexin and alcohol, but drinking can worsen side effects like dizziness or upset stomach and may impair your immune response. It’s best to avoid alcohol while taking cephalexin 500 mg to help your body recover fully.

6. What are the side effects of cephalexin 500 mg?

Common cephalexin side effects include:

• Nausea
  
  
• Diarrhea
  
  
• Abdominal pain
  
  
• Headache
  More serious reactions include:
  
  
• Allergic rash or swelling
  
  
• Severe diarrhea (C. difficile infection)
  
  
• Vaginal yeast infection from cephalexin
  
  

If any severe or unusual symptoms occur, seek medical attention immediately.

7. Can cephalexin cause a yeast infection?

Yes, like many antibiotics, cephalexin can cause yeast infections, especially in women. This happens because antibiotics disrupt the natural balance of bacteria, allowing yeast to overgrow. If you notice symptoms like itching or discharge, speak to your doctor.

8. What should I do if I miss a dose of cephalexin?

If you miss a dose of cephalexin 500 mg, take it as soon as you remember. If it’s almost time for the next dose, skip the missed one — don’t double up. Staying consistent helps maintain the correct antibiotic level in your system for effective treatment.

9. Are there any drug interactions with cephalexin?

Yes. Cephalexin interactions can occur with:

• Probenecid – increases cephalexin levels
  
  
• Metformin – may raise the risk of low blood sugar
  
  
• Blood thinners like warfarin – risk of bleeding
  
  
• Live vaccines – effectiveness may be reduced
  Always inform your doctor of all medications and supplements you take.
  
  

10. Can cephalexin treat a sinus infection?

Yes, cephalexin for sinus infection is a common prescription when the infection is bacterial and not caused by a virus. The usual cephalexin dosage for sinus infection is 500 mg every 8 or 12 hours for 10 to 14 days, depending on severity and your doctor’s advice.

11. How long does cephalexin stay in your system after the last dose?

Cephalexin has a short half-life of about 1 hour, so it typically leaves the body within 8 to 12 hours after your last dose. However, its effects can persist longer in people with kidney impairment, so dosage adjustments may be needed.

12. Can I take cephalexin if I’m allergic to penicillin?

Some people who are allergic to penicillin may also react to cephalosporins like cephalexin. If you’ve ever had a serious allergic reaction to penicillin, tell your doctor before taking cephalexin 500 mg.

13. Does cephalexin expire? Can I take it after the expiration date?

Yes, cephalexin expires, and it’s not recommended to use it past its expiration date. While expired cephalexin may not be dangerous, its effectiveness can be significantly reduced, putting you at risk of an unresolved infection or complications. Always check the label and dispose of expired medication properly.

Informational Sources

• Centers for Disease Control and Prevention. (2023). Antibiotic prescribing and use: Cephalosporins. U.S. Department of Health & Human Services. https://www.cdc.gov/antibiotic-use/community/for-hcp/outpatient-hcp/cephalosporins.html
  
  Drugs.com. (2024). Cephalexin. https://www.drugs.com/cephalexin.html
  
  Mayo Clinic. (2024). Cephalexin (Oral Route) – Description and Brand Names. https://www.mayoclinic.org/drugs-supplements/cephalexin-oral-route/description/drg-20073315
  
  MedlinePlus. (2024). Cephalexin. National Library of Medicine. https://medlineplus.gov/druginfo/meds/a682733.html
  
  National Center for Biotechnology Information. (2021). Cephalexin. In PubChem Compound Summary. National Institutes of Health. https://pubchem.ncbi.nlm.nih.gov/compound/Cephalexin
  
  WebMD. (2024). Cephalexin Oral: Uses, Side Effects, Interactions, Pictures, Warnings & Dosing. https://www.webmd.com/drugs/2/drug-8657/cephalexin-oral/details
  
  NHS. (2023). Cephalexin: Antibiotic used for bacterial infections. https://www.nhs.uk/medicines/cephalexin/