Cephalexin for the treatment of strep throat

Cephalexin for strep throat
Medically reviewed by Dr. Mandy Liedeman


Antibiotics, such as Keflex (cephalexin), play a crucial role in treating bacterial infections affecting various areas like the lungs, ears, or skin. Despite the discontinuation of the name-brand Keflex in the U.S., its generic counterparts remain widely accessible. When dealing with infections, understanding the prescribed dosage is vital. While sore throats are typically manageable with home remedies, strep throat, marked by additional symptoms, may require medical attention. In this blog, we will explore the details of strep throat and assess the efficacy of cephalexin as a treatment option.

Is cephalexin good for strep throat?

Cephalexin, belonging to the cephalosporin antibiotic class alongside Keflex, Keftabs, and Biocef, has shown notable effectiveness in treating strep throat. In comparison to penicillin, cephalosporins like cephalexin and cefadroxil (Duricef) demonstrate approximately three times higher efficacy, making them a reliable choice in eradicating streptococcal infections. This conclusion is drawn from a comprehensive meta-analysis of 35 trials conducted by medical professionals, which highlights the efficacy of cephalexin as a viable treatment option for strep throat.

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How does cephalexin work for strep throat?

Cephalexin works by preventing the growth of bacterial cell walls and hindering replication. 

  • Comparative Effectiveness: Cephalosporin antibiotics, including cephalexin, Keflex, Keftabs, and Biocef, are approximately three times more effective in eradicating strep than penicillin. This conclusion is derived from a meta-analysis of 35 trials, highlighting the superior efficacy of cephalosporins.
  • Targeting Peptidoglycan Synthesis: Within bacterial cells, peptidoglycan provides mechanical stability to the cell wall. Cephalexin, along with other beta-lactam antibiotics, utilizes its beta-lactam ring to inhibit the synthesis of peptidoglycan, a critical step in forming the bacterial cell wall.

This multi-faceted approach showcases how cephalexin effectively combats strep throat, especially for individuals with penicillin allergies.

How long does cephalexin take to work for strep?

Individuals taking cephalexin for strep throat can expect to experience initial relief within two to three days. Often, complete recovery is achieved within five days of starting the antibiotic course. Despite feeling better, it’s essential not to halt antibiotic treatment prematurely.

According to the Centers for Disease Control and Prevention (CDC), most individuals will notice significant improvement 1–2 days after initiating antibiotics. The CDC recommends consulting a doctor if there’s no improvement within 48 hours of antibiotic use. It’s essential to adhere to the prescribed course of antibiotics as advised by healthcare professionals.

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Can cephalexin 500mg be used for strep throat?

Yes, cephalexin 500mg can be taken for strep throat. The usual adult dose of cephalexin is 250 mg taken every 6 hours. For certain infections like streptococcal pharyngitis, skin and skin structure infections, and uncomplicated cystitis in patients over 15 years, a dosage of 500 mg may be administered every 12 hours. Adult dosing options include 250 mg four times per day or 500 mg twice per day, both lasting 7 to 14 days.

How long is strep contagious after cephalexin?

People undergoing cephalexin (Keflex) treatment for strep throat experience a reduction in contagiousness within 24 to 48 hours. Strep throat can remain contagious for approximately 2-3 weeks in individuals not undergoing antibiotic treatment. 

Individuals who take antibiotics for strep throat typically cease to be contagious around 24 to 48 hours after initiating the antibiotic therapy. During the timeline of contagiousness, take precautions to prevent the spread. Adhering to the prescribed antibiotic course aids in minimizing the duration of contagiousness.

Is Keflex better than amoxicillin for strep?

Antibiotics, crucial for treating bacterial infections, include beta-lactam types like penicillin, which damages bacterial cell walls, impeding reproduction and aiding the body in clearing the infection.

Cephalexin, belonging to the cephalosporin class of beta-lactam antibiotics, offers an alternative mechanism to combat bacterial infections. Amoxicillin and cephalexin are commonly prescribed beta-lactam antibiotics, each targeting different types of bacteria.

In the case of strep throat, cephalexin is found to be more effective than amoxicillin. Despite cephalexin’s effectiveness, amoxicillin remains the recommended first-line treatment for strep throat. The distinctions between Keflex (cephalexin) and amoxicillin in treating strep throat help healthcare professionals make informed decisions based on individual patient needs and considerations.

Is Keflex good for staph or strep?

Cephalexin (Keflex) maintains its effectiveness as a valuable antibiotic for treating both streptococcal and staphylococcal infections. Over twelve years of practical application, cephalexin has consistently demonstrated high efficacy, with cure rates reaching 90% or higher for streptococcal and staphylococcal infections.

Keflex exhibits excellent activity against both gram-positive staphylococci (staph) and streptococci (strep) bacteria.  Cephalexin is effective against susceptible isolates of various bacteria, including Staphylococcus aureus, Streptococcus pneumoniae, S. pyrogens, Haemophilus influenzae, Klebsiella pneumoniae, Moraxella catarrhalis, and Proteus mirabilis.

Keflex is a broad-spectrum antibiotic effective against both staphylococcal and streptococcal infections highlighting its versatility as a reliable antibiotic for a range of bacterial skin infections.

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Consult a doctor

If either you or your child has strep throat, it is crucial to make an appointment with your healthcare provider. Seeking medical attention ensures a professional assessment, accurate diagnosis, and appropriate treatment recommendations. If you are already taking cephalexin or any other antibiotic for strep throat and experience symptoms like fever, diarrhea, abdominal pain, blistering of skin, weakness, and clay-colored stool, consult a doctor without delay: 

Other FAQs about cephalexin for strep throat

Why do I feel weird after taking cephalexin?

Feeling unusual after taking cephalexin may result from common side effects such as diarrhea, nausea, vomiting, stomach pain, fatigue, or vaginal yeast infections. While these effects are generally mild, serious side effects are rare but can include seizures, infectious diarrhea, and bleeding. If you encounter any severe or persistent symptoms, it’s crucial to consult with your healthcare provider.

What bacteria does not respond to cephalexin?

Cephalexin is ineffective against methicillin-resistant staphylococci and most isolates of enterococci. Additionally, it does not act against most isolates of Enterobacter spp. Morganella morganii, and Proteus vulgaris. Furthermore, cephalexin has no activity against Pseudomonas spp. or Acinetobacter calcoaceticus.

Is 3 days of cephalexin enough?

No, three days is not enough to complete the course of cephalexin antibiotics. The duration of cephalexin treatment varies based on the type of infection. For certain infections, a prescribed course may be extended for at least 10 days. It’s essential to communicate with your doctor if you do not experience improvement within 2 to 3 days or if your condition worsens at any point. Completing the full prescribed course is crucial to prevent the risk of the infection returning. Avoid discontinuing the medication prematurely without consulting your healthcare provider.

Your Doctors Online uses high-quality and trustworthy sources to ensure content accuracy and reliability. We rely on peer-reviewed studies, academic research institutions and medical associations to provide up-to-date and evidence-based information to the users.

  • https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=694e406b-0dbd-47ef-b176-64d78ca836fa&type=display
  • Disney FA, Dillon H, Blumer JL, Dudding BA, McLinn SE, Nelson DB, Selbst SM. Cephalexin and penicillin in the treatment of group A beta-hemolytic streptococcal throat infections. Am J Dis Child. 1992 Nov;146(11):1324-7. doi: 10.1001/archpedi.1992.02160230082024. PMID: 1415072.
  • Scherger JE. What is proper medication for patients with strep throat? Am Fam Physician. 2010 Jun 1;81(11):1318; author reply 1318. PMID: 20521748.

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