Is Keflex (Cephalexin) a Broad-Spectrum Antibiotic?

Yes, Keflex is a broad-spectrum antibiotic. Keflex, the brand name for the antibiotic cephalexin, is an antibiotic prescribed to treat a number of bacterial infections, including urinary tract infections, respiratory infections, and some bone infections. 

A key feature of Keflex is that it is a broad-spectrum antibiotic, meaning it is effective against many types of bacteria. This makes it a more universal treatment that doctors can prescribe when they are unsure of the exact bacteria causing an infection. 

Key Takeaways:

  • Keflex is the brand name for cephalexin and it belongs to the cephalosporin class of antibiotics.
  • Cephalexin is a broad-spectrum antibiotic, making it effective against a wide range of bacterial infections.
  • Cephalexin is used to treat various types of infections, including urinary tract infections, respiratory infections, and bone infections.

Continue reading to learn more about Keflex and broad-spectrum antibiotics.

Table of Contents

What Exactly Are Broad-Spectrum Antibiotics?

Broad-spectrum antibiotics refer to medications that treat a wide range of bacterial infections. 

All bacteria possess a cell wall, which protects them and keeps their contents contained. However, there are differences in the cell walls, which fall within two categories: gram-positive and gram-negative. 

Gram-positive bacteria have a plasma membrane surrounded by a thick layer of peptidoglycan. In comparison, the peptidoglycan layer in gram-negative bacteria is thinner but surrounded by an outer membrane. The peptidoglycan layer easily absorbs antibiotics, but the outer membrane of gram-negative bacteria resists antibiotics, which is why these bacteria are more difficult to treat. In comparison, without the outer membrane, the peptidoglycan layers in gram-positive bacteria readily absorb antibiotics and are easier to treat. 

Knowing about these two categories is important for understanding broad-spectrum antibiotics. Medications considered narrow-spectrum can only treat one or a few types of bacteria that are all gram-positive or all gram-negative. In comparison, broad-spectrum antibiotics can treat a much greater amount of bacteria, and sometimes, this can even span across both categories. This last distinction makes broad-spectrum antibiotics advantageous treatments since they can treat both types of bacteria, no matter their cell wall differences, increasing the odds that the antibiotic can treat the bacteria even when the exact bacteria causing the infection is unknown. 

Is Cephalexin a Broad-Spectrum Antibiotic?

Cephalexin is a broad-spectrum antibiotic that exhibits activity against gram-positive and gram-negative bacteria. 

As a broad-spectrum antibiotic, cephalexin is a valuable treatment as doctors can start patients on it without waiting for the results of a cell culture since broad-spectrum antibiotics are more likely to be effective against multiple types of bacteria. Additionally, they can be helpful in cases where a doctor suspects that more than one type of bacteria is causing an infection simultaneously since one antibiotic can be used to treat both infections. 

More About Cephalexin

Cephalexin is an antibiotic prescribed to treat bacterial infections. It belongs to the cephalosporin class of antibiotics and also goes by the brand name of Keflex. Cephalexin treats bacterial infections by inhibiting the bacteria’s creation of peptidoglycan, a critical component of the bacteria’s cell wall. When the cell wall weakens, the membrane can burst, killing the cell.  


Cephalexin is prescribed to treat various bacterial infections, some of which include:

  • urinary tract infections
  • otitis media
  • respiratory infections
  • bone infections (due to Proteus mirabilis or Staphylococcus aureus
  • soft tissue infections (due to Streptococcus pyogenes or S aureus)

Side Effects

Some of the common side effects of cephalexin include:

  • nausea
  • diarrhea
  • vomiting
  • indigestion
  • vaginal discharge or itching
  • stomach pain

More severe side effects may also develop. Contact your doctor immediately if you experience:

  • unusual tiredness
  • shortness of breath
  • lightheadedness
  • severe stomach pain
  • watery or bloody diarrhea
  • pale skin or cold hands and feet
  • seizures
  • unusual bleeding
  • red or purple spots under the skin
  • easy bruising
  • weakness
  • dark colored urine
  • yellowed skin
  • painful urination
  • pain in the side or lower back

Some people may also be allergic to cephalexin, with side effects including difficulty breathing, hives, and swelling of the face or throat. Severe skin reactions may also occur, which can result in burning eyes, blistering and peeling skin, red or purple rash, skin pain, and a sore throat. If you experience any symptoms of an allergic or severe skin reaction, seek immediate medical attention. 

Examples of Broad-Spectrum Antibiotics

There are many other antibiotics considered broad-spectrum, some of which include:

  • ampicillin
  • doxycycline
  • minocycline
  • azithromycin
  • vancomycin
  • carbapenems
  • quinolones
  • tetracyclines (except sarecycline)
  • aminoglycosides (except streptomycin)
  • piperacillin and piperacillin/tazobactam
  • chloramphenicol
  • trimethoprim/sulfamethoxazole
  • ofloxacin

In Conclusion

Cephalexin, known by the brand name Keflex, is an antibiotic prescribed to treat bacterial infections. It accomplishes this by intervening in the bacteria’s cell wall production, leaving it with a weak wall that easily bursts. 

One key term used to describe cephalexin is broad-spectrum, which is applied to antibiotics that can treat infections due to a wider range of bacteria, as is the case with cephalexin. As a broad-spectrum antibiotic, cephalexin is a treatment that doctors can start right away since they do not have to wait for test results regarding the specific type of bacteria causing an infection. 


Content on the DrHouse website is written by our medical content team and reviewed by qualified MDs, PhDs, NPs, and PharmDs. We follow strict content creation guidelines to ensure accurate medical information. However, this content is for informational purposes only and not a substitute for professional medical advice, diagnosis, or treatment. For more information read our medical disclaimer.

Always consult with your physician or other qualified health providers about medical concerns. Never disregard professional medical advice or delay seeking it based on what you read on this website.

If you are experiencing high fever (>103F/39.4C), shortness of breath, difficulty breathing, chest pain, heart palpitations, abnormal bruising, abnormal bleeding, extreme fatigue, dizziness, new weakness or paralysis, difficulty with speech, confusion, extreme pain in any body part, or inability to remain hydrated or keep down fluids or feel you may have any other life-threatening condition, please go to the emergency department or call 911 immediately.



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