Keflex: Uses, Dosage, Side Effects and Interactions

Keflex: Uses, Dosage, Side Effects and Interactions
Submitted and Medically Reviewed By: Dr. Mavra Farrukh


Cephalexin, commonly prescribed as Keflex, is an antibiotic used to treat bacterial infections in adults and children (at least 1-year-old).

Keflex helps treat skin, bone, genitals, ears and urinary tract infections. Additionally, this medicine can be prescribed for respiratory tract infections.

Cephalexin is classified as cephalosporin antibiotics. These work by eliminating bacteria. The FDA approved CephalexinCephalexin in 1971, and it is being sold under various brand names. 

What is Keflex?

Keflex’s generic name is Cephalexin which is a cephalosporin antibiotic. It works by eliminating bacteria in your body. Cephalexin treats infections caused by bacteria, including upper respiratory infections, skin infections, urinary tract infections, ear infections, and bone infections.

Common Brand names: Keflex, Biocef, Zartan, Panixine, Daxbia

Keflex uses, or some conditions that are treated with Keflex include:

  • Upper Respiratory Tract Infection
  • Bacterial Infection
  • Osteomyelitis
  • Otitis Media
  • Cystitis
  • Bacterial Endocarditis Prophylaxis
  • Pharyngitis
  • Prostatitis
  • Pyelonephritis
  • Soft Tissue Infection


Respiratory Tract Infections

Keflex is indicated for treating respiratory tract infections caused by bacteria such as Streptococcus pyogenes and Streptococcus pneumoniae. 

Otitis Media

Keflex is prescribed for treating otitis media caused by susceptible isolates of Staphylococcus aureus, Haemophilus influenzae, Streptococcus pneumoniae, Streptococcus pyogenes, and Moraxella catarrhalis.

Skin And Soft Tissue Infections

Keflex is indicated for treating skin infections caused by Gram-positive bacteria, including Staphylococcus aureus and Streptococcus pyogenes.

Bone Infections

Keflex is indicated for treating bone infections. These are usually caused by susceptible isolates of Staphylococcus aureus and Proteus mirabilis

Genitourinary Tract Infections

Keflex also treats genitourinary tract infections. Acute prostatitiscaused by susceptible isolates of Escherichia coliProteus mirabilis, and Klebsiella pneumoniae. In addition, Keflex for uti is commonly prescribed.

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How to use Keflex?

Take Cephalexin precisely as prescribed by your doctor. Make sure you read all the instructions on your prescription label before starting the medication and do not use Keflex to treat any other condition without consulting a doctor.

Consume Keflex antibiotics as prescribed and for the duration that it is prescribed. Skipping doses can increase your risk of developing antibiotic resistance. Also, do not share your medicine with another person, even if they have similar symptoms. 

This medicine may affect the results of specific medical tests. That is why it is essential to let your doctor know if you are currently on Keflex. The tablets/capsules should be stored at room temperature and should be protected from moisture, heat, and light. Measure liquid medicine carefully before consuming it. A syringe or a medicine dose-measuring device can also be used for accurate Keflex dosing. Store the liquid medication in the refrigerator and discard any unused liquid after 14 days.

Dosing information

Oral capsule (250 mg; 500 mg; 750 mg)

Oral powder for suspension (125 mg/5 mL; 250 mg/5 mL)

Cephalexin is used for various infections in adults and children at least 1-year-old. Keflex dosage depends on the condition that is being treated. For adults, Keflex 500 is commonly prescribed. 

Side effects of Keflex 

Common side effects may include:

  • diarrhea
  • nausea
  • Vomiting
  • stomach pain
  • indigestion
  • vaginal itching
  • vaginal discharge

Besides these, Keflex side effects also include:

Hypersensitivity Reactions

Allergic reactions can occur with the use of the Keflex pill. Allergic reaction to Keflex can range from a mild rash to urticaria, angioedema, or a severe form of anaphylaxis. Furthermore, erythema multiforme, Stevens-Johnson syndrome, or toxic epidermal necrolysis have also been reported. Therefore, before prescribing Keflex antibiotics, it is essential to inquire whether the patient has a history of hypersensitivity reactions to CephalexinCephalexin, cephalosporins, and penicillins. Keflex is discontinued if an allergic reaction occurs and appropriate treatment is started.

Clostridium Difficile-Associated Diarrhea

Clostridium difficile-associated diarrhea (CDAD) is acquired using antibiotics, including Keflex. Symptoms vary in severity and can present as mild diarrhea, which may convert to fatal colitis. In addition, treatment with antibiotics can affect the colon’s normal flora, leading to the overgrowth of C. difficile.

If CDAD is suspected or confirmed, the antibiotic is usually discontinued. Treatment options vary according to the clinical symptoms of the patient. Some treatment options include fluid and electrolyte management, antibiotic treatment of C. difficile, protein supplementation and surgical evaluation.

Direct Coombs’ Test Seroconversion

Positive direct Coombs’ tests can occur in patients during treatment with cephalosporins, including Keflex. Acute intravascular hemolysis can occur as a result of cephalexin therapy. If anemia develops while taking after CephalexinCephalexin, a diagnostic work-up for drug-induced hemolytic anemia is essential. Therefore, it is vital to discontinue CephalexinCephalexin and start appropriate treatment.

Seizure Potential

Some cephalosporins can trigger seizures, particularly in individuals with renal impairment when the Keflex dosing is not adjusted. If seizures occur, discontinue Keflex. Anticonvulsant therapy is started if needed.

Prolonged Prothrombin Time

Cephalosporins may also lead to prolonged prothrombin time. Those particularly at risk are patients with kidney or liver impairment, poor nutritional state, or those receiving prolonged antibacterial or anticoagulant therapy. In such cases, prothrombin time monitoring is indicated. 

Development Of Drug-Resistant Bacteria

Prescribing Keflex without a proven bacterial infection increases the risk of developing bacteria resistance.

Prolonged use of Keflex may lead to the overgrowth of nonsusceptible organisms..

Keflex Use In Specific Populations


Pregnancy Category B

There is insufficient data on studies in pregnant women. Therefore, this drug should be used during pregnancy only if absolutely needed. 

Nursing Mothers

Amounts of CephalexinCephalexin are excreted in human milk. Therefore, one should be cautious while prescribing Keflex to a nursing woman. 

Pediatric Use

The effectiveness and safety of Keflex in pediatric patients were established after clinical trials.

Geriatric Use

No noticeable differences between older and younger subjects were observed in effectiveness or safety between the two age groups. The kidney substantially excretes this drug, and the risk of toxic reactions is greater in patients with impaired renal function. Keflex side effects in adults because the elderly are more likely, especially if they have decreased renal function.

Renal Impairment

Keflex should be cautiously administered if renal function is impaired. Monitoring should be done if such is the case.


Do not take this antibiotic if you are allergic to Cephalexin or another cephalosporin including: 

  • cefaclor (Ceclor, Raniclor);
  • cefprozil (Cefzil);
  • cefuroxime (Ceftin);
  • cefdinir (Omnicef);
  • cefadroxil (Duricef);
  • cefazolin (Ancef, Kefzol);
  • cefditoren (Spectracef);
  • cefpodoxime (Vantin);
  • ceftibuten (Cedax)

 Inform your doctor if you have ever had

  • an allergy to drug (especially penicillin);
  • liver disease
  • kidney disease
  • intestinal problems like colitis.
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In case of an emergency or overdose

You should seek emergency medical help if you have signs of an allergic reaction (hives, swelling in your face or difficulty breathing) or a severe reaction (fever, sore throat, burning eyes, and a skin rash with blistering and peeling). 

Overdose symptoms include vomiting, nausea, diarrhea, stomach pain, and blood in your urine. Call the emergency helpline in case of an overdose. 

What should you do if you forget a dose?

Take medicine as soon as you remember, but skip the missed pill if it is almost time to take your next scheduled dose. Do not take multiple doses at the same time. 

What should you avoid when taking Keflex?

Drug Interactions

The following medicines may interact with Keflex:

  • metformin;
  • probenecid. 

Other drugs may interact with CephalexinCephalexin, including over-the-counter medicines, herbal products and vitamins.

When to Consult a Doctor

Report to your doctor at once if you have:

  • severe stomach ache
  • diarrhea that is watery or bloody 
  • fatigue
  • feeling light-headed
  • short of breath
  • easy bruising
  • seizure
  • pale skin, cold hands and feet
  • yellowed skin, dark-colored urine;
  • fever
  • weakness
  • pain in your side or lower back
  • painful urination

How to get Keflex prescription?

Keflex is prescribed to treat several bacterial infections. If you want to know Keflex dosage for skin infection or if you require Keflex for skin infection or need to discuss your symptoms, talk to our doctor at Your Doctors Online to get a prescription for Keflex.

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FAQs About Keflex Answered by Your Doctors Online

Is Keflex a very strong antibiotic?

Cephalexin commonly prescribed as Keflex is an antibiotic used to treat bacterial infections adults and children (at least 1-year-old). Keflex helps treat skin, bone, genitals, ears and urinary tract infections. Additionally, this medicine can be prescribed for respiratory tract infections.

How fast does Keflex start working?

Cephalexin is effective even as early as one hour after taking it. However, it can take up to 48 hours after taking the antibiotic to notice improvement. 

Is Keflex penicillin? 

Keflex generic name is Cephalexin. Cephalexin which is a cephalosporin antibiotic. It works by fighting and eliminating bacteria in your body. 

What happens if you double-dose Keflex? 

Doubling the dose can lead to overdose symptoms, including vomiting, diarrhea, stomach pain, and blood in your urine.

Does Keflex treat uti?

Keflex is used in adults to treat different types of bacterial infections, such as UTIs. 

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