Doxycycline vs. Keflex: What's the difference?

  • Doxycycline and Keflex (cephalexin) are antibiotics used to treat many different types of bacterial infections.
  • Brand names for doxycycline include Vibramycin, Oracea, Adoxa, Atridox, Acticlate, Acticlate Cap, Doryx, Doxteric, Doxy, and Monodox.
  • Keflex and Daxbia are brand names for cephalexin.
  • Doxycycline and Keflex are different types of antibiotics. Doxycycline is a tetracycline antibiotic and Keflex is a cephalosporin antibiotic.
  • Side effects of doxycycline and Keflex that are similar include diarrhea or loose stools, nausea, abdominal pain, or vomiting.
  • Side effects of doxycycline that are different from Keflex include tooth discoloration if used in persons below 8 years of age, and exaggerated sunburn.
  • Side effects of Keflex that are different from doxycycline include headaches, dizziness, skin rash, fever, abnormal liver tests, and vaginitis.

What are doxycycline and Keflex?

Doxycycline is a tetracycline class antibiotic used to treat a variety of infections, such as respiratory tract infections due to Hemophilus influenzae, Streptococcus pneumoniae, or Mycoplasma pneumoniae. Doxycycline also is used to treat nongonococcal urethritis (due to Ureaplasma), typhus, cholera, chancroid, brucellosis, Rocky Mountain spotted fever, anthrax, syphilis, acne, and periodontal disease.

Keflex (cephalexin) is a cephalosporin antibiotic, which is similar to penicillin in action and side effects. Bacteria susceptible to Keflex include Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, E. coli, and others. Keflex is used to treat infections such as middle ear infections (otitis media), tonsillitis, throat infections, laryngitis, bronchitis, pneumonia, urinary tract infections (UTIs), skin infections, and bone infections.

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Bowel regularity means a bowel movement every day. See Answer

What are the side effects of doxycycline and Keflex?

Doxycycline

Doxycycline is generally well tolerated. The most common side effects are:

  • Diarrhea or loose stools
  • Nausea
  • Abdominal pain
  • Vomiting

Tetracyclines, such as doxycycline, may cause tooth discoloration if used in persons below 8 years of age. Exaggerated sunburn can occur with tetracyclines; therefore, minimize sunlight exposure during treatment.

Keflex

The most common side effects of Keflex are:

  • Diarrhea
  • Nausea
  • Abdominal pain
  • Vomiting
  • Headaches
  • Dizziness
  • Skin rash
  • Fever
  • Abnormal liver tests
  • Vaginitis

Individuals who are allergic to penicillin may also be allergic to Keflex. Serious but rare reactions include seizures, severe allergic reactions (anaphylaxis), and low platelet or red blood cell count.

Keflex, like almost all antibiotics, may cause mild or severe cases of pseudomembranous colitis, a mild to severe inflammation of the colon. Antibiotics, including Keflex alter the types of bacteria in the colon and permit overgrowth of a bacterium called Clostridium difficile. Studies indicate that toxins produced by Clostridium difficile are a primary cause of pseudomembranous colitis.

What is the dosage of doxycycline vs. Keflex?

Doxycycline

  • The absorption of doxycycline is not markedly affected by food and, therefore, it can be taken with meals.
  • For most infections, doxycycline is taken once or twice daily for 7 to 14 days.
  • For adult infections, the usual dose of oral doxycycline is 200 mg on the first day of treatment (100 mg every 12 hours) followed by a dose of 100 to 200 mg/day as a single dose or divided and administered twice daily.

Keflex

  • The dose of Keflex for adults is 1 to 4 grams in divided doses.
  • The usual adult dose is 250 mg every 6 hours.
  • Some infections may be treated with 500 mg every 12 hours.
  • Children are treated with 25 to 100 mg/kg/day in divided doses.
  • The dosing interval may be every 6 or 12 hours depending on the type and seriousness of the infection.

SLIDESHOW

Bacterial Infections 101: Types, Symptoms, and Treatments See Slideshow

What drugs interact with doxycycline and Keflex?

Doxycycline

  • Do not take doxycycline at the same time as aluminum-, magnesium-, or calcium-based antacids such as Mylanta, Maalox, Tums, or Rolaids because, like food, these medications bind doxycycline in the intestine and prevent its absorption. Similarly, doxycycline should not be taken with minerals (such as calcium or iron) or with bismuth subsalicylate (Pepto Bismol).
  • Doxycycline may enhance the activity of warfarin (Jantoven, Coumadin) and cause excessive "thinning" of the blood leading to exaggerated bleeding, necessitating a reduction in the dose of warfarin.
  • Phenytoin (Dilantin), carbamazepine (Tegretol), and barbiturates (such as phenobarbital) may enhance the metabolism (destruction) of doxycycline, thus making it less effective.
  • Doxycycline may interfere with the action of penicillins and should not be combined with penicillins.
  • Doxycycline may also reduce the effectiveness of oral contraceptives.
  • Combining tetracycline and methoxyflurane (Penthrane) may reduce kidney function.

Keflex

  • Keflex may reduce the effect of BCG and typhoid vaccines. Keflex should not be combined with BCG or typhoid vaccine unless there are no other options.

Are doxycycline and Keflex safe to use while pregnant or breastfeeding?

Doxycycline

  • Tetracycline antibiotics, such as doxycycline, can have toxic effects on development of bone in the fetus. Therefore, tetracyclines are not recommended during pregnancy unless there is no other appropriate antibiotic.
  • Doxycycline is secreted into breast milk but the extent of absorption by the breastfed infant is not known. Since tetracyclines can cause toxic effects on bone, the use of tetracyclines in nursing mothers is of concern. The doctor must decide whether to recommend that a nursing mother discontinue nursing during treatment with tetracyclines or change to a different antibiotic.

Keflex

  • Keflex is excreted in breast milk. Keflex should be used with caution or stopped when breastfeeding.

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Summary

Doxycycline and Keflex (cephalexin) are antibiotics used to treat many different types of bacterial infections. Doxycycline is a tetracycline antibiotic and Keflex is a cephalosporin antibiotic, which is similar to penicillin in action and side effects.

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Medically Reviewed on 5/20/2019
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