Amoxicillin vs. doxycycline: What's the difference?

What is amoxicillin? What is doxycycline?

Amoxicillin is a penicillin-type antibiotic used to treat bacterial infections of the middle ear, tonsils, throat, larynx (laryngitis), bronchi (bronchitis), lungs (pneumonia), urinary tract, and skin. It also is used to treat gonorrhea. Other penicillin-type antibiotics include ampicillin (Unasyn), piperacillin (Pipracil), and ticarcillin (Ticar). These antibiotics stop bacteria from multiplying by preventing bacteria from forming the walls that surround them that are necessary to protect bacteria from their environment and to keep the contents of the bacterial cell together. Bacteria are unable survive without a cell wall. Amoxicillin is effective against many different bacterial strains including H. influenzae, E. coli, Pneumococci, N. gonorrhoea, Streptococci, and some strains of Staphylococci.

Doxycycline is a tetracycline antibiotic used for many different types of infections, including respiratory tract infections due to Hemophilus influenzae, Streptococcus pneumoniae, or Mycoplasma pneumoniae. It also is used to treat non-gonococcal urethritis (due to Ureaplasma), Rocky Mountain spotted fever, typhus, chancroid, cholera, brucellosis, anthrax, syphilis, acne, and periodontal disease. Doxycycline works by interrupting the production of proteins by bacteria.

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What are the side effects of amoxicillin and doxycycline?

Amoxicillin

Side effects due to amoxicillin include

People who are allergic to the cephalosporin class of antibiotics, which are related to the penicillins, for example, cefaclor (Ceclor), cephalexin (Keflex), and cefprozil (Cefzil), may or may not be allergic to penicillins.

Serious but rare reactions include:

Amoxicillin can alter the normal bacteria in the colon and encourage overgrowth of some bacteria such as Clostridium difficile which causes inflammation of the colon (pseudomembranous colitis). Patients who develop signs of pseudomembranous colitis after starting amoxicillin (diarrhea, fever, abdominal pain, and possibly shock) should contact their physician immediately.

Doxycycline

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

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

What is the dosage of amoxicillin vs. doxycycline?

Amoxicillin

  • For most infections in adults the dose of amoxicillin is 250 mg every 8 hours, 500 mg every 8 hours, 500 mg every 12 hours or 875 mg every 12 hours, depending on the type and severity of infection.
  • For the treatment of adults with gonorrhea, the dose is 3 g given as one dose.
  • For most infections, children older than 3 months but less than 40 kg are treated with 25 or 45 mg/kg/day in divided doses every 12 hours or 20 or 40 mg/kg/day with one-third of the daily dose given every 8 hours depending on the type and severity of the infection.
  • Amoxicillin can be taken with or without food.

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.

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What drugs interact with amoxicillin and doxycycline?

Amoxicillin

Amoxicillin is rarely associated with important drug interactions.

Doxycycline

  • It is recommended that doxycycline not be taken 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. It may also reduce the effect of oral contraceptives. Combining tetracycline and methoxyflurane (Penthrane) may reduce kidney function.

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

Amoxicillin

  • Penicillins are generally considered safe for use by pregnant women who are not allergic to penicillin.
  • Small amounts of amoxicillin may be excreted in breast milk and may cause diarrhea or allergic responses in nursing infants. Amoxicillin is generally considered safe to use while breastfeeding. Amoxicillin is used to treat infections in the newborn.

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 physician must decide whether to recommend that a nursing mother discontinue nursing during treatment with tetracyclines or change to a different antibiotic.

Summary

Amoxicillin (Moxatag, Amoxil) and doxycycline (Doryx, Vibramycin) are antibiotics used to treat bacterial infections of the respiratory tract and other infections. Amoxicillin is also used to treat bacterial infections of the middle ear, tonsils, throat, urinary tract, and skin. It also is used to treat gonorrhea. Doxycycline is also used to treat non-gonococcalurethritis (due to Ureaplasma), Rocky Mountain spotted fever, typhus, chancroid, cholera, brucellosis, anthrax, syphilis, acne, and periodontal disease. • Amoxicillin and doxycycline belong to different antibiotic drug classes. Amoxicillin is a penicillin-type antibiotic and doxycycline is a tetracycline antibiotic.

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Medically Reviewed on 5/29/2019
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