Amoxicillin vs. penicillin: What's the difference?

What is amoxicillin? What is penicillin?

Amoxicillin is a penicillin-type antibiotic, in the same drug class as ampicillin (Unasyn), piperacillin (Pipracil), and ticarcillin (Ticar). Penicillin-type antibiotics do not directly kill bacteria, but they stop bacteria from multiplying by preventing bacteria from forming the walls that surround them. The walls protect bacteria from their environment and keep the contents of the bacterial cell together. Amoxicillin is effective against different bacteria including H. influenzae, N. gonorrhoea, E. coli, Pneumococci, Streptococci, and some strains of Staphylococci. Amoxicillin is used to treat bacterial infections of the middle ear, tonsils, throat, larynx (laryngitis), respiratory tract, urinary tract, and skin. Amoxicillin also is used to treat gonorrhea.

Penicillin antibiotics are used to treat many types of bacterial infections of the middle ear, sinuses, stomach and intestines, bladder, and kidney. They also are used to treat pneumonia, blood infections (sepsis), uncomplicated gonorrhea, meningitis, endocarditis, and other serious infections. Many derivatives of penicillin have been developed that inhibit more types of bacteria than the original life-saving drug. Penicillin itself is active against streptococci (including Streptococcus pneumoniae), Listeria, Neisseria gonorrhoeae, Clostridium, Peptococcus, and Peptostreptococcus.

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What are the side effects of amoxicillin vs. penicillin?

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.

Penicillin

Side effects of penicillin antibiotics include

  • diarrhea,
  • dizziness,
  • heartburn,
  • insomnia,
  • nausea,
  • itching,
  • vomiting,
  • confusion,
  • abdominal pain,
  • easy bruising,
  • bleeding,
  • rash, and
  • allergic reactions.

Individuals 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

  • seizures,
  • kidney problems,
  • oral fungal infections,
  • severe allergic reactions (anaphylaxis), and
  • low blood platelet levels (thrombocytopenia) or red blood cell count.

Like other antibiotics, penicillin antibiotics can alter the normal bacteria in the colon and encourage overgrowth of some bacteria such as Clostridium difficile, which causes inflammation of the colon (C. difficile colitis or pseudomembranous colitis).

Signs and symptoms of C. difficile colitis include

  • diarrhea,
  • fever,
  • abdominal pain, and
  • possibly shock.

What is the dosage of amoxicillin vs. penicillin?

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.

Penicillin

Penicillin antibiotics are available as

  • tablets,
  • capsules,
  • powder for oral suspension, and
  • powder for injection.

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Bowel regularity means a bowel movement every day. See Answer

What drugs interact with amoxicillin and penicillin?

Amoxicillin

Amoxicillin is rarely associated with important drug interactions.

Penicillin

Penicillin antibiotics have few important drug interactions.

  • Probenecid (Benemid) causes an increase in the amount of penicillins in the body by preventing excretion of penicillin by the kidneys.
  • Combining ampicillin with allopurinol (Zyloprim) can increase the incidence of drug-related skin rash.
  • Penicillin antibiotics may reduce the effect of BCG live vaccine and typhoid live vaccine.

Are amoxicillin and penicillin 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.

Penicillin

  • Penicillin antibiotics are considered safe to use during pregnancy.
  • Although small amounts of penicillins pass into breast milk they are considered safe to use while breastfeeding.

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Summary

Amoxicillin and penicillin are penicillin-type antibiotics used to treat various bacterial infections of the middle ear, sinuses, urinary tract, and respiratory tract. They are also used to treat gonorrhea. Penicillin-type antibiotics are also used to treat blood infections (sepsis), meningitis, endocarditis, and other serious infections.

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Medically Reviewed on 5/30/2019
References
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