Amoxicillin for Strep Throat

  • Generic name: Amoxicillin Trihydrate
  • Trade names: Amoxil, Trimox, Ospamox
  • Dosages:
    Tablets, chewable 200 mg, 400 mg;
    Tablets 500 mg, 875 mg;
    Capsules 250 mg, 500 mg;
    Powder for oral suspension 125 mg per 5 mL; 200 mg per 5 mL ; 250 mg per 5 mL; 400 mg per 5 mL
  • Pharmacologic category: Antibiotic, Aminopenicillins
  • Pregnancy risk factor: B

Medical uses

Amoxicillin is semisynthetic antibiotic in the penicillin family, a close relative of ampicillin. Amoxicillin is indicated for the treatment of the following infections:

  • Otitis media (ear infection)
  • Pharyngitis, tonsillitis, laryngitis
  • Skin and soft tissues infections due to Streptococci and susceptible Staphylococci
  • Pharyngitis, sinusitis, laryngitis and tonsillitis.
  • Tracheobronchitis, bronchitis, pneumonia.
  • Uncomplicated urinary tract infections
  • Helicobacter pylori infection - duodenal ulcer caused by H. pylori (in combination with clarithromycin and a PPI)

Pharmacological characteristics

  • Absorption: Rapidly absorbed after oral administration
  • Metabolism: Partially hepatic
  • Elimination half-life: Elimination is primarily via the kidneys and is rapid, with a relatively short half-life of approximately 1 hour.
  • Excretion: Approximately 60% excreted in the urine within 6 to 8 h as unchanged drug


  • Amoxicillin is one of the safest antibiotics. Licensed for use in neonates and children. Labeled as "Pregnancy category B".
  • Amoxicillin is better absorbed from the gastrointestinal tract than other penicillins (e.g. ampicillin). It provides higher and more prolonged levels of antibiotic in the blood.
  • Amoxicillin penetrates into most body tissues and fluids, with the exception of brain and spinal fluid.
  • Amoxicillin is approved for a broad range of infections and is prescribed as a first-line therapy for otitis media (middle ear infection), pharyngitis (sore throat), and sinusitis (sinus infection).
  • Group A streptococcus, the main bacterium causing strep throat, have been uniformly susceptible to amoxicillin and have not developed resistance, despite the long-term use of amoxicillin for Streptococcal Pharyngitis.
  • Inexpensive in comparison with many other antibiotics.
  • Safe for use by pregnant and lactating women who are not allergic to penicillins.


  • Ineffective against beta-lactamase-producing organisms.
  • There have been rare cases of severe allergic reactions including angioneurotic oedema, anaphylaxis, serum sickness, hypersensitivity vasculitis and interstitial nephritis.
  • Frequent gastrointestinal side effects, such as nausea, vomiting, and diarrhea. This is primarily due to the destruction of normal gut flora.
  • A recent study in the Archives of Pediatrics and Adolescent Medicine6 found the link between amoxicillin use during infancy and developmental enamel defects of permanent teeth. However, further research is needed.
  • Laboratory test interactions. High urine concentrations of amoxicillin may result in false-positive reactions when testing for the presence of glucose in urine using CLINITEST®, Benedict’s Solution, or Fehling’s Solution.

Amoxicillin for Strep Throat

Strep throat (bacterial pharyngitis) is caused by Streptococcus pyogenes, or group A beta-hemolytic streptococci (GABHS). GABHS accounts for about 15-30% of pharyngitis cases in children and 5-10% of cases in adults. Streptococcal pharyngitis occurs mainly in children 5 to 15 years of age, with the peak incidence during the first few years of school.

Strep throat is contagious and is spread by via the airborne route. The presence of strep bacteria can be confirmed with a throat culture.

Although strep throats are usually mild, and would often get better on their own, some untreated strep throats result in serious complications such as rheumatic fever (joint and heart disease) and post-streptococcal glomerulonephritis (inflammation of the kidneys).

Amoxicillin is very effective in the treatment of strep throat. It is convenient, inexpensive, and has relatively narrow spectrum. Streptococcus pyogenes are highly susceptible to amoxicillin and have not developed resistance to it. The IDSA's newly revised guidelines7 for Group A streptococcal pharyngitis advise that when a strep infection is confirmed by testing, it should be treated with penicillin or amoxicillin. Amoxicillin is often used in preference to penicillin V in children because of poor palatability of penicillin suspensions.

According to the recent data1 the rate of eradication of group A beta-hemolytic streptococci from the tonsils with amoxicillin is greater than 80%. In the US prospective observational study3 the elimination of strep throat symptoms was achieved in 84% of amoxicillin-treated children.

Amoxicillin potential benefits in the treatment of streptococcal pharyngitis:

  • Prevention of rheumatic fever
  • Prevention of suppurative complications
  • Shorten the course of the illness
  • Reduce transmission of the infection to others

Dosage for adults: 500 mg twice a day for 10 days.

Dosage for children: <40 kg, 375 mg twice a day for 10 days; >40 kg, 500 mg twice a day for 10 days.

If Amoxicillin is not working for Strep Throat...
In case of amoxicillin failure to cure streptococcal pharyngitis alternative treatments are used, e.g. azithromycin, cefuroxime, cefixime, cefdinir.
Reasons for amoxicillin treatment failure include recent repeated use of penicillin antibiotics, inadequate dosing, or resistant infection.

Contraindication: Amoxicillin should NOT be used when infectious mononucleosis is suspected.

Unlabeled uses

  • Chlamydia. Amoxicillin is a recommended treatment of Chlamydia during pregnancy by Centers for Disease Control and Prevention (CDC)5.
  • Prophylaxis (prevention) of inhalational anthrax. According to the CDC, amoxicillin may be used to prevent anthrax in people for whom other antibiotics are contraindicated (e.g. children and pregnant women)2.
  • Endocarditis. Amoxicillin is used for prevention of bacterial endocarditis, a potentially life-threatening infection of the inner surface of the heart or the heart valves. When alpha-hemolytic streptococci are likely causes of endocarditis, the recommended standard prophylactic regimen is a single dose of oral amoxicillin.
  • Lyme disease. Amoxicillin is the treatment of choice for most adults and children. Amoxicillin (3-4 weeks therapy) is generally effective in early disease4.

Mode of action

Amoxicillin has a moderate spectrum of antibacterial activity, which includes a wide range of Gram-positive and a limited range of Gram-negative organisms.

Amoxicillin is a bactericidal antibiotic (kill the bacteria). It prevents bacterial cell wall mucopeptide synthesis by acylating the enzyme transpeptidase, thus making it unable to cross-link muramic acid containing peptidoglycan strands. This inhibition of the biosynthesis of dipeptidoglycan, a substance necessary for cell wall strength and rigidity, results in a defective cell wall.

Reviews, Discussions, Forums


  • 1. Brook I, Gober AE. Rate of eradication of group A beta-hemolytic streptococci in children with pharyngo-tonsillitis by amoxicillin. Int J Pediatr Otorhinolaryngol. 2009 May;73(5):757-9 PubMed
  • 2. Guidelines for Pregnant Women Who Have Been Exposed to Anthrax But Do Not Have Symptoms. CDC
  • 3. Curtin-Wirt C, Casey JR, Murray PC, Cleary CT, Hoeger WJ, Marsocci SM, Murphy ML, Francis AB, Pichichero ME. Efficacy of amoxicillin in children with group A beta hemolytic streptococcal tonsillopharyngitis. Clin Pediatr (Phila). 2003 Apr;42(3):219-25. SagePub
  • 4. Monsel G, Canestri A, Caumes E. Antibiotherapy for early localized Lyme disease. Med Mal Infect. 2007 Jul-Aug;37(7-8):463-72
  • 5. Sexually transmitted diseases treatment guidelines 2002. CDC.
  • 6. Hong L, Levy SM, Warren JJ, Dawson DV, Bergus GR, Wefel JS. Association of amoxicillin use during early childhood with developmental tooth enamel defects. Arch Pediatr Adolesc Med. 2005 Oct;159(10):943-8.
  • 7. Shulman ST, Bisno AL, Clegg HW, Gerber MA, Kaplan EL, Lee G, Martin JM, Van Beneden C; Infectious Diseases Society of America. Clinical practice guideline for the diagnosis and management of group A streptococcal pharyngitis: 2012 update by the Infectious Diseases Society of America. Clin Infect Dis. 2012 Nov 15;55(10) Available at

Written by, October 2009.
Last updated: July, 2015

Interesting facts


  • Amoxicillin is usually very safe. The greatest risk is an allergic reaction, which can be severe.
  • Children are more likely to show allergy to amoxicillin on penicillin skin testing than adults, according to a study presented at the American College of Allergy, Asthma & Immunology 2010 Annual Scientific Meeting.
  • The narrow spectrum of activity of the penicillin led to the search for derivatives which could treat a wider range of infections. The first real step forward was in the form of ampicillin. Ampicillin offered a broader spectrum of activity than either of the original agents and allowed doctors to treat a broader range of both Gram-positive and Gram-negative infections. Further developments led to amoxicillin, with improved duration of action.

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