Amoxicillin is semisynthetic antibiotic in the penicillin family, a close relative of ampicillin. Amoxicillin is indicated for the treatment of the following infections8:
- 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)
Amoxicillin Efficacy 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. Studies comparing amoxicillin with penicillin V report comparable efficacy5.
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.
The maximum daily dosage for amoxicillin is 1.000 mg, although up to 1.500 mg is acceptable.
According to the recent data2, 4, once-daily amoxicillin dosing regimen is as effective as conventional twice daily regimen.
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.
- Amoxicillin is one of the safest antibiotics. Licensed for use in neonates
- Labeled as "Pregnancy category B". Safe for use by pregnant and lactating women who are not allergic to penicillins.
- 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 and can be taken with food.
- Amoxicillin penetrates into most body tissues and fluids, with the exception of brain and spinal fluid.
- 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.
- 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.
- 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
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. Andrews M, Condren M. Once-daily amoxicillin for pharyngitis. J Pediatr Pharmacol Ther. 2010 Oct;15(4):244-8.
- 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.
- 4. Llerena Santa Cruz ED, Buñuel Álvarez JC, Porcar Farrán D, Solà Pou J, Fortea Gimeno E, Cortés Marina RB, Mayol Canals L. Treatment of streptococcal tonsillitis with once-a-day amoxicillin: a meta-analysis. An Pediatr (Barc). 2011 Nov;75(5):298-306. PubMed
- 5. Lennon DR, Farrell E, Martin DR, Stewart JM. Once-daily amoxicillin versus twice-daily penicillin V in group A beta-haemolytic streptococcal pharyngitis. Arch Dis Child. 2008 Jun;93(6):474-8. PubMed
- 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. PubMed
- 7. Shulman ST, Bisno AL, Clegg HW, Gerber MA, Kaplan EL, Lee G, Martin JM, Van Beneden C. 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):1279-82. Available at Oxford University Press
- 8. Amoxicillin Prescribing Information PDF
By HealthyStock Research Group, October 2009
Medical resources reviewed: August 2018