Amoxicillin in Brief
- Generic name: Amoxicillin
- Brand names: Amoxil, Trimox
- Therapeutic class: Antibiotic
- Pharmacologic class: Aminopenicillin, Beta-lactam
- Pregnancy Category: B
- FDA Approved: 1974
- Chemical Formula: C16H19N3O5S
- Originally discovered: 1972, Beecham Research Laboratories,
Amoxicillin is a semisynthetic (synthesized from naturally occurring
substance) aminopenicillin antibiotic structurally related to ampicillin.
It is a moderate-spectrum antibiotic active against a wide range of Gram-positive,
and a limited range of Gram-negative organisms.
Amoxicillin was discovered by scientists at Beecham Research Laboratories
in 1972. In the US it is marketed by GlaxoSmithKline (the inheritor
company) under the original trade name Amoxil.
The narrow spectrum of antimicrobial activity of the penicillins,
led to the search for derivatives of penicillin which could treat a wider
range of infections. The first important step forward was the development
of ampicillin. Ampicillin had a broader spectrum of activity than either
of the original penicillins 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. It differs structurally from ampicillin merely by
having an additional hydroxyl group on the benzene ring. The main difference between ampicillin and amoxicillin is that amoxicillin is slightly more lipid soluble. As a result, amoxicillin may kill bacteria slightly quicker.
Amoxicillin is indicated for the treatment of the following infections
due to susceptible strains of sensitive organisms:
- Ear, nose, and throat infections - otitis media (middle ear
infection), pharyngitis (sore throat), sinusitis (sinus infection),
tonsillitis, and tonsillopharyngitis.
- Genitourinary tract infections - infections of the genital
organs (vagina, uterus, fallopian tubes/ovaries) and the urinary tract
(kidneys, ureters, bladder and urethra)
- Skin and skin structure infections - cellulitis (infection
of the dermis and subcutaneous tissue), erysipelas (superficial form
of cellulitis), folliculitis (inflammation of the hair follicles,
if the infection of the follicle is deeper and involves more follicles,
it moves into the furuncle and carbuncle), furuncles, carbuncles,
abscesses, impetigo (large vesicles or honey-crusted sores), infected
ulcers and infected burns and other.
- Lower respiratory tract infections - tracheobronchitis, bronchitis,
- Sexually transmitted diseases - gonorrhea, acute uncomplicated
(ano-genital and urethral infections)
- Helicobacter pylori infection eradication to reduce the
risk of duodenal ulcer recurrence
Off-label & Investigational uses
Off-label and investigational uses of amoxicillin include:
- Chlamydial infections. Chlamydia trachomatis is an obligate
intracellular bacteria, considered to be the most commonly sexually
transmitted organism. Amoxicillin is a recommended treatment of Chlamydia
infection during pregnancy by Centers for Disease Control and Prevention2,
8. However, it is not acceptable
for eradication of Chlamydia in other categories of people.
- Postexposure prophylaxis for anthrax. Amoxicillin has not
been approved by the FDA to use when treating people who have been
exposed to anthrax. However, if test results show that the anthrax
bacteria can be killed by penicillins, amoxicillin is recommended5
to prevent the development of anthrax disease in people who have been
exposed to anthrax, when first-line antibiotics
may be contraindicated.
- Endocarditis (inflammation of the inner lining of the heart).
Bacterial endocarditis is a relatively uncommon, life-threatening
infection of the inner lining of the heart. The most common antibiotic
used to prevent bacterial endocarditis is Amoxicillin6.
- Typhoid Fever (enteric fever). Typhoid fever is potentially
fatal if untreated. Amoxicillin is very effective and reduces the
risk of the carrier state. It is usually given for 14 days.
- Lyme disease. Lyme disease is caused by the spirochetal bacterium
Borrelia burgdorferi, and is transmitted to people by tick bites.
A 20 to 30 days course of amoxicillin is generally effective in early
disease7. Amoxicillin can
speed the healing of the erythema migrans rash and usually prevent
following symptoms such as arthritis or neurological problems.
- Prevention of postoperative oral infections11, especially when mandibular third molars and multiple avulsions are involved.
Amoxicillin "pros" and "cons"
- Better absorbed from the gastrointestinal tract than other penicillins
(penicillin V, ampicillin). Amoxicillin provides higher and more sustained blood antibiotic levels.
- Amoxicillin is the first choice for middle ear infection
- Excellent tissue penetration. Diffuses readily into
most body tissues and fluids, with the exception of brain and spinal fluid.
- It appears to be safe for use in pregnancy4
and is widely used in the treatment of various infections in pregnant women.
- Safe for children.
- Inexpensive and available in generic formulation.
- Long-established track record in scientific studies and in practice.
Amoxicillin has been extensively researched for more than 40 years.
- Allergy to amoxicillin (Penicillin hypersensitivity reaction).
The penicillin allergy results from the formation of an allergen
when the beta-lactam ring reacts with a terminal amine on a lysine
residue in a polypeptide. Every time a person is exposed to this
allergen, their immune system will sometimes cause a hypersensitivity (anaphylactic) reaction.
- More likely to cause diarrhea than other antibiotics 1.
- Test interactions. May interfere with urinary glucose tests using
cupric sulfate (Benedict's solution, Clinitest).
- Ineffective against beta-lactamase-producing bacteria.
- Tooth enamel defects. According to the recent study in
the Archives of Pediatrics and Adolescent Medicine9
the use of the amoxicillin during infancy appears to be linked to
tooth enamel defects in permanent teeth. However, further research is needed.
- Risk of antibiotic-induced rash in children with Epstein-Barr virus acute infectious mononucleosis (about 30%)10.
Mode of action
Amoxicillin is bactericidal (kills the bacteria). It
works by inhibiting the synthesis of bacterial cell walls during multiplication.
Amoxicillin inhibits the third and final stage
of bacterial cell wall synthesis by preferentially binding to specific
penicillin-binding proteins (PBPs) that are located inside the bacterial
cell wall. This results in a formation of defective cell wall and a cell death.
Due to the presence of a free amino group within the structure of aminopenicillins, they are able to penetrate
gram-negative bacteria more readily than the natural penicillins are.
Time to clear out of the system
The half-life of amoxicillin is about 61.3 minutes but in the absence
of renal function it is 7 to 10 hours. The half-life may be longer in
neonates and the elderly. In general, it takes 5-6 hours for amoxicillin to leave the system.
- 1. De Sutter AI, De Meyere MJ, Christiaens TC, Van Driel ML, Peersman W, De Maeseneer JM. J
Fam Pract. 2002 Apr;51(4):317-23.
- 2. Silverman NS, Sullivan M, Hochman M, Womack M, Jungkind DL. Am J Obstet Gynecol. 1994 Mar;170(3):829-32.
- 3. Ramakrishnan K, Sparks RA, Berryhill WE. Diagnosis and treatment of otitis media.
- 4. Jepsen P, Skriver MV, Floyd A, Lipworth L, Schnheyder HC, Srensen HT. A population-based study of
maternal use of amoxicillin and pregnancy outcome in Denmark. Br J Clin Pharmacol.
2003 Feb;55(2):216-21. PubMed
- 5. CDC Anthrax Guidelines for Pregnant Women Who Have Been Exposed to Anthrax But Do Not Have Symptoms
- 6. Kathryn A. Taubert, Adnan S. Dajani. Preventing Bacterial Endocarditis: American Heart
Association Guidelines. Vol. 57/No. 3 (February 1, 1998) AAFP
- 7. Guidelines for the management of Lyme disease
- 8. Sexually transmitted diseases treatment guidelines
- 9. 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
- 10. Chovel-Sella A, Ben Tov A, Lahav E, Mor O, Rudich H, Paret G, Reif S. Incidence of rash after amoxicillin treatment in children with infectious mononucleosis. Pediatrics. 2013 May
- 11. Sixou M, Burban J, Lakhssassi N, Duran D, De Mello G, Quéro J. Amoxicillin prophylaxis in oral surgery. Rev Stomatol Chir Maxillofac. 2012 Nov
Published: March 31, 2008
Last updated: July 28, 2014
- Amoxicillin is one of the oldest, yet still most frequently prescribed antibiotic in the world.
- Penicillins are either biosynthetic agents (chemical compound
produced by a living organism) derived from the fermentation of
various species of the mold Penicillium, or semi-synthetic agents
in which the substance 6-aminopenicillanic acid (6-APA), found in
all penicillins, is chemically altered in various ways.