Amoxicillin (Amoxil®)

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, United Kingdom UK

Based on "Antibiotic and Chemotherapy"
written by Roger G. Finch


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 limited number of Gram-negative bacteria.


History of discovery

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 antimicrobial spectrum of 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.

FDA-approved Uses

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/tonsillitis (strep throat), sinusitis (sinus infection).
  • Genitourinary tract infections - infections of the genital organs (vagina, uterus, fallopian tubes/ovaries) and the urinary tract (kidneys, ureters, bladder and urethra). See Amoxicillin for UTIs
  • 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, lactational mastitis.
  • Lower respiratory tract infections - tracheobronchitis, bronchitis, pneumonia.
  • 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

  • Chlamydial infections. Chlamydia trachomatis is an obligate intracellular bacteria, considered to be the most commonly sexually transmitted organism. Currently Amoxicillin is a recommended only as an alternative choice for Chlamydia infection during pregnancy by Centers for Disease Control and Prevention2, 8. Amoxicillin is not acceptable for eradication of Chlamydia in other categories of people. See Amoxicillin for Chlamydia in pregnancy
  • 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.

Advantages of Amoxicillin

  • 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 (Otitis media)3.
  • 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.
  • No interactions with food or alcohol.

Disadvantages of Amoxicillin

  • 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.

FAQs about Amoxicillin

Time to clear out of the system

How long does amoxicillin stay in 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.

Does Amoxicillin make you sleepy or tired?

It is highly unlikely for amoxicillin to make you feel sleepy or fatigued. Amoxicillin does not produce side effects on central nervous system. Drowsiness, somnolence are also not typical for amoxicillin.

Is Amoxicillin a Sulfa drug?

Amoxicillin is NOT a sulfa drug. It does not contain sulfonamide molecular structure. So amoxicillin is safe for people with sulfa allergies.

Can Amoxicillin treat STDs?

What STDs can amoxicillin cure? Amoxicillin is approved for the treatment of the following STDs:

  • Acute uncomplicated gonorrhea. However, latest CDC Sexually Transmitted Diseases Treatment Guidelines12 do NOT recommed to treat gonorrhea with amoxicillin.
  • Chlamydia in pregnancy. Amoxicillin is now considered only as an alternative therapy for Chlamydia in pregnant women.

Amoxicillin and Alcohol compatibility

Can you drink alcohol during amoxicillin therapy? There are no drug interactions between alcohol and amoxicillin. Alcohol doesn't affect how amoxicillin works.

Further reading


  • 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. PubMed
  • 3. Ramakrishnan K, Sparks RA, Berryhill WE. Diagnosis and treatment of otitis media. AAFP 2007;76(11):1650-1658.
  • 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. Special Considerations for Prophylaxis for and Treatment of Anthrax in Pregnant and Postpartum Women CDC NCEZID
  • 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 ILADS
  • 8. CDC Sexually transmitted diseases treatment guidelines Chlamydial Infections.
  • 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
  • 12. CDC Sexually Transmitted Diseases Treatment Guidelines Gonococcal Infections

Published: March 31, 2008
Last updated: July 21, 2018

Interesting facts

Amoxicillin molecule
  • 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.

More Facts
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