[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/) › Amoxicillin [Pharmacology](https://durgical.com/en/pharmacology/) · [Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/) # Amoxicillin A well-absorbed oral penicillin for ear, sinus and chest infections; combined with other drugs it clears H. pylori from the stomach. Updated 2026-11-01 - Class: [Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/) - Enzyme: Penicillin-binding proteins (bacterial transpeptidases) - ATC code: J01CA04 - WHO Model List of Essential Medicines ✂**Penicillin-binding proteins (bacterial transpeptidases)**Amoxicillin ⓘ The figure shows the transpeptidase domain of PBP3 from Chlamydia trachomatis with amoxicillin bound; it stands for the PBPs of the bacteria amoxicillin treats. **Target in 3D:** Penicillin-binding proteins (bacterial transpeptidases). PDB structure 6I1F (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/6I1F) · Drag to rotate · pinch to zoom ## Mechanism of action Amoxicillin is an aminopenicillin: it acylates the PBPs and stops peptidoglycan cross-linking, like penicillin G. Its amino group widens the spectrum to some gram-negative bacteria, and it is stable in gastric acid, so it is well absorbed by mouth. β-lactamases destroy it, which is why it is often paired with clavulanic acid. - Absorbed from the gut and reaches the infected tissue - Binds and acylates the bacterial PBPs - Peptidoglycan cross-links stop forming - The wall fails and the bacterium lyses ## Pharmacokinetics **Absorption** Stable in gastric acid and rapidly absorbed by mouth, with or without food. **Elimination** Mostly unchanged in the urine; probenecid delays it. **Half-life** About 1 hour. ## Indications - Acute otitis media. [Acute otitis media →](https://durgical.com/en/conditions/acute-otitis-media/) - Acute bacterial sinusitis (alone or with clavulanic acid). [Acute rhinosinusitis →](https://durgical.com/en/conditions/acute-rhinosinusitis/) - Lower respiratory tract infections such as community-acquired pneumonia. [Community-acquired pneumonia →](https://durgical.com/en/conditions/community-acquired-pneumonia/) - H. pylori eradication, together with a proton pump inhibitor and clarithromycin. [Helicobacter pylori gastritis →](https://durgical.com/en/conditions/helicobacter-pylori-gastritis/) - Group A streptococcal pharyngitis. [Streptococcal pharyngitis →](https://durgical.com/en/conditions/streptococcal-pharyngitis/) ## Adverse effects ### Common - Nausea, vomiting and diarrhoea - Rash - An erythematous rash in a high share of patients with infectious mononucleosis (Epstein–Barr virus) who receive an aminopenicillin ### Serious (rare, important) - Anaphylaxis - Clostridioides difficile diarrhoea, from mild to fatal colitis - Cholestatic jaundice or hepatitis (rare) ## Contraindications - History of allergy to penicillins - Suspected infectious mononucleosis (rash is very likely) ## Key interactions **Probenecid** Reduces tubular secretion: higher and longer-lasting amoxicillin levels. **Tetracyclines, macrolides, chloramphenicol and sulfonamides** May reduce the bactericidal effect. **Combined oral contraceptives** Amoxicillin may make them less effective. ## What is monitored - Clinical response in the first days - Liver tests if jaundice appears with amoxicillin–clavulanic acid ## Memory aid Amoxicillin wears an amino 'passport' that gets it through gram-negative porin borders; show it to Epstein–Barr virus and you get a rash, not an allergy. ## Test yourself Think of the answer, then tap the question to see it. ## A teenager with sore throat and large lymph nodes gets a widespread rash after starting amoxicillin. What is the likely cause? Infectious mononucleosis (Epstein–Barr virus). The rash is a typical non-allergic reaction to aminopenicillins in EBV infection, and the antibiotic was not needed for a viral illness. ## Why can amoxicillin be given by mouth, unlike penicillin G? It is stable in gastric acid and rapidly absorbed from the gut, with or without food. ## Why is amoxicillin often combined with clavulanic acid? Clavulanic acid inhibits many β-lactamases, so it protects amoxicillin from bacteria that would otherwise destroy it. ## In H. pylori eradication, what are amoxicillin's usual partners? A proton pump inhibitor, which lowers gastric acid, plus another antibiotic such as clarithromycin. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/amoxicillin/) ## Related drugs - [Benzylpenicillin (penicillin G)](https://durgical.com/en/pharmacology/benzylpenicillin/) - [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/) - [Omeprazole](https://durgical.com/en/pharmacology/omeprazole/) ## Related conditions - [Acute otitis media](https://durgical.com/en/conditions/acute-otitis-media/) - [Acute rhinosinusitis](https://durgical.com/en/conditions/acute-rhinosinusitis/) - [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/) - [Helicobacter pylori gastritis](https://durgical.com/en/conditions/helicobacter-pylori-gastritis/) - [Streptococcal pharyngitis](https://durgical.com/en/conditions/streptococcal-pharyngitis/) [← Back to the class: Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [Amoxicillin: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a685001.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [DailyMed - amoxicillin- Amoxicillin capsule amoxicillin- Amoxicillin tablet, film coated](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=649d285c-8fcb-48dd-aa5e-2f34128102f5) (DailyMed (U.S. National Library of Medicine), 2026); [RCSB PDB - 6I1F: Crystal structure of TP domain from Chlamydia trachomatis Penicillin-Binding Protein 3 in complex with amoxicillin](https://www.rcsb.org/structure/6I1F) (RCSB Protein Data Bank, 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/amoxicillin/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/amoxicillin/