Amoxicillin
An oral aminopenicillin for ear, throat, chest and urinary infections, also used with other drugs to clear H. pylori.
Drug card
- Class
- Penicillin
- How it works
- Blocking the enzymes that cross-link the bacterial cell wall, so bacteria burst
- Used for
- Middle ear infections (otitis media)
- Chest infections, including pneumonia
- Strep throat
- Sinusitis
- Known for
- Rash, very common in glandular fever
- Allergic reactions (hypersensitivity)
- Its name
- -cillin means a penicillin
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does amoxicillin work?
Amoxicillin is an aminopenicillin with a broader spectrum than benzylpenicillin, also reaching some Gram-negative bacteria such as Haemophilus influenzae, E. coli and Proteus mirabilis. It is stable in stomach acid and well absorbed by mouth. Beta-lactamases destroy it, so it is often combined with clavulanic acid.
Like other penicillins: Penicillins carry a beta-lactam ring that binds and inactivates penicillin-binding proteins (PBPs), the enzymes that cross-link peptidoglycan in the bacterial cell wall. The weakened wall gives way and dividing bacteria burst, so penicillins are bactericidal. Bacteria resist them by making beta-lactamases (penicillinases) or by changing their PBPs.
Uses
What is amoxicillin used for?
- Middle ear infections (otitis media)
- Chest infections, including pneumonia
- Strep throat
- Sinusitis
- Urinary tract infections
- H. pylori eradication, with other drugs
Side effects
Side effects of amoxicillin
- Rash, very common in glandular feverKnown for
- Allergic reactions (hypersensitivity)Known forSerious
- Diarrhea
- Nausea
- Vomiting
- C. difficile colitisSerious
- Severe skin reactions (SJS, TEN, DRESS)Serious
- Hepatitis and cholestatic jaundiceSerious
- Oral or vaginal thrush
- Tooth staining from the liquid (brushes off)
- Seizures (rare)Serious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Glandular fever (infectious mononucleosis): amoxicillin often causes a widespread red rash, so it is avoided.
- Warfarin: amoxicillin can raise the INR, so clotting is checked more often.
- Allopurinol makes amoxicillin rashes more likely; probenecid raises amoxicillin levels.
- Severe kidney impairment (GFR below 30 mL/min): the dose is reduced, as the kidneys clear it.
Good to know: Combined with clavulanic acid (co-amoxiclav) to overcome beta-lactamases, and with clarithromycin and a proton pump inhibitor to clear H. pylori.
Remember it
A way to remember it
Penicillins jam the wall builders: only growing bacteria, busy laying new wall, are killed.
The penicillin-binding proteins are the enzymes that link peptidoglycan strands into a firm wall. Penicillins block them, so bacteria die while they multiply; a drug that halts growth, such as a tetracycline, can blunt this effect.
Written for biofideX
Its name
-cillin means penicillin
Marks penicillins (6-aminopenicillanic acid derivatives), including benzylpenicillin. Beta-lactamase inhibitors given with them keep their own names: clavulanic acid, tazobactam.
- Every drug name stem
Its class
Penicillins
Other penicillins with a card:
Easily mixed up with cephalosporins, carbapenems and glycopeptides.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Amoxicillin capsules, tablets and oral suspension: label (DailyMed)
- Amoxicillin (NCI Thesaurus)
- About amoxicillin (NHS)
- Side effects of amoxicillin (NHS)
- Who can and cannot take amoxicillin (NHS)
- Amoxicillin and clavulanate potassium tablets: label (DailyMed)
- Clinical Guidance for Group A Streptococcal Pharyngitis (CDC)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Antibiotics: the cell wall
Amoxicillin is one of 12 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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