Amoxicillin
Brand names: Amoxil, Trimox, Ospamox
Aminopenicillin (beta-lactam antibiotic)
Amoxicillin is one of the most commonly prescribed antibiotics worldwide — a broad-spectrum penicillin used for respiratory, ear, urinary, and dental infections. It is safe in pregnancy and widely available as both tablets and syrup.
Drug Class
Aminopenicillin (beta-lactam antibiotic)
Category
Antibiotics
Forms Available
Capsules (250 mg, 500 mg), Tablets (875 mg, 1 g)
How It Works
Amoxicillin inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), blocking the cross-linking of peptidoglycan chains. The resulting unstable cell wall causes bacterial lysis and death. It works against a range of gram-positive and some gram-negative bacteria.
What It's Used For
- Community-acquired pneumonia
- Acute otitis media (ear infections in children)
- Streptococcal tonsillitis and pharyngitis
- Urinary tract infections (UTIs)
- Dental infections and dental prophylaxis
- H. pylori eradication (in combination with clarithromycin and a PPI)
- Lyme disease (early stage)
Available Forms
Side Effects
Common Side Effects
- Diarrhoea — common, especially at higher doses
- Nausea and stomach upset
- Skin rash — distinguish between a true allergic rash and the benign morbilliform rash that occurs with amoxicillin (especially with EBV mononucleosis)
- Oral or vaginal thrush (Candida) with prolonged use
Serious Side Effects
- Anaphylaxis (if penicillin allergic) — can be life-threatening
- Clostridium difficile infection (pseudomembranous colitis) — with prolonged use
- Stevens-Johnson syndrome (very rare)
Drug Interactions
- Warfarin — monitor INR; amoxicillin can disturb gut flora and affect INR
- Oral contraceptives — unlikely interaction clinically, but patient may choose to use additional contraception
- Methotrexate — reduced renal excretion, toxicity risk
- Allopurinol — increased risk of skin rash
When to Avoid
- Known allergy to penicillin antibiotics
- History of amoxicillin-associated jaundice or hepatic dysfunction
Patient Tips
- Complete the full course even if you feel better — stopping early risks resistance and relapse
- Take with food to reduce nausea and diarrhoea
- Oral suspension must be stored in the fridge and used within 14 days of preparation
- If you develop a rash, seek advice — some rashes with amoxicillin are not a true penicillin allergy
- Probiotics during antibiotic courses may help reduce diarrhoea
Amoxicillin-clavulanate (Co-amoxiclav)
Many bacteria produce beta-lactamase enzymes that break down penicillins like amoxicillin. Adding clavulanate — a beta-lactamase inhibitor — restores activity against these resistant strains.
Co-amoxiclav (Augmentin) is used for bites, sinusitis, more severe ear infections, and soft tissue infections where resistant organisms are suspected. It has higher rates of GI side effects than amoxicillin alone.
Antibiotic resistance: why it matters for your prescription
Amoxicillin resistance has increased significantly due to overuse. Your doctor's choice of whether to prescribe amoxicillin, add clavulanate, or choose a different antibiotic depends on likely local resistance patterns.
Do not pressure for antibiotics for viral infections (colds, flu, most sore throats) — they do not work against viruses and contribute to resistance.
Related Medicines
Medical disclaimer
This page is for educational reference only. Always follow the dosage and instructions given by your prescriber or pharmacist. Do not start, stop, or change medicines without medical advice.
Reviewed 2026-06-01 · Looms Medical Team