Amoxicillin

Uses

Amoxicillin is licensed in the EU for the treatment of susceptible infections. Local antimicrobial guidelines (e.g., HSE/HPRA in Ireland, NICE/BNF in the UK) may specify preferred first-line choices and dosing. Typical indications include:

• ENT infections: Acute otitis media, acute bacterial sinusitis, streptococcal pharyngitis/tonsillitis (including eradication of Streptococcus pyogenes). In regions with high macrolide resistance, amoxicillin remains a key first-line agent for susceptible streptococcal disease.
• Lower respiratory tract infections: Acute exacerbations of chronic bronchitis (AECOPD) when bacterial, and community-acquired pneumonia (CAP) where S. pneumoniae is suspected and local resistance permits. (For atypicals such as Mycoplasma/Chlamydophila a macrolide or tetracycline may be preferred; clinicians tailor therapy.)
• Urinary tract infections (UTI): Uncomplicated cystitis and susceptible pyelonephritis; many E. coli isolates now produce β-lactamases, so prescribers may choose alternatives (e.g., nitrofurantoin, pivmecillinam) or use co-amoxiclav guided by culture.
• Skin/soft tissue infections: Impetigo, erysipelas, cellulitis, and wound infections caused by susceptible organisms. If MRSA is a concern, other agents are required.
• Helicobacter pylori eradication (with PPI + clarithromycin or metronidazole): Part of triple therapy regimens for peptic ulcer disease, following local resistance data.
• Borrelia (Lyme disease) — early localized disease: An option where doxycycline is unsuitable (e.g., certain paediatric cases or pregnancy), following national guidance.

How to take

• Swallow capsules/tablets with water; the oral suspension should be measured with a dosing syringe/spoon for accuracy.
• Dosing and frequency depend on the infection type, severity, kidney function, and age/weight (in children doses are weight-based).
• Amoxicillin can be taken with or without food; food may reduce stomach upset.
• Finish the entire course as prescribed, even if symptoms improve early. Stopping too soon can allow infection to return and promotes resistance.
• If no improvement after 48–72 hours, or if symptoms worsen, contact your prescriber — culture results or a different antibiotic may be needed.

Amoxicillin is often very well tolerated and effective when used appropriately within antimicrobial stewardship principles.

Side Effects

Most side effects are mild and settle as treatment continues. Serious reactions are uncommon but need urgent medical attention.

Common

• Gastrointestinal: Nausea, soft stools/diarrhoea, abdominal discomfort. Taking with food and adequate fluids can help. Persistent watery diarrhoea or diarrhoea with cramps/fever may indicate C. difficile.
• Skin: Mild rash or itching; non-allergic rashes (especially with viral infections like EBV) can occur and are not the same as true penicillin allergy.
• Oral/vaginal thrush: Disturbance of normal flora can lead to candidiasis; seek advice if symptomatic.

Uncommon

• Headache, dizziness.
• Changes in taste.
• Transient elevation of liver enzymes (ALT/AST) without symptoms.

Rare but serious — seek urgent care

• Allergic reactions (hypersensitivity): Hives, widespread rash, swelling of lips/face/tongue, wheeze, tight chest, difficulty breathing, or collapse (anaphylaxis). Stop the medicine and get emergency help.
• Severe skin reactions: Blistering/peeling rash, mucosal involvement (SJS/TEN) — extremely rare but medical emergencies.
• Cholestatic jaundice or hepatitis: Yellowing of skin/eyes, dark urine, pale stools, severe fatigue, right-upper-quadrant pain.
• Haematologic effects: Very rare anaemia, leucopenia, thrombocytopenia, or positive Coombs test; usually reversible on stopping.

C. difficile–associated diarrhoea can occur during or after antibiotics. If you develop severe/persistent diarrhoea (especially with blood/mucus), contact your clinician promptly and avoid anti-diarrhoeals unless advised.

Warnings & Precautions

• Penicillin/β-lactam allergy: Do not take if you have a history of immediate hypersensitivity to penicillins or severe reactions to other β-lactams (e.g., cephalosporins, carbapenems). Discuss any remote childhood “penicillin allergy” with your clinician — many are not true allergies.
• Infectious mononucleosis (EBV): Amoxicillin often causes a prolonged maculopapular rash in EBV; avoid unless benefits outweigh risks and the diagnosis has been reviewed.
• Kidney impairment: Dose adjustments and extended intervals may be required; ensure good hydration.
• Liver considerations: Caution in significant hepatic dysfunction; monitor clinically if symptoms arise.
• Seizure risk: High doses in renal impairment may lower seizure threshold in susceptible patients; prescribers account for this.
• Pregnancy and breastfeeding: Amoxicillin is commonly used when needed in pregnancy; small amounts pass into breast milk and are generally considered compatible with breastfeeding. Monitor the infant for loose stools or thrush.
• Antibiotic stewardship: Use only for likely bacterial infections; avoid for viral illnesses. Follow local guidelines to minimise resistance.

If symptoms are not improving as expected, your prescriber may review cultures/susceptibilities or switch to co-amoxiclav or an alternative class depending on the pathogen and site.