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Beta-lactam antibiotic (aminopenicillin) Pregnancy: Safe in pregnancy. Widely used.

Amoxicillin

Brand names: Amoxil

Adult dose

Dose: 250–500 mg three times daily (mild-moderate); 3 g BD (URTI)
Route: Oral or IV
Frequency: Three times daily (or twice daily for high-dose)
Max: 6 g/day (IV for severe infection)
Community pneumonia (mild): 500 mg TDS for 5 days. Strep throat: 500 mg BD for 10 days. H. pylori eradication: 1 g BD (with clarithromycin + PPI). UTI (women): 500 mg TDS for 3–7 days. Add to antifungal cover if immunocompromised.

Paediatric dose

Dose: 25 mg/kg
Route: Oral
Frequency: Three times daily
Max: 500 mg/dose (standard); 1 g/dose (severe)
Concentration: 125 mg/ml
1 month–1 year: 62.5 mg TDS. 1–5 years: 125 mg TDS. 5–18 years: 250 mg TDS (double for severe). IV: 20–30 mg/kg TDS. Neonates: 30 mg/kg BD–TDS.

Dose adjustments

Renal

Reduce dose or increase interval if eGFR <30; avoid if eGFR <10 unless haemodialysis.

Hepatic

No dose adjustment required.

Paediatric weight-based calculator

1 month–1 year: 62.5 mg TDS. 1–5 years: 125 mg TDS. 5–18 years: 250 mg TDS (double for severe). IV: 20–30 mg/kg TDS. Neonates: 30 mg/kg BD–TDS.

Clinical pearls

  • Rash in EBV (glandular fever) is a T-cell mediated phenomenon — not true penicillin allergy
  • Add clavulanate (co-amoxiclav) for beta-lactamase producing organisms
  • Dose-related diarrhoea is common — advise patient
  • Drug of choice for Group A strep pharyngitis, H. pylori, community CAP (with macrolide)

Contraindications

  • Penicillin hypersensitivity
  • Infectious mononucleosis (causes rash)

Side effects

  • Diarrhoea and GI upset
  • Rash (maculopapular — not penicillin allergy if EBV-associated)
  • Hypersensitivity reactions including anaphylaxis
  • Antibiotic-associated diarrhoea / C. difficile
  • Oral candidiasis

Interactions

  • Methotrexate — reduced excretion (increased toxicity)
  • Warfarin — may increase INR (monitor)
  • Oral contraceptives — small theoretical risk (additional contraception not routinely recommended)

Monitoring

  • Response to treatment
  • Rash development
  • Renal function (prolonged use)

Reference: BNFc; BNF; NICE NG120 UTIs; PHE UECAP guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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