ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Antibiotic (Penicillin) Pregnancy: B — safe in pregnancy

Amoxicillin

Brand names: Amoxil

Adult dose

Dose: 250–500mg three times daily
Route: Oral or IV
Frequency: Three times daily
CAP (mild): 500mg TDS × 5 days. IV: 500mg–1g TDS. High-dose: 3g BD (H. pylori eradication). Otitis media: 500mg TDS × 5 days.

Paediatric dose

Dose: 25 mg/kg
Route: Oral
Frequency: Three times daily
Max: 500 mg per dose (1 g per dose for severe infection)
BNFc child 1 month–11 years: standard 250 mg three times daily (or 25 mg/kg TDS); severe infection or 12+ years 500 mg TDS (up to 1 g TDS for severe). CAP: BTS recommends 30 mg/kg TDS (= 90 mg/kg/day total).
Paediatric weight-based calculator

BNFc child 1 month–11 years: standard 250 mg three times daily (or 25 mg/kg TDS); severe infection or 12+ years 500 mg TDS (up to 1 g TDS for severe). CAP: BTS recommends 30 mg/kg TDS (= 90 mg/kg/day total).

Clinical pearls

  • NEVER give in suspected glandular fever (EBV/IM) — causes non-allergic florid maculopapular rash
  • First-line for CAP, otitis media, sinusitis, UTI in pregnancy
  • Penicillin allergy cross-reactivity with cephalosporins is ~2% (lower than historically thought)
  • Acid-stable — better oral bioavailability than ampicillin

Contraindications

  • Penicillin allergy
  • Infectious mononucleosis (IM — causes florid rash)

Side effects

  • Diarrhoea
  • Rash (especially in EBV — ampicillin rash ≠ true allergy)
  • Urticaria
  • Clostridium difficile (prolonged use)

Interactions

  • Methotrexate — reduced renal excretion
  • Warfarin — altered gut flora increases INR
  • Oral contraceptives — theoretical

Monitoring

  • Renal function (high doses or prolonged use)
  • Signs of rash

Reference: BNFc; NICE NG138 (Pneumonia); PHE Antibiotic Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways